Node.js v21.0.0-nightly20231008fce8fbadcd documentation
- Node.js v21.0.0-nightly20231008fce8fbadcd
- ► Other versions
- ► Options
Table of contents
- About this documentation
- Usage and example
- Assert
- Strict assertion mode
- Legacy assertion mode
- Class: assert.AssertionError
- Class:
assert.CallTracker
assert(value[, message])
assert.deepEqual(actual, expected[, message])
assert.deepStrictEqual(actual, expected[, message])
assert.doesNotMatch(string, regexp[, message])
assert.doesNotReject(asyncFn[, error][, message])
assert.doesNotThrow(fn[, error][, message])
assert.equal(actual, expected[, message])
assert.fail([message])
assert.fail(actual, expected[, message[, operator[, stackStartFn]]])
assert.ifError(value)
assert.match(string, regexp[, message])
assert.notDeepEqual(actual, expected[, message])
assert.notDeepStrictEqual(actual, expected[, message])
assert.notEqual(actual, expected[, message])
assert.notStrictEqual(actual, expected[, message])
assert.ok(value[, message])
assert.rejects(asyncFn[, error][, message])
assert.strictEqual(actual, expected[, message])
assert.throws(fn[, error][, message])
- Asynchronous context tracking
- Introduction
- Class:
AsyncLocalStorage
new AsyncLocalStorage()
- Static method:
AsyncLocalStorage.bind(fn)
- Static method:
AsyncLocalStorage.snapshot()
asyncLocalStorage.disable()
asyncLocalStorage.getStore()
asyncLocalStorage.enterWith(store)
asyncLocalStorage.run(store, callback[, ...args])
asyncLocalStorage.exit(callback[, ...args])
- Usage with
async/await
- Troubleshooting: Context loss
- Class:
AsyncResource
new AsyncResource(type[, options])
- Static method:
AsyncResource.bind(fn[, type[, thisArg]])
asyncResource.bind(fn[, thisArg])
asyncResource.runInAsyncScope(fn[, thisArg, ...args])
asyncResource.emitDestroy()
asyncResource.asyncId()
asyncResource.triggerAsyncId()
- Using
AsyncResource
for aWorker
thread pool - Integrating
AsyncResource
withEventEmitter
- Async hooks
- Terminology
- Overview
async_hooks.createHook(callbacks)
- Class:
AsyncHook
- Promise execution tracking
- JavaScript embedder API
- Class:
AsyncLocalStorage
- Buffer
- Buffers and character encodings
- Buffers and TypedArrays
- Buffers and iteration
- Class:
Blob
- Class:
Buffer
- Static method:
Buffer.alloc(size[, fill[, encoding]])
- Static method:
Buffer.allocUnsafe(size)
- Static method:
Buffer.allocUnsafeSlow(size)
- Static method:
Buffer.byteLength(string[, encoding])
- Static method:
Buffer.compare(buf1, buf2)
- Static method:
Buffer.concat(list[, totalLength])
- Static method:
Buffer.copyBytesFrom(view[, offset[, length]])
- Static method:
Buffer.from(array)
- Static method:
Buffer.from(arrayBuffer[, byteOffset[, length]])
- Static method:
Buffer.from(buffer)
- Static method:
Buffer.from(object[, offsetOrEncoding[, length]])
- Static method:
Buffer.from(string[, encoding])
- Static method:
Buffer.isBuffer(obj)
- Static method:
Buffer.isEncoding(encoding)
- Class property:
Buffer.poolSize
buf[index]
buf.buffer
buf.byteOffset
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])
buf.entries()
buf.equals(otherBuffer)
buf.fill(value[, offset[, end]][, encoding])
buf.includes(value[, byteOffset][, encoding])
buf.indexOf(value[, byteOffset][, encoding])
buf.keys()
buf.lastIndexOf(value[, byteOffset][, encoding])
buf.length
buf.parent
buf.readBigInt64BE([offset])
buf.readBigInt64LE([offset])
buf.readBigUInt64BE([offset])
buf.readBigUInt64LE([offset])
buf.readDoubleBE([offset])
buf.readDoubleLE([offset])
buf.readFloatBE([offset])
buf.readFloatLE([offset])
buf.readInt8([offset])
buf.readInt16BE([offset])
buf.readInt16LE([offset])
buf.readInt32BE([offset])
buf.readInt32LE([offset])
buf.readIntBE(offset, byteLength)
buf.readIntLE(offset, byteLength)
buf.readUInt8([offset])
buf.readUInt16BE([offset])
buf.readUInt16LE([offset])
buf.readUInt32BE([offset])
buf.readUInt32LE([offset])
buf.readUIntBE(offset, byteLength)
buf.readUIntLE(offset, byteLength)
buf.subarray([start[, end]])
buf.slice([start[, end]])
buf.swap16()
buf.swap32()
buf.swap64()
buf.toJSON()
buf.toString([encoding[, start[, end]]])
buf.values()
buf.write(string[, offset[, length]][, encoding])
buf.writeBigInt64BE(value[, offset])
buf.writeBigInt64LE(value[, offset])
buf.writeBigUInt64BE(value[, offset])
buf.writeBigUInt64LE(value[, offset])
buf.writeDoubleBE(value[, offset])
buf.writeDoubleLE(value[, offset])
buf.writeFloatBE(value[, offset])
buf.writeFloatLE(value[, offset])
buf.writeInt8(value[, offset])
buf.writeInt16BE(value[, offset])
buf.writeInt16LE(value[, offset])
buf.writeInt32BE(value[, offset])
buf.writeInt32LE(value[, offset])
buf.writeIntBE(value, offset, byteLength)
buf.writeIntLE(value, offset, byteLength)
buf.writeUInt8(value[, offset])
buf.writeUInt16BE(value[, offset])
buf.writeUInt16LE(value[, offset])
buf.writeUInt32BE(value[, offset])
buf.writeUInt32LE(value[, offset])
buf.writeUIntBE(value, offset, byteLength)
buf.writeUIntLE(value, offset, byteLength)
new Buffer(array)
new Buffer(arrayBuffer[, byteOffset[, length]])
new Buffer(buffer)
new Buffer(size)
new Buffer(string[, encoding])
- Static method:
- Class:
File
node:buffer
module APIsBuffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
- C++ addons
- Node-API
- Implications of ABI stability
- Building
- Usage
- Node-API version matrix
- Environment life cycle APIs
- Basic Node-API data types
- Error handling
- Object lifetime management
- Module registration
- Working with JavaScript values
- Enum types
- Object creation functions
napi_create_array
napi_create_array_with_length
napi_create_arraybuffer
napi_create_buffer
napi_create_buffer_copy
napi_create_date
napi_create_external
napi_create_external_arraybuffer
napi_create_external_buffer
napi_create_object
napi_create_symbol
node_api_symbol_for
napi_create_typedarray
napi_create_dataview
- Functions to convert from C types to Node-API
napi_create_int32
napi_create_uint32
napi_create_int64
napi_create_double
napi_create_bigint_int64
napi_create_bigint_uint64
napi_create_bigint_words
napi_create_string_latin1
node_api_create_external_string_latin1
napi_create_string_utf16
node_api_create_external_string_utf16
napi_create_string_utf8
- Functions to convert from Node-API to C types
napi_get_array_length
napi_get_arraybuffer_info
napi_get_buffer_info
napi_get_prototype
napi_get_typedarray_info
napi_get_dataview_info
napi_get_date_value
napi_get_value_bool
napi_get_value_double
napi_get_value_bigint_int64
napi_get_value_bigint_uint64
napi_get_value_bigint_words
napi_get_value_external
napi_get_value_int32
napi_get_value_int64
napi_get_value_string_latin1
napi_get_value_string_utf8
napi_get_value_string_utf16
napi_get_value_uint32
- Functions to get global instances
- Working with JavaScript values and abstract operations
- Working with JavaScript properties
- Structures
- Functions
napi_get_property_names
napi_get_all_property_names
napi_set_property
napi_get_property
napi_has_property
napi_delete_property
napi_has_own_property
napi_set_named_property
napi_get_named_property
napi_has_named_property
napi_set_element
napi_get_element
napi_has_element
napi_delete_element
napi_define_properties
napi_object_freeze
napi_object_seal
- Working with JavaScript functions
- Object wrap
- Simple asynchronous operations
- Custom asynchronous operations
- Version management
- Memory management
- Promises
- Script execution
- libuv event loop
- Asynchronous thread-safe function calls
- Calling a thread-safe function
- Reference counting of thread-safe functions
- Deciding whether to keep the process running
napi_create_threadsafe_function
napi_get_threadsafe_function_context
napi_call_threadsafe_function
napi_acquire_threadsafe_function
napi_release_threadsafe_function
napi_ref_threadsafe_function
napi_unref_threadsafe_function
- Miscellaneous utilities
- C++ embedder API
- Child process
- Asynchronous process creation
- Synchronous process creation
- Class:
ChildProcess
- Event:
'close'
- Event:
'disconnect'
- Event:
'error'
- Event:
'exit'
- Event:
'message'
- Event:
'spawn'
subprocess.channel
subprocess.connected
subprocess.disconnect()
subprocess.exitCode
subprocess.kill([signal])
subprocess[Symbol.dispose]()
subprocess.killed
subprocess.pid
subprocess.ref()
subprocess.send(message[, sendHandle[, options]][, callback])
subprocess.signalCode
subprocess.spawnargs
subprocess.spawnfile
subprocess.stderr
subprocess.stdin
subprocess.stdio
subprocess.stdout
subprocess.unref()
- Event:
maxBuffer
and Unicode- Shell requirements
- Default Windows shell
- Advanced serialization
- Cluster
- How it works
- Class:
Worker
- Event:
'disconnect'
- Event:
'exit'
- Event:
'fork'
- Event:
'listening'
- Event:
'message'
- Event:
'online'
- Event:
'setup'
cluster.disconnect([callback])
cluster.fork([env])
cluster.isMaster
cluster.isPrimary
cluster.isWorker
cluster.schedulingPolicy
cluster.settings
cluster.setupMaster([settings])
cluster.setupPrimary([settings])
cluster.worker
cluster.workers
- Command-line API
- Synopsis
- Program entry point
- Options
-
--
--abort-on-uncaught-exception
--allow-child-process
--allow-fs-read
--allow-fs-write
--allow-worker
--build-snapshot
-c
,--check
--completion-bash
-C condition
,--conditions=condition
--cpu-prof
--cpu-prof-dir
--cpu-prof-interval
--cpu-prof-name
--diagnostic-dir=directory
--disable-proto=mode
--disallow-code-generation-from-strings
--dns-result-order=order
--enable-fips
--enable-network-family-autoselection
--enable-source-maps
--env-file=config
-e
,--eval "script"
--experimental-default-type=type
--experimental-import-meta-resolve
--experimental-loader=module
--experimental-network-imports
--experimental-permission
--experimental-policy
--experimental-sea-config
--experimental-shadow-realm
--experimental-test-coverage
--experimental-vm-modules
--experimental-wasi-unstable-preview1
--experimental-wasm-modules
--experimental-websocket
--force-context-aware
--force-fips
--force-node-api-uncaught-exceptions-policy
--frozen-intrinsics
--heap-prof
--heap-prof-dir
--heap-prof-interval
--heap-prof-name
--heapsnapshot-near-heap-limit=max_count
--heapsnapshot-signal=signal
-h
,--help
--icu-data-dir=file
--import=module
--input-type=type
--insecure-http-parser
--inspect[=[host:]port]
--inspect-brk[=[host:]port]
--inspect-port=[host:]port
--inspect-publish-uid=stderr,http
-i
,--interactive
--jitless
--max-http-header-size=size
--napi-modules
--no-addons
--no-deprecation
--no-experimental-fetch
--no-experimental-global-customevent
--no-experimental-global-webcrypto
--no-experimental-repl-await
--no-extra-info-on-fatal-exception
--no-force-async-hooks-checks
--no-global-search-paths
--no-network-family-autoselection
--no-warnings
--node-memory-debug
--openssl-config=file
--openssl-legacy-provider
--openssl-shared-config
--pending-deprecation
--policy-integrity=sri
--preserve-symlinks
--preserve-symlinks-main
-p
,--print "script"
--prof
--prof-process
--redirect-warnings=file
--report-compact
--report-dir=directory
,report-directory=directory
--report-filename=filename
--report-on-fatalerror
--report-on-signal
--report-signal=signal
--report-uncaught-exception
-r
,--require module
--secure-heap=n
--secure-heap-min=n
--snapshot-blob=path
--test
--test-name-pattern
--test-only
--test-reporter
--test-reporter-destination
--test-shard
--throw-deprecation
--title=title
--tls-cipher-list=list
--tls-keylog=file
--tls-max-v1.2
--tls-max-v1.3
--tls-min-v1.0
--tls-min-v1.1
--tls-min-v1.2
--tls-min-v1.3
--trace-atomics-wait
--trace-deprecation
--trace-event-categories
--trace-event-file-pattern
--trace-events-enabled
--trace-exit
--trace-sigint
--trace-sync-io
--trace-tls
--trace-uncaught
--trace-warnings
--track-heap-objects
--unhandled-rejections=mode
--use-bundled-ca
,--use-openssl-ca
--use-largepages=mode
--v8-options
--v8-pool-size=num
-v
,--version
--watch
--watch-path
--watch-preserve-output
--zero-fill-buffers
- Environment variables
FORCE_COLOR=[1, 2, 3]
NO_COLOR=<any>
NODE_DEBUG=module[,…]
NODE_DEBUG_NATIVE=module[,…]
NODE_DISABLE_COLORS=1
NODE_EXTRA_CA_CERTS=file
NODE_ICU_DATA=file
NODE_NO_WARNINGS=1
NODE_OPTIONS=options...
NODE_PATH=path[:…]
NODE_PENDING_DEPRECATION=1
NODE_PENDING_PIPE_INSTANCES=instances
NODE_PRESERVE_SYMLINKS=1
NODE_REDIRECT_WARNINGS=file
NODE_REPL_EXTERNAL_MODULE=file
NODE_REPL_HISTORY=file
NODE_SKIP_PLATFORM_CHECK=value
NODE_TEST_CONTEXT=value
NODE_TLS_REJECT_UNAUTHORIZED=value
NODE_V8_COVERAGE=dir
OPENSSL_CONF=file
SSL_CERT_DIR=dir
SSL_CERT_FILE=file
TZ
UV_THREADPOOL_SIZE=size
- Useful V8 options
- Console
- Class:
Console
new Console(stdout[, stderr][, ignoreErrors])
new Console(options)
console.assert(value[, ...message])
console.clear()
console.count([label])
console.countReset([label])
console.debug(data[, ...args])
console.dir(obj[, options])
console.dirxml(...data)
console.error([data][, ...args])
console.group([...label])
console.groupCollapsed()
console.groupEnd()
console.info([data][, ...args])
console.log([data][, ...args])
console.table(tabularData[, properties])
console.time([label])
console.timeEnd([label])
console.timeLog([label][, ...data])
console.trace([message][, ...args])
console.warn([data][, ...args])
- Inspector only methods
- Class:
- Corepack
- Crypto
- Determining if crypto support is unavailable
- Class:
Certificate
- Class:
Cipher
- Class:
Decipher
- Class:
DiffieHellman
diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])
diffieHellman.generateKeys([encoding])
diffieHellman.getGenerator([encoding])
diffieHellman.getPrime([encoding])
diffieHellman.getPrivateKey([encoding])
diffieHellman.getPublicKey([encoding])
diffieHellman.setPrivateKey(privateKey[, encoding])
diffieHellman.setPublicKey(publicKey[, encoding])
diffieHellman.verifyError
- Class:
DiffieHellmanGroup
- Class:
ECDH
- Static method:
ECDH.convertKey(key, curve[, inputEncoding[, outputEncoding[, format]]])
ecdh.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])
ecdh.generateKeys([encoding[, format]])
ecdh.getPrivateKey([encoding])
ecdh.getPublicKey([encoding][, format])
ecdh.setPrivateKey(privateKey[, encoding])
ecdh.setPublicKey(publicKey[, encoding])
- Static method:
- Class:
Hash
- Class:
Hmac
- Class:
KeyObject
- Class:
Sign
- Class:
Verify
- Class:
X509Certificate
new X509Certificate(buffer)
x509.ca
x509.checkEmail(email[, options])
x509.checkHost(name[, options])
x509.checkIP(ip)
x509.checkIssued(otherCert)
x509.checkPrivateKey(privateKey)
x509.fingerprint
x509.fingerprint256
x509.fingerprint512
x509.infoAccess
x509.issuer
x509.issuerCertificate
x509.keyUsage
x509.publicKey
x509.raw
x509.serialNumber
x509.subject
x509.subjectAltName
x509.toJSON()
x509.toLegacyObject()
x509.toString()
x509.validFrom
x509.validTo
x509.verify(publicKey)
node:crypto
module methods and propertiescrypto.constants
crypto.fips
crypto.checkPrime(candidate[, options], callback)
crypto.checkPrimeSync(candidate[, options])
crypto.createCipher(algorithm, password[, options])
crypto.createCipheriv(algorithm, key, iv[, options])
crypto.createDecipher(algorithm, password[, options])
crypto.createDecipheriv(algorithm, key, iv[, options])
crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])
crypto.createDiffieHellman(primeLength[, generator])
crypto.createDiffieHellmanGroup(name)
crypto.createECDH(curveName)
crypto.createHash(algorithm[, options])
crypto.createHmac(algorithm, key[, options])
crypto.createPrivateKey(key)
crypto.createPublicKey(key)
crypto.createSecretKey(key[, encoding])
crypto.createSign(algorithm[, options])
crypto.createVerify(algorithm[, options])
crypto.diffieHellman(options)
crypto.generateKey(type, options, callback)
crypto.generateKeyPair(type, options, callback)
crypto.generateKeyPairSync(type, options)
crypto.generateKeySync(type, options)
crypto.generatePrime(size[, options[, callback]])
crypto.generatePrimeSync(size[, options])
crypto.getCipherInfo(nameOrNid[, options])
crypto.getCiphers()
crypto.getCurves()
crypto.getDiffieHellman(groupName)
crypto.getFips()
crypto.getHashes()
crypto.getRandomValues(typedArray)
crypto.hkdf(digest, ikm, salt, info, keylen, callback)
crypto.hkdfSync(digest, ikm, salt, info, keylen)
crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)
crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)
crypto.privateDecrypt(privateKey, buffer)
crypto.privateEncrypt(privateKey, buffer)
crypto.publicDecrypt(key, buffer)
crypto.publicEncrypt(key, buffer)
crypto.randomBytes(size[, callback])
crypto.randomFillSync(buffer[, offset][, size])
crypto.randomFill(buffer[, offset][, size], callback)
crypto.randomInt([min, ]max[, callback])
crypto.randomUUID([options])
crypto.scrypt(password, salt, keylen[, options], callback)
crypto.scryptSync(password, salt, keylen[, options])
crypto.secureHeapUsed()
crypto.setEngine(engine[, flags])
crypto.setFips(bool)
crypto.sign(algorithm, data, key[, callback])
crypto.subtle
crypto.timingSafeEqual(a, b)
crypto.verify(algorithm, data, key, signature[, callback])
crypto.webcrypto
- Notes
- Crypto constants
- Debugger
- Deprecated APIs
- Revoking deprecations
- List of deprecated APIs
- DEP0001:
http.OutgoingMessage.prototype.flush
- DEP0002:
require('_linklist')
- DEP0003:
_writableState.buffer
- DEP0004:
CryptoStream.prototype.readyState
- DEP0005:
Buffer()
constructor - DEP0006:
child_process
options.customFds
- DEP0007: Replace
cluster
worker.suicide
withworker.exitedAfterDisconnect
- DEP0008:
require('node:constants')
- DEP0009:
crypto.pbkdf2
without digest - DEP0010:
crypto.createCredentials
- DEP0011:
crypto.Credentials
- DEP0012:
Domain.dispose
- DEP0013:
fs
asynchronous function without callback - DEP0014:
fs.read
legacy String interface - DEP0015:
fs.readSync
legacy String interface - DEP0016:
GLOBAL
/root
- DEP0017:
Intl.v8BreakIterator
- DEP0018: Unhandled promise rejections
- DEP0019:
require('.')
resolved outside directory - DEP0020:
Server.connections
- DEP0021:
Server.listenFD
- DEP0022:
os.tmpDir()
- DEP0023:
os.getNetworkInterfaces()
- DEP0024:
REPLServer.prototype.convertToContext()
- DEP0025:
require('node:sys')
- DEP0026:
util.print()
- DEP0027:
util.puts()
- DEP0028:
util.debug()
- DEP0029:
util.error()
- DEP0030:
SlowBuffer
- DEP0031:
ecdh.setPublicKey()
- DEP0032:
node:domain
module - DEP0033:
EventEmitter.listenerCount()
- DEP0034:
fs.exists(path, callback)
- DEP0035:
fs.lchmod(path, mode, callback)
- DEP0036:
fs.lchmodSync(path, mode)
- DEP0037:
fs.lchown(path, uid, gid, callback)
- DEP0038:
fs.lchownSync(path, uid, gid)
- DEP0039:
require.extensions
- DEP0040:
node:punycode
module - DEP0041:
NODE_REPL_HISTORY_FILE
environment variable - DEP0042:
tls.CryptoStream
- DEP0043:
tls.SecurePair
- DEP0044:
util.isArray()
- DEP0045:
util.isBoolean()
- DEP0046:
util.isBuffer()
- DEP0047:
util.isDate()
- DEP0048:
util.isError()
- DEP0049:
util.isFunction()
- DEP0050:
util.isNull()
- DEP0051:
util.isNullOrUndefined()
- DEP0052:
util.isNumber()
- DEP0053:
util.isObject()
- DEP0054:
util.isPrimitive()
- DEP0055:
util.isRegExp()
- DEP0056:
util.isString()
- DEP0057:
util.isSymbol()
- DEP0058:
util.isUndefined()
- DEP0059:
util.log()
- DEP0060:
util._extend()
- DEP0061:
fs.SyncWriteStream
- DEP0062:
node --debug
- DEP0063:
ServerResponse.prototype.writeHeader()
- DEP0064:
tls.createSecurePair()
- DEP0065:
repl.REPL_MODE_MAGIC
andNODE_REPL_MODE=magic
- DEP0066:
OutgoingMessage.prototype._headers, OutgoingMessage.prototype._headerNames
- DEP0067:
OutgoingMessage.prototype._renderHeaders
- DEP0068:
node debug
- DEP0069:
vm.runInDebugContext(string)
- DEP0070:
async_hooks.currentId()
- DEP0071:
async_hooks.triggerId()
- DEP0072:
async_hooks.AsyncResource.triggerId()
- DEP0073: Several internal properties of
net.Server
- DEP0074:
REPLServer.bufferedCommand
- DEP0075:
REPLServer.parseREPLKeyword()
- DEP0076:
tls.parseCertString()
- DEP0077:
Module._debug()
- DEP0078:
REPLServer.turnOffEditorMode()
- DEP0079: Custom inspection function on objects via
.inspect()
- DEP0080:
path._makeLong()
- DEP0081:
fs.truncate()
using a file descriptor - DEP0082:
REPLServer.prototype.memory()
- DEP0083: Disabling ECDH by setting
ecdhCurve
tofalse
- DEP0084: requiring bundled internal dependencies
- DEP0085: AsyncHooks sensitive API
- DEP0086: Remove
runInAsyncIdScope
- DEP0089:
require('node:assert')
- DEP0090: Invalid GCM authentication tag lengths
- DEP0091:
crypto.DEFAULT_ENCODING
- DEP0092: Top-level
this
bound tomodule.exports
- DEP0093:
crypto.fips
is deprecated and replaced - DEP0094: Using
assert.fail()
with more than one argument - DEP0095:
timers.enroll()
- DEP0096:
timers.unenroll()
- DEP0097:
MakeCallback
withdomain
property - DEP0098: AsyncHooks embedder
AsyncResource.emitBefore
andAsyncResource.emitAfter
APIs - DEP0099: Async context-unaware
node::MakeCallback
C++ APIs - DEP0100:
process.assert()
- DEP0101:
--with-lttng
- DEP0102: Using
noAssert
inBuffer#(read|write)
operations - DEP0103:
process.binding('util').is[...]
typechecks - DEP0104:
process.env
string coercion - DEP0105:
decipher.finaltol
- DEP0106:
crypto.createCipher
andcrypto.createDecipher
- DEP0107:
tls.convertNPNProtocols()
- DEP0108:
zlib.bytesRead
- DEP0109:
http
,https
, andtls
support for invalid URLs - DEP0110:
vm.Script
cached data - DEP0111:
process.binding()
- DEP0112:
dgram
private APIs - DEP0113:
Cipher.setAuthTag()
,Decipher.getAuthTag()
- DEP0114:
crypto._toBuf()
- DEP0115:
crypto.prng()
,crypto.pseudoRandomBytes()
,crypto.rng()
- DEP0116: Legacy URL API
- DEP0117: Native crypto handles
- DEP0118:
dns.lookup()
support for a falsy host name - DEP0119:
process.binding('uv').errname()
private API - DEP0120: Windows Performance Counter support
- DEP0121:
net._setSimultaneousAccepts()
- DEP0122:
tls
Server.prototype.setOptions()
- DEP0123: setting the TLS ServerName to an IP address
- DEP0124: using
REPLServer.rli
- DEP0125:
require('node:_stream_wrap')
- DEP0126:
timers.active()
- DEP0127:
timers._unrefActive()
- DEP0128: modules with an invalid
main
entry and anindex.js
file - DEP0129:
ChildProcess._channel
- DEP0130:
Module.createRequireFromPath()
- DEP0131: Legacy HTTP parser
- DEP0132:
worker.terminate()
with callback - DEP0133:
http
connection
- DEP0134:
process._tickCallback
- DEP0135:
WriteStream.open()
andReadStream.open()
are internal - DEP0136:
http
finished
- DEP0137: Closing fs.FileHandle on garbage collection
- DEP0138:
process.mainModule
- DEP0139:
process.umask()
with no arguments - DEP0140: Use
request.destroy()
instead ofrequest.abort()
- DEP0141:
repl.inputStream
andrepl.outputStream
- DEP0142:
repl._builtinLibs
- DEP0143:
Transform._transformState
- DEP0144:
module.parent
- DEP0145:
socket.bufferSize
- DEP0146:
new crypto.Certificate()
- DEP0147:
fs.rmdir(path, { recursive: true })
- DEP0148: Folder mappings in
"exports"
(trailing"/"
) - DEP0149:
http.IncomingMessage#connection
- DEP0150: Changing the value of
process.config
- DEP0151: Main index lookup and extension searching
- DEP0152: Extension PerformanceEntry properties
- DEP0153:
dns.lookup
anddnsPromises.lookup
options type coercion - DEP0154: RSA-PSS generate key pair options
- DEP0155: Trailing slashes in pattern specifier resolutions
- DEP0156:
.aborted
property and'abort'
,'aborted'
event inhttp
- DEP0157: Thenable support in streams
- DEP0158:
buffer.slice(start, end)
- DEP0159:
ERR_INVALID_CALLBACK
- DEP0160:
process.on('multipleResolves', handler)
- DEP0161:
process._getActiveRequests()
andprocess._getActiveHandles()
- DEP0162:
fs.write()
,fs.writeFileSync()
coercion to string - DEP0163:
channel.subscribe(onMessage)
,channel.unsubscribe(onMessage)
- DEP0164:
process.exit(code)
,process.exitCode
coercion to integer - DEP0165:
--trace-atomics-wait
- DEP0166: Double slashes in imports and exports targets
- DEP0167: Weak
DiffieHellmanGroup
instances (modp1
,modp2
,modp5
) - DEP0168: Unhandled exception in Node-API callbacks
- DEP0169: Insecure url.parse()
- DEP0170: Invalid port when using
url.parse()
- DEP0171: Setters for
http.IncomingMessage
headers and trailers - DEP0172: The
asyncResource
property ofAsyncResource
bound functions - DEP0173: the
assert.CallTracker
class - DEP0174: calling
promisify
on a function that returns aPromise
- DEP0175:
util.toUSVString
- DEP0176:
fs.F_OK
,fs.R_OK
,fs.W_OK
,fs.X_OK
- DEP0001:
- Diagnostics Channel
- DNS
- Class:
dns.Resolver
dns.getServers()
dns.lookup(hostname[, options], callback)
dns.lookupService(address, port, callback)
dns.resolve(hostname[, rrtype], callback)
dns.resolve4(hostname[, options], callback)
dns.resolve6(hostname[, options], callback)
dns.resolveAny(hostname, callback)
dns.resolveCname(hostname, callback)
dns.resolveCaa(hostname, callback)
dns.resolveMx(hostname, callback)
dns.resolveNaptr(hostname, callback)
dns.resolveNs(hostname, callback)
dns.resolvePtr(hostname, callback)
dns.resolveSoa(hostname, callback)
dns.resolveSrv(hostname, callback)
dns.resolveTxt(hostname, callback)
dns.reverse(ip, callback)
dns.setDefaultResultOrder(order)
dns.getDefaultResultOrder()
dns.setServers(servers)
- DNS promises API
- Class:
dnsPromises.Resolver
resolver.cancel()
dnsPromises.getServers()
dnsPromises.lookup(hostname[, options])
dnsPromises.lookupService(address, port)
dnsPromises.resolve(hostname[, rrtype])
dnsPromises.resolve4(hostname[, options])
dnsPromises.resolve6(hostname[, options])
dnsPromises.resolveAny(hostname)
dnsPromises.resolveCaa(hostname)
dnsPromises.resolveCname(hostname)
dnsPromises.resolveMx(hostname)
dnsPromises.resolveNaptr(hostname)
dnsPromises.resolveNs(hostname)
dnsPromises.resolvePtr(hostname)
dnsPromises.resolveSoa(hostname)
dnsPromises.resolveSrv(hostname)
dnsPromises.resolveTxt(hostname)
dnsPromises.reverse(ip)
dnsPromises.setDefaultResultOrder(order)
dnsPromises.getDefaultResultOrder()
dnsPromises.setServers(servers)
- Class:
- Error codes
- Implementation considerations
- Class:
- Domain
- Errors
- Error propagation and interception
- Class:
Error
- Class:
AssertionError
- Class:
RangeError
- Class:
ReferenceError
- Class:
SyntaxError
- Class:
SystemError
- Class:
TypeError
- Exceptions vs. errors
- OpenSSL errors
- Node.js error codes
ABORT_ERR
ERR_ACCESS_DENIED
ERR_AMBIGUOUS_ARGUMENT
ERR_ARG_NOT_ITERABLE
ERR_ASSERTION
ERR_ASYNC_CALLBACK
ERR_ASYNC_TYPE
ERR_BROTLI_COMPRESSION_FAILED
ERR_BROTLI_INVALID_PARAM
ERR_BUFFER_CONTEXT_NOT_AVAILABLE
ERR_BUFFER_OUT_OF_BOUNDS
ERR_BUFFER_TOO_LARGE
ERR_CANNOT_WATCH_SIGINT
ERR_CHILD_CLOSED_BEFORE_REPLY
ERR_CHILD_PROCESS_IPC_REQUIRED
ERR_CHILD_PROCESS_STDIO_MAXBUFFER
ERR_CLOSED_MESSAGE_PORT
ERR_CONSOLE_WRITABLE_STREAM
ERR_CONSTRUCT_CALL_INVALID
ERR_CONSTRUCT_CALL_REQUIRED
ERR_CONTEXT_NOT_INITIALIZED
ERR_CRYPTO_CUSTOM_ENGINE_NOT_SUPPORTED
ERR_CRYPTO_ECDH_INVALID_FORMAT
ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY
ERR_CRYPTO_ENGINE_UNKNOWN
ERR_CRYPTO_FIPS_FORCED
ERR_CRYPTO_FIPS_UNAVAILABLE
ERR_CRYPTO_HASH_FINALIZED
ERR_CRYPTO_HASH_UPDATE_FAILED
ERR_CRYPTO_INCOMPATIBLE_KEY
ERR_CRYPTO_INCOMPATIBLE_KEY_OPTIONS
ERR_CRYPTO_INITIALIZATION_FAILED
ERR_CRYPTO_INVALID_AUTH_TAG
ERR_CRYPTO_INVALID_COUNTER
ERR_CRYPTO_INVALID_CURVE
ERR_CRYPTO_INVALID_DIGEST
ERR_CRYPTO_INVALID_IV
ERR_CRYPTO_INVALID_JWK
ERR_CRYPTO_INVALID_KEY_OBJECT_TYPE
ERR_CRYPTO_INVALID_KEYLEN
ERR_CRYPTO_INVALID_KEYPAIR
ERR_CRYPTO_INVALID_KEYTYPE
ERR_CRYPTO_INVALID_MESSAGELEN
ERR_CRYPTO_INVALID_SCRYPT_PARAMS
ERR_CRYPTO_INVALID_STATE
ERR_CRYPTO_INVALID_TAG_LENGTH
ERR_CRYPTO_JOB_INIT_FAILED
ERR_CRYPTO_JWK_UNSUPPORTED_CURVE
ERR_CRYPTO_JWK_UNSUPPORTED_KEY_TYPE
ERR_CRYPTO_OPERATION_FAILED
ERR_CRYPTO_PBKDF2_ERROR
ERR_CRYPTO_SCRYPT_INVALID_PARAMETER
ERR_CRYPTO_SCRYPT_NOT_SUPPORTED
ERR_CRYPTO_SIGN_KEY_REQUIRED
ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH
ERR_CRYPTO_UNKNOWN_CIPHER
ERR_CRYPTO_UNKNOWN_DH_GROUP
ERR_CRYPTO_UNSUPPORTED_OPERATION
ERR_DEBUGGER_ERROR
ERR_DEBUGGER_STARTUP_ERROR
ERR_DLOPEN_DISABLED
ERR_DLOPEN_FAILED
ERR_DIR_CLOSED
ERR_DIR_CONCURRENT_OPERATION
ERR_DNS_SET_SERVERS_FAILED
ERR_DOMAIN_CALLBACK_NOT_AVAILABLE
ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE
ERR_DUPLICATE_STARTUP_SNAPSHOT_MAIN_FUNCTION
ERR_ENCODING_INVALID_ENCODED_DATA
ERR_ENCODING_NOT_SUPPORTED
ERR_EVAL_ESM_CANNOT_PRINT
ERR_EVENT_RECURSION
ERR_EXECUTION_ENVIRONMENT_NOT_AVAILABLE
ERR_FALSY_VALUE_REJECTION
ERR_FEATURE_UNAVAILABLE_ON_PLATFORM
ERR_FS_CP_DIR_TO_NON_DIR
ERR_FS_CP_EEXIST
ERR_FS_CP_EINVAL
ERR_HTTP_BODY_NOT_ALLOWED
ERR_HTTP_CONTENT_LENGTH_MISMATCH
ERR_FS_CP_FIFO_PIPE
ERR_FS_CP_NON_DIR_TO_DIR
ERR_FS_CP_SOCKET
ERR_FS_CP_SYMLINK_TO_SUBDIRECTORY
ERR_FS_CP_UNKNOWN
ERR_FS_EISDIR
ERR_FS_FILE_TOO_LARGE
ERR_FS_INVALID_SYMLINK_TYPE
ERR_HTTP_HEADERS_SENT
ERR_HTTP_INVALID_HEADER_VALUE
ERR_HTTP_INVALID_STATUS_CODE
ERR_HTTP_REQUEST_TIMEOUT
ERR_HTTP_SOCKET_ASSIGNED
ERR_HTTP_SOCKET_ENCODING
ERR_HTTP_TRAILER_INVALID
ERR_HTTP2_ALTSVC_INVALID_ORIGIN
ERR_HTTP2_ALTSVC_LENGTH
ERR_HTTP2_CONNECT_AUTHORITY
ERR_HTTP2_CONNECT_PATH
ERR_HTTP2_CONNECT_SCHEME
ERR_HTTP2_ERROR
ERR_HTTP2_GOAWAY_SESSION
ERR_HTTP2_HEADER_SINGLE_VALUE
ERR_HTTP2_HEADERS_AFTER_RESPOND
ERR_HTTP2_HEADERS_SENT
ERR_HTTP2_INFO_STATUS_NOT_ALLOWED
ERR_HTTP2_INVALID_CONNECTION_HEADERS
ERR_HTTP2_INVALID_HEADER_VALUE
ERR_HTTP2_INVALID_INFO_STATUS
ERR_HTTP2_INVALID_ORIGIN
ERR_HTTP2_INVALID_PACKED_SETTINGS_LENGTH
ERR_HTTP2_INVALID_PSEUDOHEADER
ERR_HTTP2_INVALID_SESSION
ERR_HTTP2_INVALID_SETTING_VALUE
ERR_HTTP2_INVALID_STREAM
ERR_HTTP2_MAX_PENDING_SETTINGS_ACK
ERR_HTTP2_NESTED_PUSH
ERR_HTTP2_NO_MEM
ERR_HTTP2_NO_SOCKET_MANIPULATION
ERR_HTTP2_ORIGIN_LENGTH
ERR_HTTP2_OUT_OF_STREAMS
ERR_HTTP2_PAYLOAD_FORBIDDEN
ERR_HTTP2_PING_CANCEL
ERR_HTTP2_PING_LENGTH
ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED
ERR_HTTP2_PUSH_DISABLED
ERR_HTTP2_SEND_FILE
ERR_HTTP2_SEND_FILE_NOSEEK
ERR_HTTP2_SESSION_ERROR
ERR_HTTP2_SETTINGS_CANCEL
ERR_HTTP2_SOCKET_BOUND
ERR_HTTP2_SOCKET_UNBOUND
ERR_HTTP2_STATUS_101
ERR_HTTP2_STATUS_INVALID
ERR_HTTP2_STREAM_CANCEL
ERR_HTTP2_STREAM_ERROR
ERR_HTTP2_STREAM_SELF_DEPENDENCY
ERR_HTTP2_TOO_MANY_INVALID_FRAMES
ERR_HTTP2_TRAILERS_ALREADY_SENT
ERR_HTTP2_TRAILERS_NOT_READY
ERR_HTTP2_UNSUPPORTED_PROTOCOL
ERR_ILLEGAL_CONSTRUCTOR
ERR_IMPORT_ASSERTION_TYPE_FAILED
ERR_IMPORT_ASSERTION_TYPE_MISSING
ERR_IMPORT_ASSERTION_TYPE_UNSUPPORTED
ERR_INCOMPATIBLE_OPTION_PAIR
ERR_INPUT_TYPE_NOT_ALLOWED
ERR_INSPECTOR_ALREADY_ACTIVATED
ERR_INSPECTOR_ALREADY_CONNECTED
ERR_INSPECTOR_CLOSED
ERR_INSPECTOR_COMMAND
ERR_INSPECTOR_NOT_ACTIVE
ERR_INSPECTOR_NOT_AVAILABLE
ERR_INSPECTOR_NOT_CONNECTED
ERR_INSPECTOR_NOT_WORKER
ERR_INTERNAL_ASSERTION
ERR_INVALID_ADDRESS_FAMILY
ERR_INVALID_ARG_TYPE
ERR_INVALID_ARG_VALUE
ERR_INVALID_ASYNC_ID
ERR_INVALID_BUFFER_SIZE
ERR_INVALID_CHAR
ERR_INVALID_CURSOR_POS
ERR_INVALID_FD
ERR_INVALID_FD_TYPE
ERR_INVALID_FILE_URL_HOST
ERR_INVALID_FILE_URL_PATH
ERR_INVALID_HANDLE_TYPE
ERR_INVALID_HTTP_TOKEN
ERR_INVALID_IP_ADDRESS
ERR_INVALID_MIME_SYNTAX
ERR_INVALID_MODULE
ERR_INVALID_MODULE_SPECIFIER
ERR_INVALID_OBJECT_DEFINE_PROPERTY
ERR_INVALID_PACKAGE_CONFIG
ERR_INVALID_PACKAGE_TARGET
ERR_INVALID_PERFORMANCE_MARK
ERR_INVALID_PROTOCOL
ERR_INVALID_REPL_EVAL_CONFIG
ERR_INVALID_REPL_INPUT
ERR_INVALID_RETURN_PROPERTY
ERR_INVALID_RETURN_PROPERTY_VALUE
ERR_INVALID_RETURN_VALUE
ERR_INVALID_STATE
ERR_INVALID_SYNC_FORK_INPUT
ERR_INVALID_THIS
ERR_INVALID_TRANSFER_OBJECT
ERR_INVALID_TUPLE
ERR_INVALID_URI
ERR_INVALID_URL
ERR_INVALID_URL_SCHEME
ERR_IPC_CHANNEL_CLOSED
ERR_IPC_DISCONNECTED
ERR_IPC_ONE_PIPE
ERR_IPC_SYNC_FORK
ERR_LOADER_CHAIN_INCOMPLETE
ERR_MANIFEST_ASSERT_INTEGRITY
ERR_MANIFEST_DEPENDENCY_MISSING
ERR_MANIFEST_INTEGRITY_MISMATCH
ERR_MANIFEST_INVALID_RESOURCE_FIELD
ERR_MANIFEST_INVALID_SPECIFIER
ERR_MANIFEST_PARSE_POLICY
ERR_MANIFEST_TDZ
ERR_MANIFEST_UNKNOWN_ONERROR
ERR_MEMORY_ALLOCATION_FAILED
ERR_MESSAGE_TARGET_CONTEXT_UNAVAILABLE
ERR_METHOD_NOT_IMPLEMENTED
ERR_MISSING_ARGS
ERR_MISSING_OPTION
ERR_MISSING_PASSPHRASE
ERR_MISSING_PLATFORM_FOR_WORKER
ERR_MISSING_TRANSFERABLE_IN_TRANSFER_LIST
ERR_MODULE_NOT_FOUND
ERR_MULTIPLE_CALLBACK
ERR_NAPI_CONS_FUNCTION
ERR_NAPI_INVALID_DATAVIEW_ARGS
ERR_NAPI_INVALID_TYPEDARRAY_ALIGNMENT
ERR_NAPI_INVALID_TYPEDARRAY_LENGTH
ERR_NAPI_TSFN_CALL_JS
ERR_NAPI_TSFN_GET_UNDEFINED
ERR_NAPI_TSFN_START_IDLE_LOOP
ERR_NAPI_TSFN_STOP_IDLE_LOOP
ERR_NOT_BUILDING_SNAPSHOT
ERR_NOT_SUPPORTED_IN_SNAPSHOT
ERR_NO_CRYPTO
ERR_NO_ICU
ERR_NON_CONTEXT_AWARE_DISABLED
ERR_OUT_OF_RANGE
ERR_PACKAGE_IMPORT_NOT_DEFINED
ERR_PACKAGE_PATH_NOT_EXPORTED
ERR_PARSE_ARGS_INVALID_OPTION_VALUE
ERR_PARSE_ARGS_UNEXPECTED_POSITIONAL
ERR_PARSE_ARGS_UNKNOWN_OPTION
ERR_PERFORMANCE_INVALID_TIMESTAMP
ERR_PERFORMANCE_MEASURE_INVALID_OPTIONS
ERR_PROTO_ACCESS
ERR_REQUIRE_ESM
ERR_SCRIPT_EXECUTION_INTERRUPTED
ERR_SCRIPT_EXECUTION_TIMEOUT
ERR_SERVER_ALREADY_LISTEN
ERR_SERVER_NOT_RUNNING
ERR_SOCKET_ALREADY_BOUND
ERR_SOCKET_BAD_BUFFER_SIZE
ERR_SOCKET_BAD_PORT
ERR_SOCKET_BAD_TYPE
ERR_SOCKET_BUFFER_SIZE
ERR_SOCKET_CLOSED
ERR_SOCKET_CLOSED_BEFORE_CONNECTION
ERR_SOCKET_CONNECTION_TIMEOUT
ERR_SOCKET_DGRAM_IS_CONNECTED
ERR_SOCKET_DGRAM_NOT_CONNECTED
ERR_SOCKET_DGRAM_NOT_RUNNING
ERR_SRI_PARSE
ERR_STREAM_ALREADY_FINISHED
ERR_STREAM_CANNOT_PIPE
ERR_STREAM_DESTROYED
ERR_STREAM_NULL_VALUES
ERR_STREAM_PREMATURE_CLOSE
ERR_STREAM_PUSH_AFTER_EOF
ERR_STREAM_UNSHIFT_AFTER_END_EVENT
ERR_STREAM_WRAP
ERR_STREAM_WRITE_AFTER_END
ERR_STRING_TOO_LONG
ERR_SYNTHETIC
ERR_SYSTEM_ERROR
ERR_TAP_LEXER_ERROR
ERR_TAP_PARSER_ERROR
ERR_TAP_VALIDATION_ERROR
ERR_TEST_FAILURE
ERR_TLS_ALPN_CALLBACK_INVALID_RESULT
ERR_TLS_ALPN_CALLBACK_WITH_PROTOCOLS
ERR_TLS_CERT_ALTNAME_FORMAT
ERR_TLS_CERT_ALTNAME_INVALID
ERR_TLS_DH_PARAM_SIZE
ERR_TLS_HANDSHAKE_TIMEOUT
ERR_TLS_INVALID_CONTEXT
ERR_TLS_INVALID_PROTOCOL_METHOD
ERR_TLS_INVALID_PROTOCOL_VERSION
ERR_TLS_INVALID_STATE
ERR_TLS_PROTOCOL_VERSION_CONFLICT
ERR_TLS_PSK_SET_IDENTIY_HINT_FAILED
ERR_TLS_RENEGOTIATION_DISABLED
ERR_TLS_REQUIRED_SERVER_NAME
ERR_TLS_SESSION_ATTACK
ERR_TLS_SNI_FROM_SERVER
ERR_TRACE_EVENTS_CATEGORY_REQUIRED
ERR_TRACE_EVENTS_UNAVAILABLE
ERR_TRANSFORM_ALREADY_TRANSFORMING
ERR_TRANSFORM_WITH_LENGTH_0
ERR_TTY_INIT_FAILED
ERR_UNAVAILABLE_DURING_EXIT
ERR_UNCAUGHT_EXCEPTION_CAPTURE_ALREADY_SET
ERR_UNESCAPED_CHARACTERS
ERR_UNHANDLED_ERROR
ERR_UNKNOWN_BUILTIN_MODULE
ERR_UNKNOWN_CREDENTIAL
ERR_UNKNOWN_ENCODING
ERR_UNKNOWN_FILE_EXTENSION
ERR_UNKNOWN_MODULE_FORMAT
ERR_UNKNOWN_SIGNAL
ERR_UNSUPPORTED_DIR_IMPORT
ERR_UNSUPPORTED_ESM_URL_SCHEME
ERR_USE_AFTER_CLOSE
ERR_VALID_PERFORMANCE_ENTRY_TYPE
ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING
ERR_VM_MODULE_ALREADY_LINKED
ERR_VM_MODULE_CACHED_DATA_REJECTED
ERR_VM_MODULE_CANNOT_CREATE_CACHED_DATA
ERR_VM_MODULE_DIFFERENT_CONTEXT
ERR_VM_MODULE_LINK_FAILURE
ERR_VM_MODULE_NOT_MODULE
ERR_VM_MODULE_STATUS
ERR_WASI_ALREADY_STARTED
ERR_WASI_NOT_STARTED
ERR_WEBASSEMBLY_RESPONSE
ERR_WORKER_INIT_FAILED
ERR_WORKER_INVALID_EXEC_ARGV
ERR_WORKER_NOT_RUNNING
ERR_WORKER_OUT_OF_MEMORY
ERR_WORKER_PATH
ERR_WORKER_UNSERIALIZABLE_ERROR
ERR_WORKER_UNSUPPORTED_OPERATION
ERR_ZLIB_INITIALIZATION_FAILED
HPE_HEADER_OVERFLOW
HPE_UNEXPECTED_CONTENT_LENGTH
MODULE_NOT_FOUND
- Legacy Node.js error codes
ERR_CANNOT_TRANSFER_OBJECT
ERR_CRYPTO_HASH_DIGEST_NO_UTF16
ERR_HTTP2_FRAME_ERROR
ERR_HTTP2_HEADERS_OBJECT
ERR_HTTP2_HEADER_REQUIRED
ERR_HTTP2_INFO_HEADERS_AFTER_RESPOND
ERR_HTTP2_STREAM_CLOSED
ERR_HTTP_INVALID_CHAR
ERR_INDEX_OUT_OF_RANGE
ERR_INVALID_OPT_VALUE
ERR_INVALID_OPT_VALUE_ENCODING
ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST
ERR_NAPI_CONS_PROTOTYPE_OBJECT
ERR_NETWORK_IMPORT_BAD_RESPONSE
ERR_NETWORK_IMPORT_DISALLOWED
ERR_NO_LONGER_SUPPORTED
ERR_OPERATION_FAILED
ERR_OUTOFMEMORY
ERR_PARSE_HISTORY_DATA
ERR_SOCKET_CANNOT_SEND
ERR_STDERR_CLOSE
ERR_STDOUT_CLOSE
ERR_STREAM_READ_NOT_IMPLEMENTED
ERR_TLS_RENEGOTIATION_FAILED
ERR_TRANSFERRING_EXTERNALIZED_SHAREDARRAYBUFFER
ERR_UNKNOWN_STDIN_TYPE
ERR_UNKNOWN_STREAM_TYPE
ERR_V8BREAKITERATOR
ERR_VALUE_OUT_OF_RANGE
ERR_VM_MODULE_NOT_LINKED
ERR_VM_MODULE_LINKING_ERRORED
ERR_WORKER_UNSUPPORTED_EXTENSION
ERR_ZLIB_BINDING_CLOSED
ERR_CPU_USAGE
- Events
- Passing arguments and
this
to listeners - Asynchronous vs. synchronous
- Handling events only once
- Error events
- Capture rejections of promises
- Class:
EventEmitter
- Event:
'newListener'
- Event:
'removeListener'
emitter.addListener(eventName, listener)
emitter.emit(eventName[, ...args])
emitter.eventNames()
emitter.getMaxListeners()
emitter.listenerCount(eventName[, listener])
emitter.listeners(eventName)
emitter.off(eventName, listener)
emitter.on(eventName, listener)
emitter.once(eventName, listener)
emitter.prependListener(eventName, listener)
emitter.prependOnceListener(eventName, listener)
emitter.removeAllListeners([eventName])
emitter.removeListener(eventName, listener)
emitter.setMaxListeners(n)
emitter.rawListeners(eventName)
emitter[Symbol.for('nodejs.rejection')](err, eventName[, ...args])
- Event:
events.defaultMaxListeners
events.errorMonitor
events.getEventListeners(emitterOrTarget, eventName)
events.getMaxListeners(emitterOrTarget)
events.once(emitter, name[, options])
events.captureRejections
events.captureRejectionSymbol
events.listenerCount(emitter, eventName)
events.on(emitter, eventName[, options])
events.setMaxListeners(n[, ...eventTargets])
events.addAbortListener(signal, listener)
- Class:
events.EventEmitterAsyncResource extends EventEmitter
EventTarget
andEvent
API- Node.js
EventTarget
vs. DOMEventTarget
NodeEventTarget
vs.EventEmitter
- Event listener
EventTarget
error handling- Class:
Event
event.bubbles
event.cancelBubble
event.cancelable
event.composed
event.composedPath()
event.currentTarget
event.defaultPrevented
event.eventPhase
event.initEvent(type[, bubbles[, cancelable]])
event.isTrusted
event.preventDefault()
event.returnValue
event.srcElement
event.stopImmediatePropagation()
event.stopPropagation()
event.target
event.timeStamp
event.type
- Class:
EventTarget
- Class:
CustomEvent
- Class:
NodeEventTarget
nodeEventTarget.addListener(type, listener)
nodeEventTarget.emit(type, arg)
nodeEventTarget.eventNames()
nodeEventTarget.listenerCount(type)
nodeEventTarget.setMaxListeners(n)
nodeEventTarget.getMaxListeners()
nodeEventTarget.off(type, listener[, options])
nodeEventTarget.on(type, listener)
nodeEventTarget.once(type, listener)
nodeEventTarget.removeAllListeners([type])
nodeEventTarget.removeListener(type, listener[, options])
- Node.js
- Passing arguments and
- File system
- Promise example
- Callback example
- Synchronous example
- Promises API
- Class:
FileHandle
- Event:
'close'
filehandle.appendFile(data[, options])
filehandle.chmod(mode)
filehandle.chown(uid, gid)
filehandle.close()
filehandle.createReadStream([options])
filehandle.createWriteStream([options])
filehandle.datasync()
filehandle.fd
filehandle.read(buffer, offset, length, position)
filehandle.read([options])
filehandle.read(buffer[, options])
filehandle.readableWebStream([options])
filehandle.readFile(options)
filehandle.readLines([options])
filehandle.readv(buffers[, position])
filehandle.stat([options])
filehandle.sync()
filehandle.truncate(len)
filehandle.utimes(atime, mtime)
filehandle.write(buffer, offset[, length[, position]])
filehandle.write(buffer[, options])
filehandle.write(string[, position[, encoding]])
filehandle.writeFile(data, options)
filehandle.writev(buffers[, position])
filehandle[Symbol.asyncDispose]()
- Event:
fsPromises.access(path[, mode])
fsPromises.appendFile(path, data[, options])
fsPromises.chmod(path, mode)
fsPromises.chown(path, uid, gid)
fsPromises.copyFile(src, dest[, mode])
fsPromises.cp(src, dest[, options])
fsPromises.lchmod(path, mode)
fsPromises.lchown(path, uid, gid)
fsPromises.lutimes(path, atime, mtime)
fsPromises.link(existingPath, newPath)
fsPromises.lstat(path[, options])
fsPromises.mkdir(path[, options])
fsPromises.mkdtemp(prefix[, options])
fsPromises.open(path, flags[, mode])
fsPromises.opendir(path[, options])
fsPromises.readdir(path[, options])
fsPromises.readFile(path[, options])
fsPromises.readlink(path[, options])
fsPromises.realpath(path[, options])
fsPromises.rename(oldPath, newPath)
fsPromises.rmdir(path[, options])
fsPromises.rm(path[, options])
fsPromises.stat(path[, options])
fsPromises.statfs(path[, options])
fsPromises.symlink(target, path[, type])
fsPromises.truncate(path[, len])
fsPromises.unlink(path)
fsPromises.utimes(path, atime, mtime)
fsPromises.watch(filename[, options])
fsPromises.writeFile(file, data[, options])
fsPromises.constants
- Class:
- Callback API
fs.access(path[, mode], callback)
fs.appendFile(path, data[, options], callback)
fs.chmod(path, mode, callback)
fs.chown(path, uid, gid, callback)
fs.close(fd[, callback])
fs.copyFile(src, dest[, mode], callback)
fs.cp(src, dest[, options], callback)
fs.createReadStream(path[, options])
fs.createWriteStream(path[, options])
fs.exists(path, callback)
fs.fchmod(fd, mode, callback)
fs.fchown(fd, uid, gid, callback)
fs.fdatasync(fd, callback)
fs.fstat(fd[, options], callback)
fs.fsync(fd, callback)
fs.ftruncate(fd[, len], callback)
fs.futimes(fd, atime, mtime, callback)
fs.lchmod(path, mode, callback)
fs.lchown(path, uid, gid, callback)
fs.lutimes(path, atime, mtime, callback)
fs.link(existingPath, newPath, callback)
fs.lstat(path[, options], callback)
fs.mkdir(path[, options], callback)
fs.mkdtemp(prefix[, options], callback)
fs.open(path[, flags[, mode]], callback)
fs.openAsBlob(path[, options])
fs.opendir(path[, options], callback)
fs.read(fd, buffer, offset, length, position, callback)
fs.read(fd[, options], callback)
fs.read(fd, buffer[, options], callback)
fs.readdir(path[, options], callback)
fs.readFile(path[, options], callback)
fs.readlink(path[, options], callback)
fs.readv(fd, buffers[, position], callback)
fs.realpath(path[, options], callback)
fs.realpath.native(path[, options], callback)
fs.rename(oldPath, newPath, callback)
fs.rmdir(path[, options], callback)
fs.rm(path[, options], callback)
fs.stat(path[, options], callback)
fs.statfs(path[, options], callback)
fs.symlink(target, path[, type], callback)
fs.truncate(path[, len], callback)
fs.unlink(path, callback)
fs.unwatchFile(filename[, listener])
fs.utimes(path, atime, mtime, callback)
fs.watch(filename[, options][, listener])
fs.watchFile(filename[, options], listener)
fs.write(fd, buffer, offset[, length[, position]], callback)
fs.write(fd, buffer[, options], callback)
fs.write(fd, string[, position[, encoding]], callback)
fs.writeFile(file, data[, options], callback)
fs.writev(fd, buffers[, position], callback)
- Synchronous API
fs.accessSync(path[, mode])
fs.appendFileSync(path, data[, options])
fs.chmodSync(path, mode)
fs.chownSync(path, uid, gid)
fs.closeSync(fd)
fs.copyFileSync(src, dest[, mode])
fs.cpSync(src, dest[, options])
fs.existsSync(path)
fs.fchmodSync(fd, mode)
fs.fchownSync(fd, uid, gid)
fs.fdatasyncSync(fd)
fs.fstatSync(fd[, options])
fs.fsyncSync(fd)
fs.ftruncateSync(fd[, len])
fs.futimesSync(fd, atime, mtime)
fs.lchmodSync(path, mode)
fs.lchownSync(path, uid, gid)
fs.lutimesSync(path, atime, mtime)
fs.linkSync(existingPath, newPath)
fs.lstatSync(path[, options])
fs.mkdirSync(path[, options])
fs.mkdtempSync(prefix[, options])
fs.opendirSync(path[, options])
fs.openSync(path[, flags[, mode]])
fs.readdirSync(path[, options])
fs.readFileSync(path[, options])
fs.readlinkSync(path[, options])
fs.readSync(fd, buffer, offset, length[, position])
fs.readSync(fd, buffer[, options])
fs.readvSync(fd, buffers[, position])
fs.realpathSync(path[, options])
fs.realpathSync.native(path[, options])
fs.renameSync(oldPath, newPath)
fs.rmdirSync(path[, options])
fs.rmSync(path[, options])
fs.statSync(path[, options])
fs.statfsSync(path[, options])
fs.symlinkSync(target, path[, type])
fs.truncateSync(path[, len])
fs.unlinkSync(path)
fs.utimesSync(path, atime, mtime)
fs.writeFileSync(file, data[, options])
fs.writeSync(fd, buffer, offset[, length[, position]])
fs.writeSync(fd, buffer[, options])
fs.writeSync(fd, string[, position[, encoding]])
fs.writevSync(fd, buffers[, position])
- Common Objects
- Class:
fs.Dir
- Class:
fs.Dirent
- Class:
fs.FSWatcher
- Class:
fs.StatWatcher
- Class:
fs.ReadStream
- Class:
fs.Stats
stats.isBlockDevice()
stats.isCharacterDevice()
stats.isDirectory()
stats.isFIFO()
stats.isFile()
stats.isSocket()
stats.isSymbolicLink()
stats.dev
stats.ino
stats.mode
stats.nlink
stats.uid
stats.gid
stats.rdev
stats.size
stats.blksize
stats.blocks
stats.atimeMs
stats.mtimeMs
stats.ctimeMs
stats.birthtimeMs
stats.atimeNs
stats.mtimeNs
stats.ctimeNs
stats.birthtimeNs
stats.atime
stats.mtime
stats.ctime
stats.birthtime
- Stat time values
- Class:
fs.StatFs
- Class:
fs.WriteStream
fs.constants
- Class:
- Notes
- Global objects
- Class:
AbortController
- Class:
Blob
- Class:
Buffer
- Class:
ByteLengthQueuingStrategy
__dirname
__filename
atob(data)
BroadcastChannel
btoa(data)
clearImmediate(immediateObject)
clearInterval(intervalObject)
clearTimeout(timeoutObject)
- Class:
CompressionStream
console
- Class:
CountQueuingStrategy
Crypto
crypto
CryptoKey
CustomEvent
- Class:
DecompressionStream
Event
EventTarget
exports
fetch
- Class:
File
- Class
FormData
global
- Class
Headers
MessageChannel
MessageEvent
MessagePort
module
Navigator
navigator
PerformanceEntry
PerformanceMark
PerformanceMeasure
PerformanceObserver
PerformanceObserverEntryList
PerformanceResourceTiming
performance
process
queueMicrotask(callback)
- Class:
ReadableByteStreamController
- Class:
ReadableStream
- Class:
ReadableStreamBYOBReader
- Class:
ReadableStreamBYOBRequest
- Class:
ReadableStreamDefaultController
- Class:
ReadableStreamDefaultReader
require()
Response
Request
setImmediate(callback[, ...args])
setInterval(callback, delay[, ...args])
setTimeout(callback, delay[, ...args])
structuredClone(value[, options])
SubtleCrypto
DOMException
TextDecoder
- Class:
TextDecoderStream
TextEncoder
- Class:
TextEncoderStream
- Class:
TransformStream
- Class:
TransformStreamDefaultController
URL
URLSearchParams
WebAssembly
WebSocket
- Class:
WritableStream
- Class:
WritableStreamDefaultController
- Class:
WritableStreamDefaultWriter
- Class:
- HTTP
- Class:
http.Agent
- Class:
http.ClientRequest
- Event:
'abort'
- Event:
'close'
- Event:
'connect'
- Event:
'continue'
- Event:
'finish'
- Event:
'information'
- Event:
'response'
- Event:
'socket'
- Event:
'timeout'
- Event:
'upgrade'
request.abort()
request.aborted
request.connection
request.cork()
request.end([data[, encoding]][, callback])
request.destroy([error])
request.finished
request.flushHeaders()
request.getHeader(name)
request.getHeaderNames()
request.getHeaders()
request.getRawHeaderNames()
request.hasHeader(name)
request.maxHeadersCount
request.path
request.method
request.host
request.protocol
request.removeHeader(name)
request.reusedSocket
request.setHeader(name, value)
request.setNoDelay([noDelay])
request.setSocketKeepAlive([enable][, initialDelay])
request.setTimeout(timeout[, callback])
request.socket
request.uncork()
request.writableEnded
request.writableFinished
request.write(chunk[, encoding][, callback])
- Event:
- Class:
http.Server
- Event:
'checkContinue'
- Event:
'checkExpectation'
- Event:
'clientError'
- Event:
'close'
- Event:
'connect'
- Event:
'connection'
- Event:
'dropRequest'
- Event:
'request'
- Event:
'upgrade'
server.close([callback])
server.closeAllConnections()
server.closeIdleConnections()
server.headersTimeout
server.listen()
server.listening
server.maxHeadersCount
server.requestTimeout
server.setTimeout([msecs][, callback])
server.maxRequestsPerSocket
server.timeout
server.keepAliveTimeout
server[Symbol.asyncDispose]()
- Event:
- Class:
http.ServerResponse
- Event:
'close'
- Event:
'finish'
response.addTrailers(headers)
response.connection
response.cork()
response.end([data[, encoding]][, callback])
response.finished
response.flushHeaders()
response.getHeader(name)
response.getHeaderNames()
response.getHeaders()
response.hasHeader(name)
response.headersSent
response.removeHeader(name)
response.req
response.sendDate
response.setHeader(name, value)
response.setTimeout(msecs[, callback])
response.socket
response.statusCode
response.statusMessage
response.strictContentLength
response.uncork()
response.writableEnded
response.writableFinished
response.write(chunk[, encoding][, callback])
response.writeContinue()
response.writeEarlyHints(hints[, callback])
response.writeHead(statusCode[, statusMessage][, headers])
response.writeProcessing()
- Event:
- Class:
http.IncomingMessage
- Event:
'aborted'
- Event:
'close'
message.aborted
message.complete
message.connection
message.destroy([error])
message.headers
message.headersDistinct
message.httpVersion
message.method
message.rawHeaders
message.rawTrailers
message.setTimeout(msecs[, callback])
message.socket
message.statusCode
message.statusMessage
message.trailers
message.trailersDistinct
message.url
- Event:
- Class:
http.OutgoingMessage
- Event:
'drain'
- Event:
'finish'
- Event:
'prefinish'
outgoingMessage.addTrailers(headers)
outgoingMessage.appendHeader(name, value)
outgoingMessage.connection
outgoingMessage.cork()
outgoingMessage.destroy([error])
outgoingMessage.end(chunk[, encoding][, callback])
outgoingMessage.flushHeaders()
outgoingMessage.getHeader(name)
outgoingMessage.getHeaderNames()
outgoingMessage.getHeaders()
outgoingMessage.hasHeader(name)
outgoingMessage.headersSent
outgoingMessage.pipe()
outgoingMessage.removeHeader(name)
outgoingMessage.setHeader(name, value)
outgoingMessage.setHeaders(headers)
outgoingMessage.setTimeout(msesc[, callback])
outgoingMessage.socket
outgoingMessage.uncork()
outgoingMessage.writableCorked
outgoingMessage.writableEnded
outgoingMessage.writableFinished
outgoingMessage.writableHighWaterMark
outgoingMessage.writableLength
outgoingMessage.writableObjectMode
outgoingMessage.write(chunk[, encoding][, callback])
- Event:
http.METHODS
http.STATUS_CODES
http.createServer([options][, requestListener])
http.get(options[, callback])
http.get(url[, options][, callback])
http.globalAgent
http.maxHeaderSize
http.request(options[, callback])
http.request(url[, options][, callback])
http.validateHeaderName(name[, label])
http.validateHeaderValue(name, value)
http.setMaxIdleHTTPParsers(max)
- Class:
- HTTP/2
- Determining if crypto support is unavailable
- Core API
- Server-side example
- Client-side example
- Class:
Http2Session
Http2Session
and sockets- Event:
'close'
- Event:
'connect'
- Event:
'error'
- Event:
'frameError'
- Event:
'goaway'
- Event:
'localSettings'
- Event:
'ping'
- Event:
'remoteSettings'
- Event:
'stream'
- Event:
'timeout'
http2session.alpnProtocol
http2session.close([callback])
http2session.closed
http2session.connecting
http2session.destroy([error][, code])
http2session.destroyed
http2session.encrypted
http2session.goaway([code[, lastStreamID[, opaqueData]]])
http2session.localSettings
http2session.originSet
http2session.pendingSettingsAck
http2session.ping([payload, ]callback)
http2session.ref()
http2session.remoteSettings
http2session.setLocalWindowSize(windowSize)
http2session.setTimeout(msecs, callback)
http2session.socket
http2session.state
http2session.settings([settings][, callback])
http2session.type
http2session.unref()
- Class:
ServerHttp2Session
- Class:
ClientHttp2Session
- Class:
Http2Stream
Http2Stream
Lifecycle- Event:
'aborted'
- Event:
'close'
- Event:
'error'
- Event:
'frameError'
- Event:
'ready'
- Event:
'timeout'
- Event:
'trailers'
- Event:
'wantTrailers'
http2stream.aborted
http2stream.bufferSize
http2stream.close(code[, callback])
http2stream.closed
http2stream.destroyed
http2stream.endAfterHeaders
http2stream.id
http2stream.pending
http2stream.priority(options)
http2stream.rstCode
http2stream.sentHeaders
http2stream.sentInfoHeaders
http2stream.sentTrailers
http2stream.session
http2stream.setTimeout(msecs, callback)
http2stream.state
http2stream.sendTrailers(headers)
- Class:
ClientHttp2Stream
- Class:
ServerHttp2Stream
- Class:
Http2Server
- Class:
Http2SecureServer
http2.createServer([options][, onRequestHandler])
http2.createSecureServer(options[, onRequestHandler])
http2.connect(authority[, options][, listener])
http2.constants
http2.getDefaultSettings()
http2.getPackedSettings([settings])
http2.getUnpackedSettings(buf)
http2.sensitiveHeaders
- Headers object
- Settings object
- Error handling
- Invalid character handling in header names and values
- Push streams on the client
- Supporting the
CONNECT
method - The extended
CONNECT
protocol
- Compatibility API
- ALPN negotiation
- Class:
http2.Http2ServerRequest
- Event:
'aborted'
- Event:
'close'
request.aborted
request.authority
request.complete
request.connection
request.destroy([error])
request.headers
request.httpVersion
request.method
request.rawHeaders
request.rawTrailers
request.scheme
request.setTimeout(msecs, callback)
request.socket
request.stream
request.trailers
request.url
- Event:
- Class:
http2.Http2ServerResponse
- Event:
'close'
- Event:
'finish'
response.addTrailers(headers)
response.connection
response.createPushResponse(headers, callback)
response.end([data[, encoding]][, callback])
response.finished
response.getHeader(name)
response.getHeaderNames()
response.getHeaders()
response.hasHeader(name)
response.headersSent
response.removeHeader(name)
response.req
response.sendDate
response.setHeader(name, value)
response.setTimeout(msecs[, callback])
response.socket
response.statusCode
response.statusMessage
response.stream
response.writableEnded
response.write(chunk[, encoding][, callback])
response.writeContinue()
response.writeEarlyHints(hints)
response.writeHead(statusCode[, statusMessage][, headers])
- Event:
- Collecting HTTP/2 performance metrics
- Note on
:authority
andhost
- HTTPS
- Inspector
- Internationalization support
- Modules: CommonJS modules
- Enabling
- Accessing the main module
- Package manager tips
- The
.mjs
extension - All together
- Caching
- Core modules
- Cycles
- File modules
- Folders as modules
- Loading from
node_modules
folders - Loading from the global folders
- The module wrapper
- The module scope
- The
module
object - The
Module
object - Source map v3 support
- Modules: ECMAScript modules
- Modules:
node:module
API - Modules: Packages
- Net
- IPC support
- Class:
net.BlockList
- Class:
net.SocketAddress
- Class:
net.Server
new net.Server([options][, connectionListener])
- Event:
'close'
- Event:
'connection'
- Event:
'error'
- Event:
'listening'
- Event:
'drop'
server.address()
server.close([callback])
server[Symbol.asyncDispose]()
server.getConnections(callback)
server.listen()
server.listening
server.maxConnections
server.ref()
server.unref()
- Class:
net.Socket
new net.Socket([options])
- Event:
'close'
- Event:
'connect'
- Event:
'data'
- Event:
'drain'
- Event:
'end'
- Event:
'error'
- Event:
'lookup'
- Event:
'ready'
- Event:
'timeout'
socket.address()
socket.autoSelectFamilyAttemptedAddresses
socket.bufferSize
socket.bytesRead
socket.bytesWritten
socket.connect()
socket.connecting
socket.destroy([error])
socket.destroyed
socket.destroySoon()
socket.end([data[, encoding]][, callback])
socket.localAddress
socket.localPort
socket.localFamily
socket.pause()
socket.pending
socket.ref()
socket.remoteAddress
socket.remoteFamily
socket.remotePort
socket.resetAndDestroy()
socket.resume()
socket.setEncoding([encoding])
socket.setKeepAlive([enable][, initialDelay])
socket.setNoDelay([noDelay])
socket.setTimeout(timeout[, callback])
socket.timeout
socket.unref()
socket.write(data[, encoding][, callback])
socket.readyState
net.connect()
net.createConnection()
net.createServer([options][, connectionListener])
net.getDefaultAutoSelectFamily()
net.setDefaultAutoSelectFamily(value)
net.getDefaultAutoSelectFamilyAttemptTimeout()
net.setDefaultAutoSelectFamilyAttemptTimeout(value)
net.isIP(input)
net.isIPv4(input)
net.isIPv6(input)
- OS
os.EOL
os.availableParallelism()
os.arch()
os.constants
os.cpus()
os.devNull
os.endianness()
os.freemem()
os.getPriority([pid])
os.homedir()
os.hostname()
os.loadavg()
os.machine()
os.networkInterfaces()
os.platform()
os.release()
os.setPriority([pid, ]priority)
os.tmpdir()
os.totalmem()
os.type()
os.uptime()
os.userInfo([options])
os.version()
- OS constants
- Path
- Windows vs. POSIX
path.basename(path[, suffix])
path.delimiter
path.dirname(path)
path.extname(path)
path.format(pathObject)
path.isAbsolute(path)
path.join([...paths])
path.normalize(path)
path.parse(path)
path.posix
path.relative(from, to)
path.resolve([...paths])
path.sep
path.toNamespacedPath(path)
path.win32
- Performance measurement APIs
perf_hooks.performance
performance.clearMarks([name])
performance.clearMeasures([name])
performance.clearResourceTimings([name])
performance.eventLoopUtilization([utilization1[, utilization2]])
performance.getEntries()
performance.getEntriesByName(name[, type])
performance.getEntriesByType(type)
performance.mark(name[, options])
performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)
performance.measure(name[, startMarkOrOptions[, endMark]])
performance.nodeTiming
performance.now()
performance.setResourceTimingBufferSize(maxSize)
performance.timeOrigin
performance.timerify(fn[, options])
performance.toJSON()
- Class:
PerformanceEntry
- Class:
PerformanceMark
- Class:
PerformanceMeasure
- Class:
PerformanceNodeEntry
- Class:
PerformanceNodeTiming
- Class:
PerformanceResourceTiming
performanceResourceTiming.workerStart
performanceResourceTiming.redirectStart
performanceResourceTiming.redirectEnd
performanceResourceTiming.fetchStart
performanceResourceTiming.domainLookupStart
performanceResourceTiming.domainLookupEnd
performanceResourceTiming.connectStart
performanceResourceTiming.connectEnd
performanceResourceTiming.secureConnectionStart
performanceResourceTiming.requestStart
performanceResourceTiming.responseEnd
performanceResourceTiming.transferSize
performanceResourceTiming.encodedBodySize
performanceResourceTiming.decodedBodySize
performanceResourceTiming.toJSON()
- Class:
PerformanceObserver
- Class:
PerformanceObserverEntryList
perf_hooks.createHistogram([options])
perf_hooks.monitorEventLoopDelay([options])
- Class:
Histogram
histogram.count
histogram.countBigInt
histogram.exceeds
histogram.exceedsBigInt
histogram.max
histogram.maxBigInt
histogram.mean
histogram.min
histogram.minBigInt
histogram.percentile(percentile)
histogram.percentileBigInt(percentile)
histogram.percentiles
histogram.percentilesBigInt
histogram.reset()
histogram.stddev
- Class:
IntervalHistogram extends Histogram
- Class:
RecordableHistogram extends Histogram
- Examples
- Permissions
- Process
- Process events
process.abort()
process.allowedNodeEnvironmentFlags
process.arch
process.argv
process.argv0
process.channel
process.chdir(directory)
process.config
process.connected
process.constrainedMemory()
process.cpuUsage([previousValue])
process.cwd()
process.debugPort
process.disconnect()
process.dlopen(module, filename[, flags])
process.emitWarning(warning[, options])
process.emitWarning(warning[, type[, code]][, ctor])
process.env
process.execArgv
process.execPath
process.exit([code])
process.exitCode
process.getActiveResourcesInfo()
process.getegid()
process.geteuid()
process.getgid()
process.getgroups()
process.getuid()
process.hasUncaughtExceptionCaptureCallback()
process.hrtime([time])
process.hrtime.bigint()
process.initgroups(user, extraGroup)
process.kill(pid[, signal])
process.mainModule
process.memoryUsage()
process.memoryUsage.rss()
process.nextTick(callback[, ...args])
process.noDeprecation
process.permission
process.pid
process.platform
process.ppid
process.release
process.report
process.resourceUsage()
process.send(message[, sendHandle[, options]][, callback])
process.setegid(id)
process.seteuid(id)
process.setgid(id)
process.setgroups(groups)
process.setuid(id)
process.setSourceMapsEnabled(val)
process.setUncaughtExceptionCaptureCallback(fn)
process.sourceMapsEnabled
process.stderr
process.stdin
process.stdout
process.throwDeprecation
process.title
process.traceDeprecation
process.umask()
process.umask(mask)
process.uptime()
process.version
process.versions
- Exit codes
- Punycode
- Query string
- Readline
- Class:
InterfaceConstructor
- Event:
'close'
- Event:
'line'
- Event:
'history'
- Event:
'pause'
- Event:
'resume'
- Event:
'SIGCONT'
- Event:
'SIGINT'
- Event:
'SIGTSTP'
rl.close()
rl.pause()
rl.prompt([preserveCursor])
rl.resume()
rl.setPrompt(prompt)
rl.getPrompt()
rl.write(data[, key])
rl[Symbol.asyncIterator]()
rl.line
rl.cursor
rl.getCursorPos()
- Event:
- Promises API
- Callback API
readline.emitKeypressEvents(stream[, interface])
- Example: Tiny CLI
- Example: Read file stream line-by-Line
- TTY keybindings
- Class:
- REPL
- Diagnostic report
- Single executable applications
- Stream
- Organization of this document
- Types of streams
- API for stream consumers
- Writable streams
- Class:
stream.Writable
- Event:
'close'
- Event:
'drain'
- Event:
'error'
- Event:
'finish'
- Event:
'pipe'
- Event:
'unpipe'
writable.cork()
writable.destroy([error])
writable.closed
writable.destroyed
writable.end([chunk[, encoding]][, callback])
writable.setDefaultEncoding(encoding)
writable.uncork()
writable.writable
writable.writableAborted
writable.writableEnded
writable.writableCorked
writable.errored
writable.writableFinished
writable.writableHighWaterMark
writable.writableLength
writable.writableNeedDrain
writable.writableObjectMode
writable.write(chunk[, encoding][, callback])
- Event:
- Class:
- Readable streams
- Two reading modes
- Three states
- Choose one API style
- Class:
stream.Readable
- Event:
'close'
- Event:
'data'
- Event:
'end'
- Event:
'error'
- Event:
'pause'
- Event:
'readable'
- Event:
'resume'
readable.destroy([error])
readable.closed
readable.destroyed
readable.isPaused()
readable.pause()
readable.pipe(destination[, options])
readable.read([size])
readable.readable
readable.readableAborted
readable.readableDidRead
readable.readableEncoding
readable.readableEnded
readable.errored
readable.readableFlowing
readable.readableHighWaterMark
readable.readableLength
readable.readableObjectMode
readable.resume()
readable.setEncoding(encoding)
readable.unpipe([destination])
readable.unshift(chunk[, encoding])
readable.wrap(stream)
readable[Symbol.asyncIterator]()
readable[Symbol.asyncDispose]()
readable.compose(stream[, options])
readable.iterator([options])
readable.map(fn[, options])
readable.filter(fn[, options])
readable.forEach(fn[, options])
readable.toArray([options])
readable.some(fn[, options])
readable.find(fn[, options])
readable.every(fn[, options])
readable.flatMap(fn[, options])
readable.drop(limit[, options])
readable.take(limit[, options])
readable.reduce(fn[, initial[, options]])
- Event:
- Duplex and transform streams
stream.finished(stream[, options], callback)
stream.pipeline(source[, ...transforms], destination, callback)
stream.pipeline(streams, callback)
stream.compose(...streams)
stream.Readable.from(iterable[, options])
stream.Readable.fromWeb(readableStream[, options])
stream.Readable.isDisturbed(stream)
stream.isErrored(stream)
stream.isReadable(stream)
stream.Readable.toWeb(streamReadable[, options])
stream.Writable.fromWeb(writableStream[, options])
stream.Writable.toWeb(streamWritable)
stream.Duplex.from(src)
stream.Duplex.fromWeb(pair[, options])
stream.Duplex.toWeb(streamDuplex)
stream.addAbortSignal(signal, stream)
stream.getDefaultHighWaterMark(objectMode)
stream.setDefaultHighWaterMark(objectMode, value)
- Writable streams
- API for stream implementers
- Additional notes
- String decoder
- Test runner
- Subtests
- Skipping tests
describe
/it
syntaxonly
tests- Filtering tests by name
- Extraneous asynchronous activity
- Watch mode
- Running tests from the command line
- Collecting code coverage
- Mocking
- Test reporters
run([options])
test([name][, options][, fn])
test.skip([name][, options][, fn])
test.todo([name][, options][, fn])
test.only([name][, options][, fn])
describe([name][, options][, fn])
describe.skip([name][, options][, fn])
describe.todo([name][, options][, fn])
describe.only([name][, options][, fn])
it([name][, options][, fn])
it.skip([name][, options][, fn])
it.todo([name][, options][, fn])
it.only([name][, options][, fn])
before([fn][, options])
after([fn][, options])
beforeEach([fn][, options])
afterEach([fn][, options])
- Class:
MockFunctionContext
- Class:
MockTracker
- Class:
MockTimers
- Class:
TestsStream
- Class:
TestContext
context.before([fn][, options])
context.beforeEach([fn][, options])
context.after([fn][, options])
context.afterEach([fn][, options])
context.diagnostic(message)
context.name
context.runOnly(shouldRunOnlyTests)
context.signal
context.skip([message])
context.todo([message])
context.test([name][, options][, fn])
- Class:
SuiteContext
- Timers
- TLS (SSL)
- Determining if crypto support is unavailable
- TLS/SSL concepts
- Modifying the default TLS cipher suite
- X509 certificate error codes
- Class:
tls.CryptoStream
- Class:
tls.SecurePair
- Class:
tls.Server
- Event:
'connection'
- Event:
'keylog'
- Event:
'newSession'
- Event:
'OCSPRequest'
- Event:
'resumeSession'
- Event:
'secureConnection'
- Event:
'tlsClientError'
server.addContext(hostname, context)
server.address()
server.close([callback])
server.getTicketKeys()
server.listen()
server.setSecureContext(options)
server.setTicketKeys(keys)
- Event:
- Class:
tls.TLSSocket
new tls.TLSSocket(socket[, options])
- Event:
'keylog'
- Event:
'OCSPResponse'
- Event:
'secureConnect'
- Event:
'session'
tlsSocket.address()
tlsSocket.authorizationError
tlsSocket.authorized
tlsSocket.disableRenegotiation()
tlsSocket.enableTrace()
tlsSocket.encrypted
tlsSocket.exportKeyingMaterial(length, label[, context])
tlsSocket.getCertificate()
tlsSocket.getCipher()
tlsSocket.getEphemeralKeyInfo()
tlsSocket.getFinished()
tlsSocket.getPeerCertificate([detailed])
tlsSocket.getPeerFinished()
tlsSocket.getPeerX509Certificate()
tlsSocket.getProtocol()
tlsSocket.getSession()
tlsSocket.getSharedSigalgs()
tlsSocket.getTLSTicket()
tlsSocket.getX509Certificate()
tlsSocket.isSessionReused()
tlsSocket.localAddress
tlsSocket.localPort
tlsSocket.remoteAddress
tlsSocket.remoteFamily
tlsSocket.remotePort
tlsSocket.renegotiate(options, callback)
tlsSocket.setMaxSendFragment(size)
tls.checkServerIdentity(hostname, cert)
tls.connect(options[, callback])
tls.connect(path[, options][, callback])
tls.connect(port[, host][, options][, callback])
tls.createSecureContext([options])
tls.createSecurePair([context][, isServer][, requestCert][, rejectUnauthorized][, options])
tls.createServer([options][, secureConnectionListener])
tls.getCiphers()
tls.rootCertificates
tls.DEFAULT_ECDH_CURVE
tls.DEFAULT_MAX_VERSION
tls.DEFAULT_MIN_VERSION
tls.DEFAULT_CIPHERS
- Trace events
- TTY
- Class:
tty.ReadStream
- Class:
tty.WriteStream
- Event:
'resize'
writeStream.clearLine(dir[, callback])
writeStream.clearScreenDown([callback])
writeStream.columns
writeStream.cursorTo(x[, y][, callback])
writeStream.getColorDepth([env])
writeStream.getWindowSize()
writeStream.hasColors([count][, env])
writeStream.isTTY
writeStream.moveCursor(dx, dy[, callback])
writeStream.rows
- Event:
tty.isatty(fd)
- Class:
- UDP/datagram sockets
- Class:
dgram.Socket
- Event:
'close'
- Event:
'connect'
- Event:
'error'
- Event:
'listening'
- Event:
'message'
socket.addMembership(multicastAddress[, multicastInterface])
socket.addSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
socket.address()
socket.bind([port][, address][, callback])
socket.bind(options[, callback])
socket.close([callback])
socket[Symbol.asyncDispose]()
socket.connect(port[, address][, callback])
socket.disconnect()
socket.dropMembership(multicastAddress[, multicastInterface])
socket.dropSourceSpecificMembership(sourceAddress, groupAddress[, multicastInterface])
socket.getRecvBufferSize()
socket.getSendBufferSize()
socket.getSendQueueSize()
socket.getSendQueueCount()
socket.ref()
socket.remoteAddress()
socket.send(msg[, offset, length][, port][, address][, callback])
socket.setBroadcast(flag)
socket.setMulticastInterface(multicastInterface)
socket.setMulticastLoopback(flag)
socket.setMulticastTTL(ttl)
socket.setRecvBufferSize(size)
socket.setSendBufferSize(size)
socket.setTTL(ttl)
socket.unref()
- Event:
node:dgram
module functions
- Class:
- URL
- URL strings and URL objects
- The WHATWG URL API
- Class:
URL
- Class:
URLSearchParams
new URLSearchParams()
new URLSearchParams(string)
new URLSearchParams(obj)
new URLSearchParams(iterable)
urlSearchParams.append(name, value)
urlSearchParams.delete(name[, value])
urlSearchParams.entries()
urlSearchParams.forEach(fn[, thisArg])
urlSearchParams.get(name)
urlSearchParams.getAll(name)
urlSearchParams.has(name[, value])
urlSearchParams.keys()
urlSearchParams.set(name, value)
urlSearchParams.size
urlSearchParams.sort()
urlSearchParams.toString()
urlSearchParams.values()
urlSearchParams[Symbol.iterator]()
url.domainToASCII(domain)
url.domainToUnicode(domain)
url.fileURLToPath(url)
url.format(URL[, options])
url.pathToFileURL(path)
url.urlToHttpOptions(url)
- Class:
- Legacy URL API
- Percent-encoding in URLs
- Util
util.callbackify(original)
util.debuglog(section[, callback])
util.debug(section)
util.deprecate(fn, msg[, code])
util.format(format[, ...args])
util.formatWithOptions(inspectOptions, format[, ...args])
util.getSystemErrorName(err)
util.getSystemErrorMap()
util.inherits(constructor, superConstructor)
util.inspect(object[, options])
util.inspect(object[, showHidden[, depth[, colors]]])
util.isDeepStrictEqual(val1, val2)
- Class:
util.MIMEType
- Class:
util.MIMEParams
util.parseArgs([config])
util.promisify(original)
util.stripVTControlCharacters(str)
- Class:
util.TextDecoder
- Class:
util.TextEncoder
util.toUSVString(string)
util.transferableAbortController()
util.transferableAbortSignal(signal)
util.aborted(signal, resource)
util.types
util.types.isAnyArrayBuffer(value)
util.types.isArrayBufferView(value)
util.types.isArgumentsObject(value)
util.types.isArrayBuffer(value)
util.types.isAsyncFunction(value)
util.types.isBigInt64Array(value)
util.types.isBigUint64Array(value)
util.types.isBooleanObject(value)
util.types.isBoxedPrimitive(value)
util.types.isCryptoKey(value)
util.types.isDataView(value)
util.types.isDate(value)
util.types.isExternal(value)
util.types.isFloat32Array(value)
util.types.isFloat64Array(value)
util.types.isGeneratorFunction(value)
util.types.isGeneratorObject(value)
util.types.isInt8Array(value)
util.types.isInt16Array(value)
util.types.isInt32Array(value)
util.types.isKeyObject(value)
util.types.isMap(value)
util.types.isMapIterator(value)
util.types.isModuleNamespaceObject(value)
util.types.isNativeError(value)
util.types.isNumberObject(value)
util.types.isPromise(value)
util.types.isProxy(value)
util.types.isRegExp(value)
util.types.isSet(value)
util.types.isSetIterator(value)
util.types.isSharedArrayBuffer(value)
util.types.isStringObject(value)
util.types.isSymbolObject(value)
util.types.isTypedArray(value)
util.types.isUint8Array(value)
util.types.isUint8ClampedArray(value)
util.types.isUint16Array(value)
util.types.isUint32Array(value)
util.types.isWeakMap(value)
util.types.isWeakSet(value)
util.types.isWebAssemblyCompiledModule(value)
- Deprecated APIs
util._extend(target, source)
util.isArray(object)
util.isBoolean(object)
util.isBuffer(object)
util.isDate(object)
util.isError(object)
util.isFunction(object)
util.isNull(object)
util.isNullOrUndefined(object)
util.isNumber(object)
util.isObject(object)
util.isPrimitive(object)
util.isRegExp(object)
util.isString(object)
util.isSymbol(object)
util.isUndefined(object)
util.log(string)
- V8
v8.cachedDataVersionTag()
v8.getHeapCodeStatistics()
v8.getHeapSnapshot([options])
v8.getHeapSpaceStatistics()
v8.getHeapStatistics()
v8.setFlagsFromString(flags)
v8.stopCoverage()
v8.takeCoverage()
v8.writeHeapSnapshot([filename[,options]])
v8.setHeapSnapshotNearHeapLimit(limit)
- Serialization API
v8.serialize(value)
v8.deserialize(buffer)
- Class:
v8.Serializer
new Serializer()
serializer.writeHeader()
serializer.writeValue(value)
serializer.releaseBuffer()
serializer.transferArrayBuffer(id, arrayBuffer)
serializer.writeUint32(value)
serializer.writeUint64(hi, lo)
serializer.writeDouble(value)
serializer.writeRawBytes(buffer)
serializer._writeHostObject(object)
serializer._getDataCloneError(message)
serializer._getSharedArrayBufferId(sharedArrayBuffer)
serializer._setTreatArrayBufferViewsAsHostObjects(flag)
- Class:
v8.Deserializer
new Deserializer(buffer)
deserializer.readHeader()
deserializer.readValue()
deserializer.transferArrayBuffer(id, arrayBuffer)
deserializer.getWireFormatVersion()
deserializer.readUint32()
deserializer.readUint64()
deserializer.readDouble()
deserializer.readRawBytes(length)
deserializer._readHostObject()
- Class:
v8.DefaultSerializer
- Class:
v8.DefaultDeserializer
- Promise hooks
- Startup Snapshot API
- Class:
v8.GCProfiler
- VM (executing JavaScript)
- Class:
vm.Script
- Class:
vm.Module
- Class:
vm.SourceTextModule
- Class:
vm.SyntheticModule
vm.compileFunction(code[, params[, options]])
vm.createContext([contextObject[, options]])
vm.isContext(object)
vm.measureMemory([options])
vm.runInContext(code, contextifiedObject[, options])
vm.runInNewContext(code[, contextObject[, options]])
vm.runInThisContext(code[, options])
- Example: Running an HTTP server within a VM
- What does it mean to "contextify" an object?
- Timeout interactions with asynchronous tasks and Promises
- Class:
- WebAssembly System Interface (WASI)
- Web Crypto API
- Examples
- Algorithm matrix
- Class:
Crypto
- Class:
CryptoKey
- Class:
CryptoKeyPair
- Class:
SubtleCrypto
subtle.decrypt(algorithm, key, data)
subtle.deriveBits(algorithm, baseKey, length)
subtle.deriveKey(algorithm, baseKey, derivedKeyAlgorithm, extractable, keyUsages)
subtle.digest(algorithm, data)
subtle.encrypt(algorithm, key, data)
subtle.exportKey(format, key)
subtle.generateKey(algorithm, extractable, keyUsages)
subtle.importKey(format, keyData, algorithm, extractable, keyUsages)
subtle.sign(algorithm, key, data)
subtle.unwrapKey(format, wrappedKey, unwrappingKey, unwrapAlgo, unwrappedKeyAlgo, extractable, keyUsages)
subtle.verify(algorithm, key, signature, data)
subtle.wrapKey(format, key, wrappingKey, wrapAlgo)
- Algorithm parameters
- Class:
AlgorithmIdentifier
- Class:
AesCbcParams
- Class:
AesCtrParams
- Class:
AesGcmParams
- Class:
AesKeyGenParams
- Class:
EcdhKeyDeriveParams
- Class:
EcdsaParams
- Class:
EcKeyGenParams
- Class:
EcKeyImportParams
- Class:
Ed448Params
- Class:
HkdfParams
- Class:
HmacImportParams
- Class:
HmacKeyGenParams
- Class:
Pbkdf2Params
- Class:
RsaHashedImportParams
- Class:
RsaHashedKeyGenParams
- Class:
RsaOaepParams
- Class:
RsaPssParams
- Class:
- Web Streams API
- Overview
- API
- Class:
ReadableStream
new ReadableStream([underlyingSource [, strategy]])
readableStream.locked
readableStream.cancel([reason])
readableStream.getReader([options])
readableStream.pipeThrough(transform[, options])
readableStream.pipeTo(destination[, options])
readableStream.tee()
readableStream.values([options])
- Async Iteration
- Transferring with
postMessage()
ReadableStream.from(iterable)
- Class:
ReadableStreamDefaultReader
- Class:
ReadableStreamBYOBReader
- Class:
ReadableStreamDefaultController
- Class:
ReadableByteStreamController
- Class:
ReadableStreamBYOBRequest
- Class:
WritableStream
- Class:
WritableStreamDefaultWriter
new WritableStreamDefaultWriter(stream)
writableStreamDefaultWriter.abort([reason])
writableStreamDefaultWriter.close()
writableStreamDefaultWriter.closed
writableStreamDefaultWriter.desiredSize
writableStreamDefaultWriter.ready
writableStreamDefaultWriter.releaseLock()
writableStreamDefaultWriter.write([chunk])
- Class:
WritableStreamDefaultController
- Class:
TransformStream
- Class:
TransformStreamDefaultController
- Class:
ByteLengthQueuingStrategy
- Class:
CountQueuingStrategy
- Class:
TextEncoderStream
- Class:
TextDecoderStream
- Class:
CompressionStream
- Class:
DecompressionStream
- Utility Consumers
- Class:
- Worker threads
worker.getEnvironmentData(key)
worker.isMainThread
worker.markAsUntransferable(object)
worker.isMarkedAsUntransferable(object)
worker.moveMessagePortToContext(port, contextifiedSandbox)
worker.parentPort
worker.receiveMessageOnPort(port)
worker.resourceLimits
worker.SHARE_ENV
worker.setEnvironmentData(key[, value])
worker.threadId
worker.workerData
- Class:
BroadcastChannel extends EventTarget
- Class:
MessageChannel
- Class:
MessagePort
- Class:
Worker
new Worker(filename[, options])
- Event:
'error'
- Event:
'exit'
- Event:
'message'
- Event:
'messageerror'
- Event:
'online'
worker.getHeapSnapshot([options])
worker.performance
worker.postMessage(value[, transferList])
worker.ref()
worker.resourceLimits
worker.stderr
worker.stdin
worker.stdout
worker.terminate()
worker.threadId
worker.unref()
- Notes
- Zlib
- Threadpool usage and performance considerations
- Compressing HTTP requests and responses
- Memory usage tuning
- Flushing
- Constants
- Class:
Options
- Class:
BrotliOptions
- Class:
zlib.BrotliCompress
- Class:
zlib.BrotliDecompress
- Class:
zlib.Deflate
- Class:
zlib.DeflateRaw
- Class:
zlib.Gunzip
- Class:
zlib.Gzip
- Class:
zlib.Inflate
- Class:
zlib.InflateRaw
- Class:
zlib.Unzip
- Class:
zlib.ZlibBase
zlib.constants
zlib.createBrotliCompress([options])
zlib.createBrotliDecompress([options])
zlib.createDeflate([options])
zlib.createDeflateRaw([options])
zlib.createGunzip([options])
zlib.createGzip([options])
zlib.createInflate([options])
zlib.createInflateRaw([options])
zlib.createUnzip([options])
- Convenience methods
zlib.brotliCompress(buffer[, options], callback)
zlib.brotliCompressSync(buffer[, options])
zlib.brotliDecompress(buffer[, options], callback)
zlib.brotliDecompressSync(buffer[, options])
zlib.deflate(buffer[, options], callback)
zlib.deflateSync(buffer[, options])
zlib.deflateRaw(buffer[, options], callback)
zlib.deflateRawSync(buffer[, options])
zlib.gunzip(buffer[, options], callback)
zlib.gunzipSync(buffer[, options])
zlib.gzip(buffer[, options], callback)
zlib.gzipSync(buffer[, options])
zlib.inflate(buffer[, options], callback)
zlib.inflateSync(buffer[, options])
zlib.inflateRaw(buffer[, options], callback)
zlib.inflateRawSync(buffer[, options])
zlib.unzip(buffer[, options], callback)
zlib.unzipSync(buffer[, options])
About this documentation#
Welcome to the official API reference documentation for Node.js!
Node.js is a JavaScript runtime built on the V8 JavaScript engine.
Contributing#
Report errors in this documentation in the issue tracker. See the contributing guide for directions on how to submit pull requests.
Stability index#
Throughout the documentation are indications of a section's stability. Some APIs are so proven and so relied upon that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous.
The stability indices are as follows:
Experimental features are subdivided into stages:
- 1.0 - Early development. Experimental features at this stage are unfinished and subject to substantial change.
- 1.1 - Active development. Experimental features at this stage are nearing minimum viability.
- 1.2 - Release candidate. Experimental features at this stage are hopefully ready to become stable. No further breaking changes are anticipated but may still occur in response to user feedback. We encourage user testing and feedback so that we can know that this feature is ready to be marked as stable.
Features are marked as legacy rather than being deprecated if their use does no harm, and they are widely relied upon within the npm ecosystem. Bugs found in legacy features are unlikely to be fixed.
Use caution when making use of Experimental features, particularly when authoring libraries. Users may not be aware that experimental features are being used. Bugs or behavior changes may surprise users when Experimental API modifications occur. To avoid surprises, use of an Experimental feature may need a command-line flag. Experimental features may also emit a warning.
Stability overview#
JSON output#
Every .html
document has a corresponding .json
document. This is for IDEs
and other utilities that consume the documentation.
System calls and man pages#
Node.js functions which wrap a system call will document that. The docs link to the corresponding man pages which describe how the system call works.
Most Unix system calls have Windows analogues. Still, behavior differences may be unavoidable.
Usage and example#
Usage#
node [options] [V8 options] [script.js | -e "script" | - ] [arguments]
Please see the Command-line options document for more information.
Example#
An example of a web server written with Node.js which responds with
'Hello, World!'
:
Commands in this document start with $
or >
to replicate how they would
appear in a user's terminal. Do not include the $
and >
characters. They are
there to show the start of each command.
Lines that don't start with $
or >
character show the output of the previous
command.
First, make sure to have downloaded and installed Node.js. See Installing Node.js via package manager for further install information.
Now, create an empty project folder called projects
, then navigate into it.
Linux and Mac:
mkdir ~/projects
cd ~/projects
Windows CMD:
mkdir %USERPROFILE%\projects
cd %USERPROFILE%\projects
Windows PowerShell:
mkdir $env:USERPROFILE\projects
cd $env:USERPROFILE\projects
Next, create a new source file in the projects
folder and call it hello-world.js
.
Open hello-world.js
in any preferred text editor and
paste in the following content:
const http = require('node:http');
const hostname = '127.0.0.1';
const port = 3000;
const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader('Content-Type', 'text/plain');
res.end('Hello, World!\n');
});
server.listen(port, hostname, () => {
console.log(`Server running at http://${hostname}:${port}/`);
});
Save the file. Then, in the terminal window, to run the hello-world.js
file,
enter:
node hello-world.js
Output like this should appear in the terminal:
Server running at http://127.0.0.1:3000/
Now, open any preferred web browser and visit http://127.0.0.1:3000
.
If the browser displays the string Hello, World!
, that indicates
the server is working.
Assert#
Source Code: lib/assert.js
The node:assert
module provides a set of assertion functions for verifying
invariants.
Strict assertion mode#
In strict assertion mode, non-strict methods behave like their corresponding
strict methods. For example, assert.deepEqual()
will behave like
assert.deepStrictEqual()
.
In strict assertion mode, error messages for objects display a diff. In legacy assertion mode, error messages for objects display the objects, often truncated.
To use strict assertion mode:
import { strict as assert } from 'node:assert';
const assert = require('node:assert').strict;
import assert from 'node:assert/strict';
const assert = require('node:assert/strict');
Example error diff:
import { strict as assert } from 'node:assert';
assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected ... Lines skipped
//
// [
// [
// ...
// 2,
// + 3
// - '3'
// ],
// ...
// 5
// ]
const assert = require('node:assert/strict');
assert.deepEqual([[[1, 2, 3]], 4, 5], [[[1, 2, '3']], 4, 5]);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected ... Lines skipped
//
// [
// [
// ...
// 2,
// + 3
// - '3'
// ],
// ...
// 5
// ]
To deactivate the colors, use the NO_COLOR
or NODE_DISABLE_COLORS
environment variables. This will also deactivate the colors in the REPL. For
more on color support in terminal environments, read the tty
getColorDepth()
documentation.
Legacy assertion mode#
Legacy assertion mode uses the ==
operator in:
To use legacy assertion mode:
import assert from 'node:assert';
const assert = require('node:assert');
Legacy assertion mode may have surprising results, especially when using
assert.deepEqual()
:
// WARNING: This does not throw an AssertionError in legacy assertion mode!
assert.deepEqual(/a/gi, new Date());
Class: assert.AssertionError[src]#
- Extends: <errors.Error>
Indicates the failure of an assertion. All errors thrown by the node:assert
module will be instances of the AssertionError
class.
new assert.AssertionError(options)
#
options
<Object>message
<string> If provided, the error message is set to this value.actual
<any> Theactual
property on the error instance.expected
<any> Theexpected
property on the error instance.operator
<string> Theoperator
property on the error instance.stackStartFn
<Function> If provided, the generated stack trace omits frames before this function.
A subclass of Error
that indicates the failure of an assertion.
All instances contain the built-in Error
properties (message
and name
)
and:
actual
<any> Set to theactual
argument for methods such asassert.strictEqual()
.expected
<any> Set to theexpected
value for methods such asassert.strictEqual()
.generatedMessage
<boolean> Indicates if the message was auto-generated (true
) or not.code
<string> Value is alwaysERR_ASSERTION
to show that the error is an assertion error.operator
<string> Set to the passed in operator value.
import assert from 'node:assert';
// Generate an AssertionError to compare the error message later:
const { message } = new assert.AssertionError({
actual: 1,
expected: 2,
operator: 'strictEqual',
});
// Verify error output:
try {
assert.strictEqual(1, 2);
} catch (err) {
assert(err instanceof assert.AssertionError);
assert.strictEqual(err.message, message);
assert.strictEqual(err.name, 'AssertionError');
assert.strictEqual(err.actual, 1);
assert.strictEqual(err.expected, 2);
assert.strictEqual(err.code, 'ERR_ASSERTION');
assert.strictEqual(err.operator, 'strictEqual');
assert.strictEqual(err.generatedMessage, true);
}
const assert = require('node:assert');
// Generate an AssertionError to compare the error message later:
const { message } = new assert.AssertionError({
actual: 1,
expected: 2,
operator: 'strictEqual',
});
// Verify error output:
try {
assert.strictEqual(1, 2);
} catch (err) {
assert(err instanceof assert.AssertionError);
assert.strictEqual(err.message, message);
assert.strictEqual(err.name, 'AssertionError');
assert.strictEqual(err.actual, 1);
assert.strictEqual(err.expected, 2);
assert.strictEqual(err.code, 'ERR_ASSERTION');
assert.strictEqual(err.operator, 'strictEqual');
assert.strictEqual(err.generatedMessage, true);
}
Class: assert.CallTracker
#
This feature is deprecated and will be removed in a future version.
Please consider using alternatives such as the
mock
helper function.
new assert.CallTracker()
#
Creates a new CallTracker
object which can be used to track if functions
were called a specific number of times. The tracker.verify()
must be called
for the verification to take place. The usual pattern would be to call it in a
process.on('exit')
handler.
import assert from 'node:assert';
import process from 'node:process';
const tracker = new assert.CallTracker();
function func() {}
// callsfunc() must be called exactly 1 time before tracker.verify().
const callsfunc = tracker.calls(func, 1);
callsfunc();
// Calls tracker.verify() and verifies if all tracker.calls() functions have
// been called exact times.
process.on('exit', () => {
tracker.verify();
});
const assert = require('node:assert');
const tracker = new assert.CallTracker();
function func() {}
// callsfunc() must be called exactly 1 time before tracker.verify().
const callsfunc = tracker.calls(func, 1);
callsfunc();
// Calls tracker.verify() and verifies if all tracker.calls() functions have
// been called exact times.
process.on('exit', () => {
tracker.verify();
});
tracker.calls([fn][, exact])
#
fn
<Function> Default: A no-op function.exact
<number> Default:1
.- Returns: <Function> that wraps
fn
.
The wrapper function is expected to be called exactly exact
times. If the
function has not been called exactly exact
times when
tracker.verify()
is called, then tracker.verify()
will throw an
error.
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func);
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func);
tracker.getCalls(fn)
#
-
fn
<Function>. -
Returns: <Array> with all the calls to a tracked function.
-
Object <Object>
import assert from 'node:assert';
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc(1, 2, 3);
assert.deepStrictEqual(tracker.getCalls(callsfunc),
[{ thisArg: undefined, arguments: [1, 2, 3] }]);
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc(1, 2, 3);
assert.deepStrictEqual(tracker.getCalls(callsfunc),
[{ thisArg: undefined, arguments: [1, 2, 3] }]);
tracker.report()
#
- Returns: <Array> of objects containing information about the wrapper functions
returned by
tracker.calls()
. - Object <Object>
The arrays contains information about the expected and actual number of calls of the functions that have not been called the expected number of times.
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
// Returns an array containing information on callsfunc()
console.log(tracker.report());
// [
// {
// message: 'Expected the func function to be executed 2 time(s) but was
// executed 0 time(s).',
// actual: 0,
// expected: 2,
// operator: 'func',
// stack: stack trace
// }
// ]
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
// Returns an array containing information on callsfunc()
console.log(tracker.report());
// [
// {
// message: 'Expected the func function to be executed 2 time(s) but was
// executed 0 time(s).',
// actual: 0,
// expected: 2,
// operator: 'func',
// stack: stack trace
// }
// ]
tracker.reset([fn])
#
fn
<Function> a tracked function to reset.
Reset calls of the call tracker. If a tracked function is passed as an argument, the calls will be reset for it. If no arguments are passed, all tracked functions will be reset
import assert from 'node:assert';
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc();
// Tracker was called once
assert.strictEqual(tracker.getCalls(callsfunc).length, 1);
tracker.reset(callsfunc);
assert.strictEqual(tracker.getCalls(callsfunc).length, 0);
const assert = require('node:assert');
const tracker = new assert.CallTracker();
function func() {}
const callsfunc = tracker.calls(func);
callsfunc();
// Tracker was called once
assert.strictEqual(tracker.getCalls(callsfunc).length, 1);
tracker.reset(callsfunc);
assert.strictEqual(tracker.getCalls(callsfunc).length, 0);
tracker.verify()
#
Iterates through the list of functions passed to
tracker.calls()
and will throw an error for functions that
have not been called the expected number of times.
import assert from 'node:assert';
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
callsfunc();
// Will throw an error since callsfunc() was only called once.
tracker.verify();
const assert = require('node:assert');
// Creates call tracker.
const tracker = new assert.CallTracker();
function func() {}
// Returns a function that wraps func() that must be called exact times
// before tracker.verify().
const callsfunc = tracker.calls(func, 2);
callsfunc();
// Will throw an error since callsfunc() was only called once.
tracker.verify();
assert(value[, message])
#
An alias of assert.ok()
.
assert.deepEqual(actual, expected[, message])
#
Strict assertion mode
An alias of assert.deepStrictEqual()
.
Legacy assertion mode
assert.deepStrictEqual()
instead.Tests for deep equality between the actual
and expected
parameters. Consider
using assert.deepStrictEqual()
instead. assert.deepEqual()
can have
surprising results.
Deep equality means that the enumerable "own" properties of child objects are also recursively evaluated by the following rules.
Comparison details#
- Primitive values are compared with the
==
operator, with the exception ofNaN
. It is treated as being identical in case both sides areNaN
. - Type tags of objects should be the same.
- Only enumerable "own" properties are considered.
Error
names and messages are always compared, even if these are not enumerable properties.- Object wrappers are compared both as objects and unwrapped values.
Object
properties are compared unordered.Map
keys andSet
items are compared unordered.- Recursion stops when both sides differ or both sides encounter a circular reference.
- Implementation does not test the
[[Prototype]]
of objects. Symbol
properties are not compared.WeakMap
andWeakSet
comparison does not rely on their values.RegExp
lastIndex, flags, and source are always compared, even if these are not enumerable properties.
The following example does not throw an AssertionError
because the
primitives are compared using the ==
operator.
import assert from 'node:assert';
// WARNING: This does not throw an AssertionError!
assert.deepEqual('+00000000', false);
const assert = require('node:assert');
// WARNING: This does not throw an AssertionError!
assert.deepEqual('+00000000', false);
"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:
import assert from 'node:assert';
const obj1 = {
a: {
b: 1,
},
};
const obj2 = {
a: {
b: 2,
},
};
const obj3 = {
a: {
b: 1,
},
};
const obj4 = { __proto__: obj1 };
assert.deepEqual(obj1, obj1);
// OK
// Values of b are different:
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
assert.deepEqual(obj1, obj3);
// OK
// Prototypes are ignored:
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
const assert = require('node:assert');
const obj1 = {
a: {
b: 1,
},
};
const obj2 = {
a: {
b: 2,
},
};
const obj3 = {
a: {
b: 1,
},
};
const obj4 = { __proto__: obj1 };
assert.deepEqual(obj1, obj1);
// OK
// Values of b are different:
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
assert.deepEqual(obj1, obj3);
// OK
// Prototypes are ignored:
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned. If the message
parameter is an instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.deepStrictEqual(actual, expected[, message])
#
Tests for deep equality between the actual
and expected
parameters.
"Deep" equality means that the enumerable "own" properties of child objects
are recursively evaluated also by the following rules.
Comparison details#
- Primitive values are compared using
Object.is()
. - Type tags of objects should be the same.
[[Prototype]]
of objects are compared using the===
operator.- Only enumerable "own" properties are considered.
Error
names and messages are always compared, even if these are not enumerable properties.- Enumerable own
Symbol
properties are compared as well. - Object wrappers are compared both as objects and unwrapped values.
Object
properties are compared unordered.Map
keys andSet
items are compared unordered.- Recursion stops when both sides differ or both sides encounter a circular reference.
WeakMap
andWeakSet
comparison does not rely on their values. See below for further details.RegExp
lastIndex, flags, and source are always compared, even if these are not enumerable properties.
import assert from 'node:assert/strict';
// This fails because 1 !== '1'.
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// {
// + a: 1
// - a: '1'
// }
// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
// Different [[Prototype]]:
assert.deepStrictEqual(object, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + {}
// - Date {}
// Different type tags:
assert.deepStrictEqual(date, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 2018-04-26T00:49:08.604Z
// - Date {}
assert.deepStrictEqual(NaN, NaN);
// OK because Object.is(NaN, NaN) is true.
// Different unwrapped numbers:
assert.deepStrictEqual(new Number(1), new Number(2));
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + [Number: 1]
// - [Number: 2]
assert.deepStrictEqual(new String('foo'), Object('foo'));
// OK because the object and the string are identical when unwrapped.
assert.deepStrictEqual(-0, -0);
// OK
// Different zeros:
assert.deepStrictEqual(0, -0);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 0
// - -0
const symbol1 = Symbol();
const symbol2 = Symbol();
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
// OK, because it is the same symbol on both objects.
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
//
// {
// [Symbol()]: 1
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
const assert = require('node:assert/strict');
// This fails because 1 !== '1'.
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// {
// + a: 1
// - a: '1'
// }
// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
// Different [[Prototype]]:
assert.deepStrictEqual(object, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + {}
// - Date {}
// Different type tags:
assert.deepStrictEqual(date, fakeDate);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 2018-04-26T00:49:08.604Z
// - Date {}
assert.deepStrictEqual(NaN, NaN);
// OK because Object.is(NaN, NaN) is true.
// Different unwrapped numbers:
assert.deepStrictEqual(new Number(1), new Number(2));
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + [Number: 1]
// - [Number: 2]
assert.deepStrictEqual(new String('foo'), Object('foo'));
// OK because the object and the string are identical when unwrapped.
assert.deepStrictEqual(-0, -0);
// OK
// Different zeros:
assert.deepStrictEqual(0, -0);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// + 0
// - -0
const symbol1 = Symbol();
const symbol2 = Symbol();
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol1]: 1 });
// OK, because it is the same symbol on both objects.
assert.deepStrictEqual({ [symbol1]: 1 }, { [symbol2]: 1 });
// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:
//
// {
// [Symbol()]: 1
// }
const weakMap1 = new WeakMap();
const weakMap2 = new WeakMap([[{}, {}]]);
const weakMap3 = new WeakMap();
weakMap3.unequal = true;
assert.deepStrictEqual(weakMap1, weakMap2);
// OK, because it is impossible to compare the entries
// Fails because weakMap3 has a property that weakMap1 does not contain:
assert.deepStrictEqual(weakMap1, weakMap3);
// AssertionError: Expected inputs to be strictly deep-equal:
// + actual - expected
//
// WeakMap {
// + [items unknown]
// - [items unknown],
// - unequal: true
// }
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned. If the message
parameter is an instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.doesNotMatch(string, regexp[, message])
#
Expects the string
input not to match the regular expression.
import assert from 'node:assert/strict';
assert.doesNotMatch('I will fail', /fail/);
// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...
assert.doesNotMatch(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.doesNotMatch('I will pass', /different/);
// OK
const assert = require('node:assert/strict');
assert.doesNotMatch('I will fail', /fail/);
// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...
assert.doesNotMatch(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.doesNotMatch('I will pass', /different/);
// OK
If the values do match, or if the string
argument is of another type than
string
, an AssertionError
is thrown with a message
property set equal
to the value of the message
parameter. If the message
parameter is
undefined, a default error message is assigned. If the message
parameter is an
instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.doesNotReject(asyncFn[, error][, message])
#
asyncFn
<Function> | <Promise>error
<RegExp> | <Function>message
<string>
Awaits the asyncFn
promise or, if asyncFn
is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is not rejected.
If asyncFn
is a function and it throws an error synchronously,
assert.doesNotReject()
will return a rejected Promise
with that error. If
the function does not return a promise, assert.doesNotReject()
will return a
rejected Promise
with an ERR_INVALID_RETURN_VALUE
error. In both cases
the error handler is skipped.
Using assert.doesNotReject()
is actually not useful because there is little
benefit in catching a rejection and then rejecting it again. Instead, consider
adding a comment next to the specific code path that should not reject and keep
error messages as expressive as possible.
If specified, error
can be a Class
, RegExp
, or a validation
function. See assert.throws()
for more details.
Besides the async nature to await the completion behaves identically to
assert.doesNotThrow()
.
import assert from 'node:assert/strict';
await assert.doesNotReject(
async () => {
throw new TypeError('Wrong value');
},
SyntaxError,
);
const assert = require('node:assert/strict');
(async () => {
await assert.doesNotReject(
async () => {
throw new TypeError('Wrong value');
},
SyntaxError,
);
})();
import assert from 'node:assert/strict';
assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))
.then(() => {
// ...
});
const assert = require('node:assert/strict');
assert.doesNotReject(Promise.reject(new TypeError('Wrong value')))
.then(() => {
// ...
});
assert.doesNotThrow(fn[, error][, message])
#
fn
<Function>error
<RegExp> | <Function>message
<string>
Asserts that the function fn
does not throw an error.
Using assert.doesNotThrow()
is actually not useful because there
is no benefit in catching an error and then rethrowing it. Instead, consider
adding a comment next to the specific code path that should not throw and keep
error messages as expressive as possible.
When assert.doesNotThrow()
is called, it will immediately call the fn
function.
If an error is thrown and it is the same type as that specified by the error
parameter, then an AssertionError
is thrown. If the error is of a
different type, or if the error
parameter is undefined, the error is
propagated back to the caller.
If specified, error
can be a Class
, RegExp
, or a validation
function. See assert.throws()
for more details.
The following, for instance, will throw the TypeError
because there is no
matching error type in the assertion:
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError,
);
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError,
);
However, the following will result in an AssertionError
with the message
'Got unwanted exception...':
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
);
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
);
If an AssertionError
is thrown and a value is provided for the message
parameter, the value of message
will be appended to the AssertionError
message:
import assert from 'node:assert/strict';
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
/Wrong value/,
'Whoops',
);
// Throws: AssertionError: Got unwanted exception: Whoops
const assert = require('node:assert/strict');
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
/Wrong value/,
'Whoops',
);
// Throws: AssertionError: Got unwanted exception: Whoops
assert.equal(actual, expected[, message])
#
Strict assertion mode
An alias of assert.strictEqual()
.
Legacy assertion mode
assert.strictEqual()
instead.Tests shallow, coercive equality between the actual
and expected
parameters
using the ==
operator. NaN
is specially handled
and treated as being identical if both sides are NaN
.
import assert from 'node:assert';
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(NaN, NaN);
// OK
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
const assert = require('node:assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(NaN, NaN);
// OK
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned. If the message
parameter is an instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.fail([message])
#
Throws an AssertionError
with the provided error message or a default
error message. If the message
parameter is an instance of an Error
then
it will be thrown instead of the AssertionError
.
import assert from 'node:assert/strict';
assert.fail();
// AssertionError [ERR_ASSERTION]: Failed
assert.fail('boom');
// AssertionError [ERR_ASSERTION]: boom
assert.fail(new TypeError('need array'));
// TypeError: need array
const assert = require('node:assert/strict');
assert.fail();
// AssertionError [ERR_ASSERTION]: Failed
assert.fail('boom');
// AssertionError [ERR_ASSERTION]: boom
assert.fail(new TypeError('need array'));
// TypeError: need array
Using assert.fail()
with more than two arguments is possible but deprecated.
See below for further details.
assert.fail(actual, expected[, message[, operator[, stackStartFn]]])
#
assert.fail([message])
or other assert
functions instead.actual
<any>expected
<any>message
<string> | <Error>operator
<string> Default:'!='
stackStartFn
<Function> Default:assert.fail
If message
is falsy, the error message is set as the values of actual
and
expected
separated by the provided operator
. If just the two actual
and
expected
arguments are provided, operator
will default to '!='
. If
message
is provided as third argument it will be used as the error message and
the other arguments will be stored as properties on the thrown object. If
stackStartFn
is provided, all stack frames above that function will be
removed from stacktrace (see Error.captureStackTrace
). If no arguments are
given, the default message Failed
will be used.
import assert from 'node:assert/strict';
assert.fail('a', 'b');
// AssertionError [ERR_ASSERTION]: 'a' != 'b'
assert.fail(1, 2, undefined, '>');
// AssertionError [ERR_ASSERTION]: 1 > 2
assert.fail(1, 2, 'fail');
// AssertionError [ERR_ASSERTION]: fail
assert.fail(1, 2, 'whoops', '>');
// AssertionError [ERR_ASSERTION]: whoops
assert.fail(1, 2, new TypeError('need array'));
// TypeError: need array
const assert = require('node:assert/strict');
assert.fail('a', 'b');
// AssertionError [ERR_ASSERTION]: 'a' != 'b'
assert.fail(1, 2, undefined, '>');
// AssertionError [ERR_ASSERTION]: 1 > 2
assert.fail(1, 2, 'fail');
// AssertionError [ERR_ASSERTION]: fail
assert.fail(1, 2, 'whoops', '>');
// AssertionError [ERR_ASSERTION]: whoops
assert.fail(1, 2, new TypeError('need array'));
// TypeError: need array
In the last three cases actual
, expected
, and operator
have no
influence on the error message.
Example use of stackStartFn
for truncating the exception's stacktrace:
import assert from 'node:assert/strict';
function suppressFrame() {
assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError [ERR_ASSERTION]: 'a' !== 'b'
// at repl:1:1
// at ContextifyScript.Script.runInThisContext (vm.js:44:33)
// ...
const assert = require('node:assert/strict');
function suppressFrame() {
assert.fail('a', 'b', undefined, '!==', suppressFrame);
}
suppressFrame();
// AssertionError [ERR_ASSERTION]: 'a' !== 'b'
// at repl:1:1
// at ContextifyScript.Script.runInThisContext (vm.js:44:33)
// ...
assert.ifError(value)
#
value
<any>
Throws value
if value
is not undefined
or null
. This is useful when
testing the error
argument in callbacks. The stack trace contains all frames
from the error passed to ifError()
including the potential new frames for
ifError()
itself.
import assert from 'node:assert/strict';
assert.ifError(null);
// OK
assert.ifError(0);
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0
assert.ifError('error');
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'
assert.ifError(new Error());
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error
// Create some random error frames.
let err;
(function errorFrame() {
err = new Error('test error');
})();
(function ifErrorFrame() {
assert.ifError(err);
})();
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error
// at ifErrorFrame
// at errorFrame
const assert = require('node:assert/strict');
assert.ifError(null);
// OK
assert.ifError(0);
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0
assert.ifError('error');
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'
assert.ifError(new Error());
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error
// Create some random error frames.
let err;
(function errorFrame() {
err = new Error('test error');
})();
(function ifErrorFrame() {
assert.ifError(err);
})();
// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error
// at ifErrorFrame
// at errorFrame
assert.match(string, regexp[, message])
#
Expects the string
input to match the regular expression.
import assert from 'node:assert/strict';
assert.match('I will fail', /pass/);
// AssertionError [ERR_ASSERTION]: The input did not match the regular ...
assert.match(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.match('I will pass', /pass/);
// OK
const assert = require('node:assert/strict');
assert.match('I will fail', /pass/);
// AssertionError [ERR_ASSERTION]: The input did not match the regular ...
assert.match(123, /pass/);
// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.
assert.match('I will pass', /pass/);
// OK
If the values do not match, or if the string
argument is of another type than
string
, an AssertionError
is thrown with a message
property set equal
to the value of the message
parameter. If the message
parameter is
undefined, a default error message is assigned. If the message
parameter is an
instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.notDeepEqual(actual, expected[, message])
#
Strict assertion mode
An alias of assert.notDeepStrictEqual()
.
Legacy assertion mode
assert.notDeepStrictEqual()
instead.Tests for any deep inequality. Opposite of assert.deepEqual()
.
import assert from 'node:assert';
const obj1 = {
a: {
b: 1,
},
};
const obj2 = {
a: {
b: 2,
},
};
const obj3 = {
a: {
b: 1,
},
};
const obj4 = { __proto__: obj1 };
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK
const assert = require('node:assert');
const obj1 = {
a: {
b: 1,
},
};
const obj2 = {
a: {
b: 2,
},
};
const obj3 = {
a: {
b: 1,
},
};
const obj4 = { __proto__: obj1 };
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK
If the values are deeply equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned. If the
message
parameter is an instance of an Error
then it will be thrown
instead of the AssertionError
.
assert.notDeepStrictEqual(actual, expected[, message])
#
Tests for deep strict inequality. Opposite of assert.deepStrictEqual()
.
import assert from 'node:assert/strict';
assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
const assert = require('node:assert/strict');
assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
If the values are deeply and strictly equal, an AssertionError
is thrown
with a message
property set equal to the value of the message
parameter. If
the message
parameter is undefined, a default error message is assigned. If
the message
parameter is an instance of an Error
then it will be thrown
instead of the AssertionError
.
assert.notEqual(actual, expected[, message])
#
Strict assertion mode
An alias of assert.notStrictEqual()
.
Legacy assertion mode
assert.notStrictEqual()
instead.Tests shallow, coercive inequality with the !=
operator. NaN
is
specially handled and treated as being identical if both sides are NaN
.
import assert from 'node:assert';
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
const assert = require('node:assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
If the values are equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned. If the message
parameter is an instance of an Error
then it will be thrown instead of the
AssertionError
.
assert.notStrictEqual(actual, expected[, message])
#
Tests strict inequality between the actual
and expected
parameters as
determined by Object.is()
.
import assert from 'node:assert/strict';
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
//
// 1
assert.notStrictEqual(1, '1');
// OK
const assert = require('node:assert/strict');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:
//
// 1
assert.notStrictEqual(1, '1');
// OK
If the values are strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned. If the
message
parameter is an instance of an Error
then it will be thrown
instead of the AssertionError
.
assert.ok(value[, message])
#
Tests if value
is truthy. It is equivalent to
assert.equal(!!value, true, message)
.
If value
is not truthy, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined
, a default error message is assigned. If the message
parameter is an instance of an Error
then it will be thrown instead of the
AssertionError
.
If no arguments are passed in at all message
will be set to the string:
'No value argument passed to `assert.ok()`'
.
Be aware that in the repl
the error message will be different to the one
thrown in a file! See below for further details.
import assert from 'node:assert/strict';
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok();
// AssertionError: No value argument passed to `assert.ok()`
assert.ok(false, 'it\'s false');
// AssertionError: it's false
// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true
// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(typeof 123 === 'string')
assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(false)
assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(0)
const assert = require('node:assert/strict');
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok();
// AssertionError: No value argument passed to `assert.ok()`
assert.ok(false, 'it\'s false');
// AssertionError: it's false
// In the repl:
assert.ok(typeof 123 === 'string');
// AssertionError: false == true
// In a file (e.g. test.js):
assert.ok(typeof 123 === 'string');
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(typeof 123 === 'string')
assert.ok(false);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(false)
assert.ok(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert.ok(0)
import assert from 'node:assert/strict';
// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert(0)
const assert = require('node:assert');
// Using `assert()` works the same:
assert(0);
// AssertionError: The expression evaluated to a falsy value:
//
// assert(0)
assert.rejects(asyncFn[, error][, message])
#
asyncFn
<Function> | <Promise>error
<RegExp> | <Function> | <Object> | <Error>message
<string>
Awaits the asyncFn
promise or, if asyncFn
is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is rejected.
If asyncFn
is a function and it throws an error synchronously,
assert.rejects()
will return a rejected Promise
with that error. If the
function does not return a promise, assert.rejects()
will return a rejected
Promise
with an ERR_INVALID_RETURN_VALUE
error. In both cases the error
handler is skipped.
Besides the async nature to await the completion behaves identically to
assert.throws()
.
If specified, error
can be a Class
, RegExp
, a validation function,
an object where each property will be tested for, or an instance of error where
each property will be tested for including the non-enumerable message
and
name
properties.
If specified, message
will be the message provided by the AssertionError
if the asyncFn
fails to reject.
import assert from 'node:assert/strict';
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
{
name: 'TypeError',
message: 'Wrong value',
},
);
const assert = require('node:assert/strict');
(async () => {
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
{
name: 'TypeError',
message: 'Wrong value',
},
);
})();
import assert from 'node:assert/strict';
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
(err) => {
assert.strictEqual(err.name, 'TypeError');
assert.strictEqual(err.message, 'Wrong value');
return true;
},
);
const assert = require('node:assert/strict');
(async () => {
await assert.rejects(
async () => {
throw new TypeError('Wrong value');
},
(err) => {
assert.strictEqual(err.name, 'TypeError');
assert.strictEqual(err.message, 'Wrong value');
return true;
},
);
})();
import assert from 'node:assert/strict';
assert.rejects(
Promise.reject(new Error('Wrong value')),
Error,
).then(() => {
// ...
});
const assert = require('node:assert/strict');
assert.rejects(
Promise.reject(new Error('Wrong value')),
Error,
).then(() => {
// ...
});
error
cannot be a string. If a string is provided as the second
argument, then error
is assumed to be omitted and the string will be used for
message
instead. This can lead to easy-to-miss mistakes. Please read the
example in assert.throws()
carefully if using a string as the second
argument gets considered.
assert.strictEqual(actual, expected[, message])
#
Tests strict equality between the actual
and expected
parameters as
determined by Object.is()
.
import assert from 'node:assert/strict';
assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
// ^
const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2
assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
const assert = require('node:assert/strict');
assert.strictEqual(1, 2);
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
//
// 1 !== 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual('Hello foobar', 'Hello World!');
// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:
// + actual - expected
//
// + 'Hello foobar'
// - 'Hello World!'
// ^
const apples = 1;
const oranges = 2;
assert.strictEqual(apples, oranges, `apples ${apples} !== oranges ${oranges}`);
// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2
assert.strictEqual(1, '1', new TypeError('Inputs are not identical'));
// TypeError: Inputs are not identical
If the values are not strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned. If the
message
parameter is an instance of an Error
then it will be thrown
instead of the AssertionError
.
assert.throws(fn[, error][, message])
#
fn
<Function>error
<RegExp> | <Function> | <Object> | <Error>message
<string>
Expects the function fn
to throw an error.
If specified, error
can be a Class
, RegExp
, a validation function,
a validation object where each property will be tested for strict deep equality,
or an instance of error where each property will be tested for strict deep
equality including the non-enumerable message
and name
properties. When
using an object, it is also possible to use a regular expression, when
validating against a string property. See below for examples.
If specified, message
will be appended to the message provided by the
AssertionError
if the fn
call fails to throw or in case the error validation
fails.
Custom validation object/error instance:
import assert from 'node:assert/strict';
const err = new TypeError('Wrong value');
err.code = 404;
err.foo = 'bar';
err.info = {
nested: true,
baz: 'text',
};
err.reg = /abc/i;
assert.throws(
() => {
throw err;
},
{
name: 'TypeError',
message: 'Wrong value',
info: {
nested: true,
baz: 'text',
},
// Only properties on the validation object will be tested for.
// Using nested objects requires all properties to be present. Otherwise
// the validation is going to fail.
},
);
// Using regular expressions to validate error properties:
assert.throws(
() => {
throw err;
},
{
// The `name` and `message` properties are strings and using regular
// expressions on those will match against the string. If they fail, an
// error is thrown.
name: /^TypeError$/,
message: /Wrong/,
foo: 'bar',
info: {
nested: true,
// It is not possible to use regular expressions for nested properties!
baz: 'text',
},
// The `reg` property contains a regular expression and only if the
// validation object contains an identical regular expression, it is going
// to pass.
reg: /abc/i,
},
);
// Fails due to the different `message` and `name` properties:
assert.throws(
() => {
const otherErr = new Error('Not found');
// Copy all enumerable properties from `err` to `otherErr`.
for (const [key, value] of Object.entries(err)) {
otherErr[key] = value;
}
throw otherErr;
},
// The error's `message` and `name` properties will also be checked when using
// an error as validation object.
err,
);
const assert = require('node:assert/strict');
const err = new TypeError('Wrong value');
err.code = 404;
err.foo = 'bar';
err.info = {
nested: true,
baz: 'text',
};
err.reg = /abc/i;
assert.throws(
() => {
throw err;
},
{
name: 'TypeError',
message: 'Wrong value',
info: {
nested: true,
baz: 'text',
},
// Only properties on the validation object will be tested for.
// Using nested objects requires all properties to be present. Otherwise
// the validation is going to fail.
},
);
// Using regular expressions to validate error properties:
assert.throws(
() => {
throw err;
},
{
// The `name` and `message` properties are strings and using regular
// expressions on those will match against the string. If they fail, an
// error is thrown.
name: /^TypeError$/,
message: /Wrong/,
foo: 'bar',
info: {
nested: true,
// It is not possible to use regular expressions for nested properties!
baz: 'text',
},
// The `reg` property contains a regular expression and only if the
// validation object contains an identical regular expression, it is going
// to pass.
reg: /abc/i,
},
);
// Fails due to the different `message` and `name` properties:
assert.throws(
() => {
const otherErr = new Error('Not found');
// Copy all enumerable properties from `err` to `otherErr`.
for (const [key, value] of Object.entries(err)) {
otherErr[key] = value;
}
throw otherErr;
},
// The error's `message` and `name` properties will also be checked when using
// an error as validation object.
err,
);
Validate instanceof using constructor:
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
Error,
);
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
Error,
);
Validate error message using RegExp
:
Using a regular expression runs .toString
on the error object, and will
therefore also include the error name.
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
/^Error: Wrong value$/,
);
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
/^Error: Wrong value$/,
);
Custom error validation:
The function must return true
to indicate all internal validations passed.
It will otherwise fail with an AssertionError
.
import assert from 'node:assert/strict';
assert.throws(
() => {
throw new Error('Wrong value');
},
(err) => {
assert(err instanceof Error);
assert(/value/.test(err));
// Avoid returning anything from validation functions besides `true`.
// Otherwise, it's not clear what part of the validation failed. Instead,
// throw an error about the specific validation that failed (as done in this
// example) and add as much helpful debugging information to that error as
// possible.
return true;
},
'unexpected error',
);
const assert = require('node:assert/strict');
assert.throws(
() => {
throw new Error('Wrong value');
},
(err) => {
assert(err instanceof Error);
assert(/value/.test(err));
// Avoid returning anything from validation functions besides `true`.
// Otherwise, it's not clear what part of the validation failed. Instead,
// throw an error about the specific validation that failed (as done in this
// example) and add as much helpful debugging information to that error as
// possible.
return true;
},
'unexpected error',
);
error
cannot be a string. If a string is provided as the second
argument, then error
is assumed to be omitted and the string will be used for
message
instead. This can lead to easy-to-miss mistakes. Using the same
message as the thrown error message is going to result in an
ERR_AMBIGUOUS_ARGUMENT
error. Please read the example below carefully if using
a string as the second argument gets considered:
import assert from 'node:assert/strict';
function throwingFirst() {
throw new Error('First');
}
function throwingSecond() {
throw new Error('Second');
}
function notThrowing() {}
// The second argument is a string and the input function threw an Error.
// The first case will not throw as it does not match for the error message
// thrown by the input function!
assert.throws(throwingFirst, 'Second');
// In the next example the message has no benefit over the message from the
// error and since it is not clear if the user intended to actually match
// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
assert.throws(throwingSecond, 'Second');
// TypeError [ERR_AMBIGUOUS_ARGUMENT]
// The string is only used (as message) in case the function does not throw:
assert.throws(notThrowing, 'Second');
// AssertionError [ERR_ASSERTION]: Missing expected exception: Second
// If it was intended to match for the error message do this instead:
// It does not throw because the error messages match.
assert.throws(throwingSecond, /Second$/);
// If the error message does not match, an AssertionError is thrown.
assert.throws(throwingFirst, /Second$/);
// AssertionError [ERR_ASSERTION]
const assert = require('node:assert/strict');
function throwingFirst() {
throw new Error('First');
}
function throwingSecond() {
throw new Error('Second');
}
function notThrowing() {}
// The second argument is a string and the input function threw an Error.
// The first case will not throw as it does not match for the error message
// thrown by the input function!
assert.throws(throwingFirst, 'Second');
// In the next example the message has no benefit over the message from the
// error and since it is not clear if the user intended to actually match
// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.
assert.throws(throwingSecond, 'Second');
// TypeError [ERR_AMBIGUOUS_ARGUMENT]
// The string is only used (as message) in case the function does not throw:
assert.throws(notThrowing, 'Second');
// AssertionError [ERR_ASSERTION]: Missing expected exception: Second
// If it was intended to match for the error message do this instead:
// It does not throw because the error messages match.
assert.throws(throwingSecond, /Second$/);
// If the error message does not match, an AssertionError is thrown.
assert.throws(throwingFirst, /Second$/);
// AssertionError [ERR_ASSERTION]
Due to the confusing error-prone notation, avoid a string as the second argument.
Asynchronous context tracking#
Source Code: lib/async_hooks.js
Introduction#
These classes are used to associate state and propagate it throughout callbacks and promise chains. They allow storing data throughout the lifetime of a web request or any other asynchronous duration. It is similar to thread-local storage in other languages.
The AsyncLocalStorage
and AsyncResource
classes are part of the
node:async_hooks
module:
import { AsyncLocalStorage, AsyncResource } from 'node:async_hooks';
const { AsyncLocalStorage, AsyncResource } = require('node:async_hooks');
Class: AsyncLocalStorage
#
This class creates stores that stay coherent through asynchronous operations.
While you can create your own implementation on top of the node:async_hooks
module, AsyncLocalStorage
should be preferred as it is a performant and memory
safe implementation that involves significant optimizations that are non-obvious
to implement.
The following example uses AsyncLocalStorage
to build a simple logger
that assigns IDs to incoming HTTP requests and includes them in messages
logged within each request.
import http from 'node:http';
import { AsyncLocalStorage } from 'node:async_hooks';
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('http://localhost:8080');
http.get('http://localhost:8080');
// Prints:
// 0: start
// 1: start
// 0: finish
// 1: finish
const http = require('node:http');
const { AsyncLocalStorage } = require('node:async_hooks');
const asyncLocalStorage = new AsyncLocalStorage();
function logWithId(msg) {
const id = asyncLocalStorage.getStore();
console.log(`${id !== undefined ? id : '-'}:`, msg);
}
let idSeq = 0;
http.createServer((req, res) => {
asyncLocalStorage.run(idSeq++, () => {
logWithId('start');
// Imagine any chain of async operations here
setImmediate(() => {
logWithId('finish');
res.end();
});
});
}).listen(8080);
http.get('http://localhost:8080');
http.get('http://localhost:8080');
// Prints:
// 0: start
// 1: start
// 0: finish
// 1: finish
Each instance of AsyncLocalStorage
maintains an independent storage context.
Multiple instances can safely exist simultaneously without risk of interfering
with each other's data.
new AsyncLocalStorage()
#
Creates a new instance of AsyncLocalStorage
. Store is only provided within a
run()
call or after an enterWith()
call.
Static method: AsyncLocalStorage.bind(fn)
#
fn
<Function> The function to bind to the current execution context.- Returns: <Function> A new function that calls
fn
within the captured execution context.
Binds the given function to the current execution context.
Static method: AsyncLocalStorage.snapshot()
#
- Returns: <Function> A new function with the signature
(fn: (...args) : R, ...args) : R
.
Captures the current execution context and returns a function that accepts a function as an argument. Whenever the returned function is called, it calls the function passed to it within the captured context.
const asyncLocalStorage = new AsyncLocalStorage();
const runInAsyncScope = asyncLocalStorage.run(123, () => AsyncLocalStorage.snapshot());
const result = asyncLocalStorage.run(321, () => runInAsyncScope(() => asyncLocalStorage.getStore()));
console.log(result); // returns 123
AsyncLocalStorage.snapshot() can replace the use of AsyncResource for simple async context tracking purposes, for example:
class Foo {
#runInAsyncScope = AsyncLocalStorage.snapshot();
get() { return this.#runInAsyncScope(() => asyncLocalStorage.getStore()); }
}
const foo = asyncLocalStorage.run(123, () => new Foo());
console.log(asyncLocalStorage.run(321, () => foo.get())); // returns 123
asyncLocalStorage.disable()
#
Disables the instance of AsyncLocalStorage
. All subsequent calls
to asyncLocalStorage.getStore()
will return undefined
until
asyncLocalStorage.run()
or asyncLocalStorage.enterWith()
is called again.
When calling asyncLocalStorage.disable()
, all current contexts linked to the
instance will be exited.
Calling asyncLocalStorage.disable()
is required before the
asyncLocalStorage
can be garbage collected. This does not apply to stores
provided by the asyncLocalStorage
, as those objects are garbage collected
along with the corresponding async resources.
Use this method when the asyncLocalStorage
is not in use anymore
in the current process.
asyncLocalStorage.getStore()
#
- Returns: <any>
Returns the current store.
If called outside of an asynchronous context initialized by
calling asyncLocalStorage.run()
or asyncLocalStorage.enterWith()
, it
returns undefined
.
asyncLocalStorage.enterWith(store)
#
store
<any>
Transitions into the context for the remainder of the current synchronous execution and then persists the store through any following asynchronous calls.
Example:
const store = { id: 1 };
// Replaces previous store with the given store object
asyncLocalStorage.enterWith(store);
asyncLocalStorage.getStore(); // Returns the store object
someAsyncOperation(() => {
asyncLocalStorage.getStore(); // Returns the same object
});
This transition will continue for the entire synchronous execution.
This means that if, for example, the context is entered within an event
handler subsequent event handlers will also run within that context unless
specifically bound to another context with an AsyncResource
. That is why
run()
should be preferred over enterWith()
unless there are strong reasons
to use the latter method.
const store = { id: 1 };
emitter.on('my-event', () => {
asyncLocalStorage.enterWith(store);
});
emitter.on('my-event', () => {
asyncLocalStorage.getStore(); // Returns the same object
});
asyncLocalStorage.getStore(); // Returns undefined
emitter.emit('my-event');
asyncLocalStorage.getStore(); // Returns the same object
asyncLocalStorage.run(store, callback[, ...args])
#
store
<any>callback
<Function>...args
<any>
Runs a function synchronously within a context and returns its return value. The store is not accessible outside of the callback function. The store is accessible to any asynchronous operations created within the callback.
The optional args
are passed to the callback function.
If the callback function throws an error, the error is thrown by run()
too.
The stacktrace is not impacted by this call and the context is exited.
Example:
const store = { id: 2 };
try {
asyncLocalStorage.run(store, () => {
asyncLocalStorage.getStore(); // Returns the store object
setTimeout(() => {
asyncLocalStorage.getStore(); // Returns the store object
}, 200);
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns undefined
// The error will be caught here
}
asyncLocalStorage.exit(callback[, ...args])
#
callback
<Function>...args
<any>
Runs a function synchronously outside of a context and returns its
return value. The store is not accessible within the callback function or
the asynchronous operations created within the callback. Any getStore()
call done within the callback function will always return undefined
.
The optional args
are passed to the callback function.
If the callback function throws an error, the error is thrown by exit()
too.
The stacktrace is not impacted by this call and the context is re-entered.
Example:
// Within a call to run
try {
asyncLocalStorage.getStore(); // Returns the store object or value
asyncLocalStorage.exit(() => {
asyncLocalStorage.getStore(); // Returns undefined
throw new Error();
});
} catch (e) {
asyncLocalStorage.getStore(); // Returns the same object or value
// The error will be caught here
}
Usage with async/await
#
If, within an async function, only one await
call is to run within a context,
the following pattern should be used:
async function fn() {
await asyncLocalStorage.run(new Map(), () => {
asyncLocalStorage.getStore().set('key', value);
return foo(); // The return value of foo will be awaited
});
}
In this example, the store is only available in the callback function and the
functions called by foo
. Outside of run
, calling getStore
will return
undefined
.
Troubleshooting: Context loss#
In most cases, AsyncLocalStorage
works without issues. In rare situations, the
current store is lost in one of the asynchronous operations.
If your code is callback-based, it is enough to promisify it with
util.promisify()
so it starts working with native promises.
If you need to use a callback-based API or your code assumes
a custom thenable implementation, use the AsyncResource
class
to associate the asynchronous operation with the correct execution context.
Find the function call responsible for the context loss by logging the content
of asyncLocalStorage.getStore()
after the calls you suspect are responsible
for the loss. When the code logs undefined
, the last callback called is
probably responsible for the context loss.
Class: AsyncResource
#
The class AsyncResource
is designed to be extended by the embedder's async
resources. Using this, users can easily trigger the lifetime events of their
own resources.
The init
hook will trigger when an AsyncResource
is instantiated.
The following is an overview of the AsyncResource
API.
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false },
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(
type, { triggerAsyncId: executionAsyncId(), requireManualDestroy: false },
);
// Run a function in the execution context of the resource. This will
// * establish the context of the resource
// * trigger the AsyncHooks before callbacks
// * call the provided function `fn` with the supplied arguments
// * trigger the AsyncHooks after callbacks
// * restore the original execution context
asyncResource.runInAsyncScope(fn, thisArg, ...args);
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
new AsyncResource(type[, options])
#
type
<string> The type of async event.options
<Object>triggerAsyncId
<number> The ID of the execution context that created this async event. Default:executionAsyncId()
.requireManualDestroy
<boolean> If set totrue
, disablesemitDestroy
when the object is garbage collected. This usually does not need to be set (even ifemitDestroy
is called manually), unless the resource'sasyncId
is retrieved and the sensitive API'semitDestroy
is called with it. When set tofalse
, theemitDestroy
call on garbage collection will only take place if there is at least one activedestroy
hook. Default:false
.
Example usage:
class DBQuery extends AsyncResource {
constructor(db) {
super('DBQuery');
this.db = db;
}
getInfo(query, callback) {
this.db.get(query, (err, data) => {
this.runInAsyncScope(callback, null, err, data);
});
}
close() {
this.db = null;
this.emitDestroy();
}
}
Static method: AsyncResource.bind(fn[, type[, thisArg]])
#
fn
<Function> The function to bind to the current execution context.type
<string> An optional name to associate with the underlyingAsyncResource
.thisArg
<any>
Binds the given function to the current execution context.
asyncResource.bind(fn[, thisArg])
#
fn
<Function> The function to bind to the currentAsyncResource
.thisArg
<any>
Binds the given function to execute to this AsyncResource
's scope.
asyncResource.runInAsyncScope(fn[, thisArg, ...args])
#
fn
<Function> The function to call in the execution context of this async resource.thisArg
<any> The receiver to be used for the function call....args
<any> Optional arguments to pass to the function.
Call the provided function with the provided arguments in the execution context of the async resource. This will establish the context, trigger the AsyncHooks before callbacks, call the function, trigger the AsyncHooks after callbacks, and then restore the original execution context.
asyncResource.emitDestroy()
#
- Returns: <AsyncResource> A reference to
asyncResource
.
Call all destroy
hooks. This should only ever be called once. An error will
be thrown if it is called more than once. This must be manually called. If
the resource is left to be collected by the GC then the destroy
hooks will
never be called.
asyncResource.asyncId()
#
- Returns: <number> The unique
asyncId
assigned to the resource.
asyncResource.triggerAsyncId()
#
- Returns: <number> The same
triggerAsyncId
that is passed to theAsyncResource
constructor.
Using AsyncResource
for a Worker
thread pool#
The following example shows how to use the AsyncResource
class to properly
provide async tracking for a Worker
pool. Other resource pools, such as
database connection pools, can follow a similar model.
Assuming that the task is adding two numbers, using a file named
task_processor.js
with the following content:
import { parentPort } from 'node:worker_threads';
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
const { parentPort } = require('node:worker_threads');
parentPort.on('message', (task) => {
parentPort.postMessage(task.a + task.b);
});
a Worker pool around it could use the following structure:
import { AsyncResource } from 'node:async_hooks';
import { EventEmitter } from 'node:events';
import path from 'node:path';
import { Worker } from 'node:worker_threads';
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
export default class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(new URL('task_processor.js', import.meta.url));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
const { AsyncResource } = require('node:async_hooks');
const { EventEmitter } = require('node:events');
const path = require('node:path');
const { Worker } = require('node:worker_threads');
const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');
class WorkerPoolTaskInfo extends AsyncResource {
constructor(callback) {
super('WorkerPoolTaskInfo');
this.callback = callback;
}
done(err, result) {
this.runInAsyncScope(this.callback, null, err, result);
this.emitDestroy(); // `TaskInfo`s are used only once.
}
}
class WorkerPool extends EventEmitter {
constructor(numThreads) {
super();
this.numThreads = numThreads;
this.workers = [];
this.freeWorkers = [];
this.tasks = [];
for (let i = 0; i < numThreads; i++)
this.addNewWorker();
// Any time the kWorkerFreedEvent is emitted, dispatch
// the next task pending in the queue, if any.
this.on(kWorkerFreedEvent, () => {
if (this.tasks.length > 0) {
const { task, callback } = this.tasks.shift();
this.runTask(task, callback);
}
});
}
addNewWorker() {
const worker = new Worker(path.resolve(__dirname, 'task_processor.js'));
worker.on('message', (result) => {
// In case of success: Call the callback that was passed to `runTask`,
// remove the `TaskInfo` associated with the Worker, and mark it as free
// again.
worker[kTaskInfo].done(null, result);
worker[kTaskInfo] = null;
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
});
worker.on('error', (err) => {
// In case of an uncaught exception: Call the callback that was passed to
// `runTask` with the error.
if (worker[kTaskInfo])
worker[kTaskInfo].done(err, null);
else
this.emit('error', err);
// Remove the worker from the list and start a new Worker to replace the
// current one.
this.workers.splice(this.workers.indexOf(worker), 1);
this.addNewWorker();
});
this.workers.push(worker);
this.freeWorkers.push(worker);
this.emit(kWorkerFreedEvent);
}
runTask(task, callback) {
if (this.freeWorkers.length === 0) {
// No free threads, wait until a worker thread becomes free.
this.tasks.push({ task, callback });
return;
}
const worker = this.freeWorkers.pop();
worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
worker.postMessage(task);
}
close() {
for (const worker of this.workers) worker.terminate();
}
}
module.exports = WorkerPool;
Without the explicit tracking added by the WorkerPoolTaskInfo
objects,
it would appear that the callbacks are associated with the individual Worker
objects. However, the creation of the Worker
s is not associated with the
creation of the tasks and does not provide information about when tasks
were scheduled.
This pool could be used as follows:
import WorkerPool from './worker_pool.js';
import os from 'node:os';
const pool = new WorkerPool(os.availableParallelism());
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
const WorkerPool = require('./worker_pool.js');
const os = require('node:os');
const pool = new WorkerPool(os.availableParallelism());
let finished = 0;
for (let i = 0; i < 10; i++) {
pool.runTask({ a: 42, b: 100 }, (err, result) => {
console.log(i, err, result);
if (++finished === 10)
pool.close();
});
}
Integrating AsyncResource
with EventEmitter
#
Event listeners triggered by an EventEmitter
may be run in a different
execution context than the one that was active when eventEmitter.on()
was
called.
The following example shows how to use the AsyncResource
class to properly
associate an event listener with the correct execution context. The same
approach can be applied to a Stream
or a similar event-driven class.
import { createServer } from 'node:http';
import { AsyncResource, executionAsyncId } from 'node:async_hooks';
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);
const { createServer } = require('node:http');
const { AsyncResource, executionAsyncId } = require('node:async_hooks');
const server = createServer((req, res) => {
req.on('close', AsyncResource.bind(() => {
// Execution context is bound to the current outer scope.
}));
req.on('close', () => {
// Execution context is bound to the scope that caused 'close' to emit.
});
res.end();
}).listen(3000);
Async hooks#
createHook
, AsyncHook
, and
executionAsyncResource
APIs as they have usability issues, safety risks,
and performance implications. Async context tracking use cases are better
served by the stable AsyncLocalStorage
API. If you have a use case for
createHook
, AsyncHook
, or executionAsyncResource
beyond the context
tracking need solved by AsyncLocalStorage
or diagnostics data currently
provided by Diagnostics Channel, please open an issue at
https://github.com/nodejs/node/issues describing your use case so we can
create a more purpose-focused API.Source Code: lib/async_hooks.js
We strongly discourage the use of the async_hooks
API.
Other APIs that can cover most of its use cases include:
AsyncLocalStorage
tracks async contextprocess.getActiveResourcesInfo()
tracks active resources
The node:async_hooks
module provides an API to track asynchronous resources.
It can be accessed using:
import async_hooks from 'node:async_hooks';
const async_hooks = require('node:async_hooks');
Terminology#
An asynchronous resource represents an object with an associated callback.
This callback may be called multiple times, such as the 'connection'
event in net.createServer()
, or just a single time like in fs.open()
.
A resource can also be closed before the callback is called. AsyncHook
does
not explicitly distinguish between these different cases but will represent them
as the abstract concept that is a resource.
If Worker
s are used, each thread has an independent async_hooks
interface, and each thread will use a new set of async IDs.
Overview#
Following is a simple overview of the public API.
import async_hooks from 'node:async_hooks';
// Return the ID of the current execution context.
const eid = async_hooks.executionAsyncId();
// Return the ID of the handle responsible for triggering the callback of the
// current execution scope to call.
const tid = async_hooks.triggerAsyncId();
// Create a new AsyncHook instance. All of these callbacks are optional.
const asyncHook =
async_hooks.createHook({ init, before, after, destroy, promiseResolve });
// Allow callbacks of this AsyncHook instance to call. This is not an implicit
// action after running the constructor, and must be explicitly run to begin
// executing callbacks.
asyncHook.enable();
// Disable listening for new asynchronous events.
asyncHook.disable();
//
// The following are the callbacks that can be passed to createHook().
//
// init() is called during object construction. The resource may not have
// completed construction when this callback runs. Therefore, all fields of the
// resource referenced by "asyncId" may not have been populated.
function init(asyncId, type, triggerAsyncId, resource) { }
// before() is called just before the resource's callback is called. It can be
// called 0-N times for handles (such as TCPWrap), and will be called exactly 1
// time for requests (such as FSReqCallback).
function before(asyncId) { }
// after() is called just after the resource's callback has finished.
function after(asyncId) { }
// destroy() is called when the resource is destroyed.
function destroy(asyncId) { }
// promiseResolve() is called only for promise resources, when the
// resolve() function passed to the Promise constructor is invoked
// (either directly or through other means of resolving a promise).
function promiseResolve(asyncId) { }
const async_hooks = require('node:async_hooks');
// Return the ID of the current execution context.
const eid = async_hooks.executionAsyncId();
// Return the ID of the handle responsible for triggering the callback of the
// current execution scope to call.
const tid = async_hooks.triggerAsyncId();
// Create a new AsyncHook instance. All of these callbacks are optional.
const asyncHook =
async_hooks.createHook({ init, before, after, destroy, promiseResolve });
// Allow callbacks of this AsyncHook instance to call. This is not an implicit
// action after running the constructor, and must be explicitly run to begin
// executing callbacks.
asyncHook.enable();
// Disable listening for new asynchronous events.
asyncHook.disable();
//
// The following are the callbacks that can be passed to createHook().
//
// init() is called during object construction. The resource may not have
// completed construction when this callback runs. Therefore, all fields of the
// resource referenced by "asyncId" may not have been populated.
function init(asyncId, type, triggerAsyncId, resource) { }
// before() is called just before the resource's callback is called. It can be
// called 0-N times for handles (such as TCPWrap), and will be called exactly 1
// time for requests (such as FSReqCallback).
function before(asyncId) { }
// after() is called just after the resource's callback has finished.
function after(asyncId) { }
// destroy() is called when the resource is destroyed.
function destroy(asyncId) { }
// promiseResolve() is called only for promise resources, when the
// resolve() function passed to the Promise constructor is invoked
// (either directly or through other means of resolving a promise).
function promiseResolve(asyncId) { }
async_hooks.createHook(callbacks)
#
callbacks
<Object> The Hook Callbacks to registerinit
<Function> Theinit
callback.before
<Function> Thebefore
callback.after
<Function> Theafter
callback.destroy
<Function> Thedestroy
callback.promiseResolve
<Function> ThepromiseResolve
callback.
- Returns: <AsyncHook> Instance used for disabling and enabling hooks
Registers functions to be called for different lifetime events of each async operation.
The callbacks init()
/before()
/after()
/destroy()
are called for the
respective asynchronous event during a resource's lifetime.
All callbacks are optional. For example, if only resource cleanup needs to
be tracked, then only the destroy
callback needs to be passed. The
specifics of all functions that can be passed to callbacks
is in the
Hook Callbacks section.
import { createHook } from 'node:async_hooks';
const asyncHook = createHook({
init(asyncId, type, triggerAsyncId, resource) { },
destroy(asyncId) { },
});
const async_hooks = require('node:async_hooks');
const asyncHook = async_hooks.createHook({
init(asyncId, type, triggerAsyncId, resource) { },
destroy(asyncId) { },
});
The callbacks will be inherited via the prototype chain:
class MyAsyncCallbacks {
init(asyncId, type, triggerAsyncId, resource) { }
destroy(asyncId) {}
}
class MyAddedCallbacks extends MyAsyncCallbacks {
before(asyncId) { }
after(asyncId) { }
}
const asyncHook = async_hooks.createHook(new MyAddedCallbacks());
Because promises are asynchronous resources whose lifecycle is tracked
via the async hooks mechanism, the init()
, before()
, after()
, and
destroy()
callbacks must not be async functions that return promises.
Error handling#
If any AsyncHook
callbacks throw, the application will print the stack trace
and exit. The exit path does follow that of an uncaught exception, but
all 'uncaughtException'
listeners are removed, thus forcing the process to
exit. The 'exit'
callbacks will still be called unless the application is run
with --abort-on-uncaught-exception
, in which case a stack trace will be
printed and the application exits, leaving a core file.
The reason for this error handling behavior is that these callbacks are running at potentially volatile points in an object's lifetime, for example during class construction and destruction. Because of this, it is deemed necessary to bring down the process quickly in order to prevent an unintentional abort in the future. This is subject to change in the future if a comprehensive analysis is performed to ensure an exception can follow the normal control flow without unintentional side effects.
Printing in AsyncHook
callbacks#
Because printing to the console is an asynchronous operation, console.log()
will cause AsyncHook
callbacks to be called. Using console.log()
or
similar asynchronous operations inside an AsyncHook
callback function will
cause an infinite recursion. An easy solution to this when debugging is to use a
synchronous logging operation such as fs.writeFileSync(file, msg, flag)
.
This will print to the file and will not invoke AsyncHook
recursively because
it is synchronous.
import { writeFileSync } from 'node:fs';
import { format } from 'node:util';
function debug(...args) {
// Use a function like this one when debugging inside an AsyncHook callback
writeFileSync('log.out', `${format(...args)}\n`, { flag: 'a' });
}
const fs = require('node:fs');
const util = require('node:util');
function debug(...args) {
// Use a function like this one when debugging inside an AsyncHook callback
fs.writeFileSync('log.out', `${util.format(...args)}\n`, { flag: 'a' });
}
If an asynchronous operation is needed for logging, it is possible to keep
track of what caused the asynchronous operation using the information
provided by AsyncHook
itself. The logging should then be skipped when
it was the logging itself that caused the AsyncHook
callback to be called. By
doing this, the otherwise infinite recursion is broken.
Class: AsyncHook
#
The class AsyncHook
exposes an interface for tracking lifetime events
of asynchronous operations.
asyncHook.enable()
#
- Returns: <AsyncHook> A reference to
asyncHook
.
Enable the callbacks for a given AsyncHook
instance. If no callbacks are
provided, enabling is a no-op.
The AsyncHook
instance is disabled by default. If the AsyncHook
instance
should be enabled immediately after creation, the following pattern can be used.
import { createHook } from 'node:async_hooks';
const hook = createHook(callbacks).enable();
const async_hooks = require('node:async_hooks');
const hook = async_hooks.createHook(callbacks).enable();
asyncHook.disable()
#
- Returns: <AsyncHook> A reference to
asyncHook
.
Disable the callbacks for a given AsyncHook
instance from the global pool of
AsyncHook
callbacks to be executed. Once a hook has been disabled it will not
be called again until enabled.
For API consistency disable()
also returns the AsyncHook
instance.
Hook callbacks#
Key events in the lifetime of asynchronous events have been categorized into four areas: instantiation, before/after the callback is called, and when the instance is destroyed.
init(asyncId, type, triggerAsyncId, resource)
#
asyncId
<number> A unique ID for the async resource.type
<string> The type of the async resource.triggerAsyncId
<number> The unique ID of the async resource in whose execution context this async resource was created.resource
<Object> Reference to the resource representing the async operation, needs to be released during destroy.
Called when a class is constructed that has the possibility to emit an
asynchronous event. This does not mean the instance must call
before
/after
before destroy
is called, only that the possibility
exists.
This behavior can be observed by doing something like opening a resource then closing it before the resource can be used. The following snippet demonstrates this.
import { createServer } from 'node:net';
createServer().listen(function() { this.close(); });
// OR
clearTimeout(setTimeout(() => {}, 10));
require('node:net').createServer().listen(function() { this.close(); });
// OR
clearTimeout(setTimeout(() => {}, 10));
Every new resource is assigned an ID that is unique within the scope of the current Node.js instance.
type
#
The type
is a string identifying the type of resource that caused
init
to be called. Generally, it will correspond to the name of the
resource's constructor.
The type
of resources created by Node.js itself can change in any Node.js
release. Valid values include TLSWRAP
,
TCPWRAP
, TCPSERVERWRAP
, GETADDRINFOREQWRAP
, FSREQCALLBACK
,
Microtask
, and Timeout
. Inspect the source code of the Node.js version used
to get the full list.
Furthermore users of AsyncResource
create async resources independent
of Node.js itself.
There is also the PROMISE
resource type, which is used to track Promise
instances and asynchronous work scheduled by them.
Users are able to define their own type
when using the public embedder API.
It is possible to have type name collisions. Embedders are encouraged to use unique prefixes, such as the npm package name, to prevent collisions when listening to the hooks.
triggerAsyncId
#
triggerAsyncId
is the asyncId
of the resource that caused (or "triggered")
the new resource to initialize and that caused init
to call. This is different
from async_hooks.executionAsyncId()
that only shows when a resource was
created, while triggerAsyncId
shows why a resource was created.
The following is a simple demonstration of triggerAsyncId
:
import { createHook, executionAsyncId } from 'node:async_hooks';
import { stdout } from 'node:process';
import net from 'node:net';
import fs from 'node:fs';
createHook({
init(asyncId, type, triggerAsyncId) {
const eid = executionAsyncId();
fs.writeSync(
stdout.fd,
`${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
}).enable();
net.createServer((conn) => {}).listen(8080);
const { createHook, executionAsyncId } = require('node:async_hooks');
const { stdout } = require('node:process');
const net = require('node:net');
const fs = require('node:fs');
createHook({
init(asyncId, type, triggerAsyncId) {
const eid = executionAsyncId();
fs.writeSync(
stdout.fd,
`${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
}).enable();
net.createServer((conn) => {}).listen(8080);
Output when hitting the server with nc localhost 8080
:
TCPSERVERWRAP(5): trigger: 1 execution: 1
TCPWRAP(7): trigger: 5 execution: 0
The TCPSERVERWRAP
is the server which receives the connections.
The TCPWRAP
is the new connection from the client. When a new
connection is made, the TCPWrap
instance is immediately constructed. This
happens outside of any JavaScript stack. (An executionAsyncId()
of 0
means
that it is being executed from C++ with no JavaScript stack above it.) With only
that information, it would be impossible to link resources together in
terms of what caused them to be created, so triggerAsyncId
is given the task
of propagating what resource is responsible for the new resource's existence.
resource
#
resource
is an object that represents the actual async resource that has
been initialized. The API to access the object may be specified by the
creator of the resource. Resources created by Node.js itself are internal
and may change at any time. Therefore no API is specified for these.
In some cases the resource object is reused for performance reasons, it is
thus not safe to use it as a key in a WeakMap
or add properties to it.
Asynchronous context example#
The context tracking use case is covered by the stable API AsyncLocalStorage
.
This example only illustrates async hooks operation but AsyncLocalStorage
fits better to this use case.
The following is an example with additional information about the calls to
init
between the before
and after
calls, specifically what the
callback to listen()
will look like. The output formatting is slightly more
elaborate to make calling context easier to see.
import async_hooks from 'node:async_hooks';
import fs from 'node:fs';
import net from 'node:net';
import { stdout } from 'node:process';
const { fd } = stdout;
let indent = 0;
async_hooks.createHook({
init(asyncId, type, triggerAsyncId) {
const eid = async_hooks.executionAsyncId();
const indentStr = ' '.repeat(indent);
fs.writeSync(
fd,
`${indentStr}${type}(${asyncId}):` +
` trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
before(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}before: ${asyncId}\n`);
indent += 2;
},
after(asyncId) {
indent -= 2;
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}after: ${asyncId}\n`);
},
destroy(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}destroy: ${asyncId}\n`);
},
}).enable();
net.createServer(() => {}).listen(8080, () => {
// Let's wait 10ms before logging the server started.
setTimeout(() => {
console.log('>>>', async_hooks.executionAsyncId());
}, 10);
});
const async_hooks = require('node:async_hooks');
const fs = require('node:fs');
const net = require('node:net');
const { fd } = process.stdout;
let indent = 0;
async_hooks.createHook({
init(asyncId, type, triggerAsyncId) {
const eid = async_hooks.executionAsyncId();
const indentStr = ' '.repeat(indent);
fs.writeSync(
fd,
`${indentStr}${type}(${asyncId}):` +
` trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
before(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}before: ${asyncId}\n`);
indent += 2;
},
after(asyncId) {
indent -= 2;
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}after: ${asyncId}\n`);
},
destroy(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(fd, `${indentStr}destroy: ${asyncId}\n`);
},
}).enable();
net.createServer(() => {}).listen(8080, () => {
// Let's wait 10ms before logging the server started.
setTimeout(() => {
console.log('>>>', async_hooks.executionAsyncId());
}, 10);
});
Output from only starting the server:
TCPSERVERWRAP(5): trigger: 1 execution: 1
TickObject(6): trigger: 5 execution: 1
before: 6
Timeout(7): trigger: 6 execution: 6
after: 6
destroy: 6
before: 7
>>> 7
TickObject(8): trigger: 7 execution: 7
after: 7
before: 8
after: 8
As illustrated in the example, executionAsyncId()
and execution
each specify
the value of the current execution context; which is delineated by calls to
before
and after
.
Only using execution
to graph resource allocation results in the following:
root(1)
^
|
TickObject(6)
^
|
Timeout(7)
The TCPSERVERWRAP
is not part of this graph, even though it was the reason for
console.log()
being called. This is because binding to a port without a host
name is a synchronous operation, but to maintain a completely asynchronous
API the user's callback is placed in a process.nextTick()
. Which is why
TickObject
is present in the output and is a 'parent' for .listen()
callback.
The graph only shows when a resource was created, not why, so to track
the why use triggerAsyncId
. Which can be represented with the following
graph:
bootstrap(1)
|
Ë…
TCPSERVERWRAP(5)
|
Ë…
TickObject(6)
|
Ë…
Timeout(7)
before(asyncId)
#
asyncId
<number>
When an asynchronous operation is initiated (such as a TCP server receiving a
new connection) or completes (such as writing data to disk) a callback is
called to notify the user. The before
callback is called just before said
callback is executed. asyncId
is the unique identifier assigned to the
resource about to execute the callback.
The before
callback will be called 0 to N times. The before
callback
will typically be called 0 times if the asynchronous operation was cancelled
or, for example, if no connections are received by a TCP server. Persistent
asynchronous resources like a TCP server will typically call the before
callback multiple times, while other operations like fs.open()
will call
it only once.
after(asyncId)
#
asyncId
<number>
Called immediately after the callback specified in before
is completed.
If an uncaught exception occurs during execution of the callback, then after
will run after the 'uncaughtException'
event is emitted or a domain
's
handler runs.
destroy(asyncId)
#
asyncId
<number>
Called after the resource corresponding to asyncId
is destroyed. It is also
called asynchronously from the embedder API emitDestroy()
.
Some resources depend on garbage collection for cleanup, so if a reference is
made to the resource
object passed to init
it is possible that destroy
will never be called, causing a memory leak in the application. If the resource
does not depend on garbage collection, then this will not be an issue.
Using the destroy hook results in additional overhead because it enables
tracking of Promise
instances via the garbage collector.
promiseResolve(asyncId)
#
asyncId
<number>
Called when the resolve
function passed to the Promise
constructor is
invoked (either directly or through other means of resolving a promise).
resolve()
does not do any observable synchronous work.
The Promise
is not necessarily fulfilled or rejected at this point if the
Promise
was resolved by assuming the state of another Promise
.
new Promise((resolve) => resolve(true)).then((a) => {});
calls the following callbacks:
init for PROMISE with id 5, trigger id: 1
promise resolve 5 # corresponds to resolve(true)
init for PROMISE with id 6, trigger id: 5 # the Promise returned by then()
before 6 # the then() callback is entered
promise resolve 6 # the then() callback resolves the promise by returning
after 6
async_hooks.executionAsyncResource()
#
- Returns: <Object> The resource representing the current execution. Useful to store data within the resource.
Resource objects returned by executionAsyncResource()
are most often internal
Node.js handle objects with undocumented APIs. Using any functions or properties
on the object is likely to crash your application and should be avoided.
Using executionAsyncResource()
in the top-level execution context will
return an empty object as there is no handle or request object to use,
but having an object representing the top-level can be helpful.
import { open } from 'node:fs';
import { executionAsyncId, executionAsyncResource } from 'node:async_hooks';
console.log(executionAsyncId(), executionAsyncResource()); // 1 {}
open(new URL(import.meta.url), 'r', (err, fd) => {
console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap
});
const { open } = require('node:fs');
const { executionAsyncId, executionAsyncResource } = require('node:async_hooks');
console.log(executionAsyncId(), executionAsyncResource()); // 1 {}
open(__filename, 'r', (err, fd) => {
console.log(executionAsyncId(), executionAsyncResource()); // 7 FSReqWrap
});
This can be used to implement continuation local storage without the
use of a tracking Map
to store the metadata:
import { createServer } from 'node:http';
import {
executionAsyncId,
executionAsyncResource,
createHook,
} from 'async_hooks';
const sym = Symbol('state'); // Private symbol to avoid pollution
createHook({
init(asyncId, type, triggerAsyncId, resource) {
const cr = executionAsyncResource();
if (cr) {
resource[sym] = cr[sym];
}
},
}).enable();
const server = createServer((req, res) => {
executionAsyncResource()[sym] = { state: req.url };
setTimeout(function() {
res.end(JSON.stringify(executionAsyncResource()[sym]));
}, 100);
}).listen(3000);
const { createServer } = require('node:http');
const {
executionAsyncId,
executionAsyncResource,
createHook,
} = require('node:async_hooks');
const sym = Symbol('state'); // Private symbol to avoid pollution
createHook({
init(asyncId, type, triggerAsyncId, resource) {
const cr = executionAsyncResource();
if (cr) {
resource[sym] = cr[sym];
}
},
}).enable();
const server = createServer((req, res) => {
executionAsyncResource()[sym] = { state: req.url };
setTimeout(function() {
res.end(JSON.stringify(executionAsyncResource()[sym]));
}, 100);
}).listen(3000);
async_hooks.executionAsyncId()
#
- Returns: <number> The
asyncId
of the current execution context. Useful to track when something calls.
import { executionAsyncId } from 'node:async_hooks';
import fs from 'node:fs';
console.log(executionAsyncId()); // 1 - bootstrap
const path = '.';
fs.open(path, 'r', (err, fd) => {
console.log(executionAsyncId()); // 6 - open()
});
const async_hooks = require('node:async_hooks');
const fs = require('node:fs');
console.log(async_hooks.executionAsyncId()); // 1 - bootstrap
const path = '.';
fs.open(path, 'r', (err, fd) => {
console.log(async_hooks.executionAsyncId()); // 6 - open()
});
The ID returned from executionAsyncId()
is related to execution timing, not
causality (which is covered by triggerAsyncId()
):
const server = net.createServer((conn) => {
// Returns the ID of the server, not of the new connection, because the
// callback runs in the execution scope of the server's MakeCallback().
async_hooks.executionAsyncId();
}).listen(port, () => {
// Returns the ID of a TickObject (process.nextTick()) because all
// callbacks passed to .listen() are wrapped in a nextTick().
async_hooks.executionAsyncId();
});
Promise contexts may not get precise executionAsyncIds
by default.
See the section on promise execution tracking.
async_hooks.triggerAsyncId()
#
- Returns: <number> The ID of the resource responsible for calling the callback that is currently being executed.
const server = net.createServer((conn) => {
// The resource that caused (or triggered) this callback to be called
// was that of the new connection. Thus the return value of triggerAsyncId()
// is the asyncId of "conn".
async_hooks.triggerAsyncId();
}).listen(port, () => {
// Even though all callbacks passed to .listen() are wrapped in a nextTick()
// the callback itself exists because the call to the server's .listen()
// was made. So the return value would be the ID of the server.
async_hooks.triggerAsyncId();
});
Promise contexts may not get valid triggerAsyncId
s by default. See
the section on promise execution tracking.
async_hooks.asyncWrapProviders
#
- Returns: A map of provider types to the corresponding numeric id.
This map contains all the event types that might be emitted by the
async_hooks.init()
event.
This feature suppresses the deprecated usage of process.binding('async_wrap').Providers
.
See: DEP0111
Promise execution tracking#
By default, promise executions are not assigned asyncId
s due to the relatively
expensive nature of the promise introspection API provided by
V8. This means that programs using promises or async
/await
will not get
correct execution and trigger ids for promise callback contexts by default.
import { executionAsyncId, triggerAsyncId } from 'node:async_hooks';
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 1 tid 0
const { executionAsyncId, triggerAsyncId } = require('node:async_hooks');
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 1 tid 0
Observe that the then()
callback claims to have executed in the context of the
outer scope even though there was an asynchronous hop involved. Also,
the triggerAsyncId
value is 0
, which means that we are missing context about
the resource that caused (triggered) the then()
callback to be executed.
Installing async hooks via async_hooks.createHook
enables promise execution
tracking:
import { createHook, executionAsyncId, triggerAsyncId } from 'node:async_hooks';
createHook({ init() {} }).enable(); // forces PromiseHooks to be enabled.
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 7 tid 6
const { createHook, executionAsyncId, triggerAsyncId } = require('node:async_hooks');
createHook({ init() {} }).enable(); // forces PromiseHooks to be enabled.
Promise.resolve(1729).then(() => {
console.log(`eid ${executionAsyncId()} tid ${triggerAsyncId()}`);
});
// produces:
// eid 7 tid 6
In this example, adding any actual hook function enabled the tracking of
promises. There are two promises in the example above; the promise created by
Promise.resolve()
and the promise returned by the call to then()
. In the
example above, the first promise got the asyncId
6
and the latter got
asyncId
7
. During the execution of the then()
callback, we are executing
in the context of promise with asyncId
7
. This promise was triggered by
async resource 6
.
Another subtlety with promises is that before
and after
callbacks are run
only on chained promises. That means promises not created by then()
/catch()
will not have the before
and after
callbacks fired on them. For more details
see the details of the V8 PromiseHooks API.
JavaScript embedder API#
Library developers that handle their own asynchronous resources performing tasks
like I/O, connection pooling, or managing callback queues may use the
AsyncResource
JavaScript API so that all the appropriate callbacks are called.
Class: AsyncResource
#
The documentation for this class has moved AsyncResource
.
Class: AsyncLocalStorage
#
The documentation for this class has moved AsyncLocalStorage
.
Buffer#
Source Code: lib/buffer.js
Buffer
objects are used to represent a fixed-length sequence of bytes. Many
Node.js APIs support Buffer
s.
The Buffer
class is a subclass of JavaScript's Uint8Array
class and
extends it with methods that cover additional use cases. Node.js APIs accept
plain Uint8Array
s wherever Buffer
s are supported as well.
While the Buffer
class is available within the global scope, it is still
recommended to explicitly reference it via an import or require statement.
import { Buffer } from 'node:buffer';
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);
// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');
// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
const { Buffer } = require('node:buffer');
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10,
// filled with bytes which all have the value `1`.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using fill(), write(), or other functions that fill the Buffer's
// contents.
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing the bytes [1, 2, 3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing the bytes [1, 1, 1, 1] – the entries
// are all truncated using `(value & 255)` to fit into the range 0–255.
const buf5 = Buffer.from([257, 257.5, -255, '1']);
// Creates a Buffer containing the UTF-8-encoded bytes for the string 'tést':
// [0x74, 0xc3, 0xa9, 0x73, 0x74] (in hexadecimal notation)
// [116, 195, 169, 115, 116] (in decimal notation)
const buf6 = Buffer.from('tést');
// Creates a Buffer containing the Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf7 = Buffer.from('tést', 'latin1');
Buffers and character encodings#
When converting between Buffer
s and strings, a character encoding may be
specified. If no character encoding is specified, UTF-8 will be used as the
default.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('hello world', 'utf8');
console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=
console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
const { Buffer } = require('node:buffer');
const buf = Buffer.from('hello world', 'utf8');
console.log(buf.toString('hex'));
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('base64'));
// Prints: aGVsbG8gd29ybGQ=
console.log(Buffer.from('fhqwhgads', 'utf8'));
// Prints: <Buffer 66 68 71 77 68 67 61 64 73>
console.log(Buffer.from('fhqwhgads', 'utf16le'));
// Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
Node.js buffers accept all case variations of encoding strings that they
receive. For example, UTF-8 can be specified as 'utf8'
, 'UTF8'
, or 'uTf8'
.
The character encodings currently supported by Node.js are the following:
-
'utf8'
(alias:'utf-8'
): Multi-byte encoded Unicode characters. Many web pages and other document formats use UTF-8. This is the default character encoding. When decoding aBuffer
into a string that does not exclusively contain valid UTF-8 data, the Unicode replacement characterU+FFFD
� will be used to represent those errors. -
'utf16le'
(alias:'utf-16le'
): Multi-byte encoded Unicode characters. Unlike'utf8'
, each character in the string will be encoded using either 2 or 4 bytes. Node.js only supports the little-endian variant of UTF-16. -
'latin1'
: Latin-1 stands for ISO-8859-1. This character encoding only supports the Unicode characters fromU+0000
toU+00FF
. Each character is encoded using a single byte. Characters that do not fit into that range are truncated and will be mapped to characters in that range.
Converting a Buffer
into a string using one of the above is referred to as
decoding, and converting a string into a Buffer
is referred to as encoding.
Node.js also supports the following binary-to-text encodings. For
binary-to-text encodings, the naming convention is reversed: Converting a
Buffer
into a string is typically referred to as encoding, and converting a
string into a Buffer
as decoding.
-
'base64'
: Base64 encoding. When creating aBuffer
from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC 4648, Section 5. Whitespace characters such as spaces, tabs, and new lines contained within the base64-encoded string are ignored. -
'base64url'
: base64url encoding as specified in RFC 4648, Section 5. When creating aBuffer
from a string, this encoding will also correctly accept regular base64-encoded strings. When encoding aBuffer
to a string, this encoding will omit padding. -
'hex'
: Encode each byte as two hexadecimal characters. Data truncation may occur when decoding strings that do not exclusively consist of an even number of hexadecimal characters. See below for an example.
The following legacy character encodings are also supported:
-
'ascii'
: For 7-bit ASCII data only. When encoding a string into aBuffer
, this is equivalent to using'latin1'
. When decoding aBuffer
into a string, using this encoding will additionally unset the highest bit of each byte before decoding as'latin1'
. Generally, there should be no reason to use this encoding, as'utf8'
(or, if the data is known to always be ASCII-only,'latin1'
) will be a better choice when encoding or decoding ASCII-only text. It is only provided for legacy compatibility. -
'binary'
: Alias for'latin1'
. The name of this encoding can be very misleading, as all of the encodings listed here convert between strings and binary data. For converting between strings andBuffer
s, typically'utf8'
is the right choice. -
'ucs2'
,'ucs-2'
: Aliases of'utf16le'
. UCS-2 used to refer to a variant of UTF-16 that did not support characters that had code points larger than U+FFFF. In Node.js, these code points are always supported.
import { Buffer } from 'node:buffer';
Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.
Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').
Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
const { Buffer } = require('node:buffer');
Buffer.from('1ag123', 'hex');
// Prints <Buffer 1a>, data truncated when first non-hexadecimal value
// ('g') encountered.
Buffer.from('1a7', 'hex');
// Prints <Buffer 1a>, data truncated when data ends in single digit ('7').
Buffer.from('1634', 'hex');
// Prints <Buffer 16 34>, all data represented.
Modern Web browsers follow the WHATWG Encoding Standard which aliases
both 'latin1'
and 'ISO-8859-1'
to 'win-1252'
. This means that while doing
something like http.get()
, if the returned charset is one of those listed in
the WHATWG specification it is possible that the server actually returned
'win-1252'
-encoded data, and using 'latin1'
encoding may incorrectly decode
the characters.
Buffers and TypedArrays#
Buffer
instances are also JavaScript Uint8Array
and TypedArray
instances. All TypedArray
methods are available on Buffer
s. There are,
however, subtle incompatibilities between the Buffer
API and the
TypedArray
API.
In particular:
- While
TypedArray.prototype.slice()
creates a copy of part of theTypedArray
,Buffer.prototype.slice()
creates a view over the existingBuffer
without copying. This behavior can be surprising, and only exists for legacy compatibility.TypedArray.prototype.subarray()
can be used to achieve the behavior ofBuffer.prototype.slice()
on bothBuffer
s and otherTypedArray
s and should be preferred. buf.toString()
is incompatible with itsTypedArray
equivalent.- A number of methods, e.g.
buf.indexOf()
, support additional arguments.
There are two ways to create new TypedArray
instances from a Buffer
:
- Passing a
Buffer
to aTypedArray
constructor will copy theBuffer
s contents, interpreted as an array of integers, and not as a byte sequence of the target type.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);
console.log(uint32array);
// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
const uint32array = new Uint32Array(buf);
console.log(uint32array);
// Prints: Uint32Array(4) [ 1, 2, 3, 4 ]
- Passing the
Buffer
s underlyingArrayBuffer
will create aTypedArray
that shares its memory with theBuffer
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
buf.buffer,
buf.byteOffset,
buf.length / Uint16Array.BYTES_PER_ELEMENT);
console.log(uint16array);
// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
const { Buffer } = require('node:buffer');
const buf = Buffer.from('hello', 'utf16le');
const uint16array = new Uint16Array(
buf.buffer,
buf.byteOffset,
buf.length / Uint16Array.BYTES_PER_ELEMENT);
console.log(uint16array);
// Prints: Uint16Array(5) [ 104, 101, 108, 108, 111 ]
It is possible to create a new Buffer
that shares the same allocated
memory as a TypedArray
instance by using the TypedArray
object's
.buffer
property in the same way. Buffer.from()
behaves like new Uint8Array()
in this context.
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
When creating a Buffer
using a TypedArray
's .buffer
, it is
possible to use only a portion of the underlying ArrayBuffer
by passing in
byteOffset
and length
parameters.
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
// Prints: 16
The Buffer.from()
and TypedArray.from()
have different signatures and
implementations. Specifically, the TypedArray
variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:
TypedArray.from(source[, mapFn[, thisArg]])
The Buffer.from()
method, however, does not support the use of a mapping
function:
Buffers and iteration#
Buffer
instances can be iterated over using for..of
syntax:
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3]);
for (const b of buf) {
console.log(b);
}
// Prints:
// 1
// 2
// 3
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3]);
for (const b of buf) {
console.log(b);
}
// Prints:
// 1
// 2
// 3
Additionally, the buf.values()
, buf.keys()
, and
buf.entries()
methods can be used to create iterators.
Class: Blob
#
A Blob
encapsulates immutable, raw data that can be safely shared across
multiple worker threads.
new buffer.Blob([sources[, options]])
#
sources
<string[]> | <ArrayBuffer[]> | <TypedArray[]> | <DataView[]> | <Blob[]> An array of string, <ArrayBuffer>, <TypedArray>, <DataView>, or <Blob> objects, or any mix of such objects, that will be stored within theBlob
.options
<Object>endings
<string> One of either'transparent'
or'native'
. When set to'native'
, line endings in string source parts will be converted to the platform native line-ending as specified byrequire('node:os').EOL
.type
<string> The Blob content-type. The intent is fortype
to convey the MIME media type of the data, however no validation of the type format is performed.
Creates a new Blob
object containing a concatenation of the given sources.
<ArrayBuffer>, <TypedArray>, <DataView>, and <Buffer> sources are copied into the 'Blob' and can therefore be safely modified after the 'Blob' is created.
String sources are encoded as UTF-8 byte sequences and copied into the Blob. Unmatched surrogate pairs within each string part will be replaced by Unicode U+FFFD replacement characters.
blob.arrayBuffer()
#
- Returns: <Promise>
Returns a promise that fulfills with an <ArrayBuffer> containing a copy of
the Blob
data.
blob.size
#
The total size of the Blob
in bytes.
blob.slice([start[, end[, type]]])
#
start
<number> The starting index.end
<number> The ending index.type
<string> The content-type for the newBlob
Creates and returns a new Blob
containing a subset of this Blob
objects
data. The original Blob
is not altered.
blob.stream()
#
- Returns: <ReadableStream>
Returns a new ReadableStream
that allows the content of the Blob
to be read.
blob.text()
#
- Returns: <Promise>
Returns a promise that fulfills with the contents of the Blob
decoded as a
UTF-8 string.
blob.type
#
- Type: <string>
The content-type of the Blob
.
Blob
objects and MessageChannel
#
Once a <Blob> object is created, it can be sent via MessagePort
to multiple
destinations without transferring or immediately copying the data. The data
contained by the Blob
is copied only when the arrayBuffer()
or text()
methods are called.
import { Blob } from 'node:buffer';
import { setTimeout as delay } from 'node:timers/promises';
const blob = new Blob(['hello there']);
const mc1 = new MessageChannel();
const mc2 = new MessageChannel();
mc1.port1.onmessage = async ({ data }) => {
console.log(await data.arrayBuffer());
mc1.port1.close();
};
mc2.port1.onmessage = async ({ data }) => {
await delay(1000);
console.log(await data.arrayBuffer());
mc2.port1.close();
};
mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);
// The Blob is still usable after posting.
blob.text().then(console.log);
const { Blob } = require('node:buffer');
const { setTimeout: delay } = require('node:timers/promises');
const blob = new Blob(['hello there']);
const mc1 = new MessageChannel();
const mc2 = new MessageChannel();
mc1.port1.onmessage = async ({ data }) => {
console.log(await data.arrayBuffer());
mc1.port1.close();
};
mc2.port1.onmessage = async ({ data }) => {
await delay(1000);
console.log(await data.arrayBuffer());
mc2.port1.close();
};
mc1.port2.postMessage(blob);
mc2.port2.postMessage(blob);
// The Blob is still usable after posting.
blob.text().then(console.log);
Class: Buffer
#
The Buffer
class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
Static method: Buffer.alloc(size[, fill[, encoding]])
#
size
<integer> The desired length of the newBuffer
.fill
<string> | <Buffer> | <Uint8Array> | <integer> A value to pre-fill the newBuffer
with. Default:0
.encoding
<string> Iffill
is a string, this is its encoding. Default:'utf8'
.
Allocates a new Buffer
of size
bytes. If fill
is undefined
, the
Buffer
will be zero-filled.
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00>
If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_OUT_OF_RANGE
is thrown.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
.
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(5, 'a');
console.log(buf);
// Prints: <Buffer 61 61 61 61 61>
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
.
import { Buffer } from 'node:buffer';
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
const { Buffer } = require('node:buffer');
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
Calling Buffer.alloc()
can be measurably slower than the alternative
Buffer.allocUnsafe()
but ensures that the newly created Buffer
instance
contents will never contain sensitive data from previous allocations, including
data that might not have been allocated for Buffer
s.
A TypeError
will be thrown if size
is not a number.
Static method: Buffer.allocUnsafe(size)
#
size
<integer> The desired length of the newBuffer
.
Allocates a new Buffer
of size
bytes. If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_OUT_OF_RANGE
is thrown.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use Buffer.alloc()
instead to initialize
Buffer
instances with zeroes.
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(10);
console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
buf.fill(0);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(10);
console.log(buf);
// Prints (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
buf.fill(0);
console.log(buf);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
A TypeError
will be thrown if size
is not a number.
The Buffer
module pre-allocates an internal Buffer
instance of
size Buffer.poolSize
that is used as a pool for the fast allocation of new
Buffer
instances created using Buffer.allocUnsafe()
, Buffer.from(array)
,
and Buffer.concat()
only when size
is less than or equal to
Buffer.poolSize >> 1
(floor of Buffer.poolSize
divided by two).
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill)
vs. Buffer.allocUnsafe(size).fill(fill)
.
Specifically, Buffer.alloc(size, fill)
will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill)
will use the internal
Buffer
pool if size
is less than or equal to half Buffer.poolSize
. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe()
provides.
Static method: Buffer.allocUnsafeSlow(size)
#
size
<integer> The desired length of the newBuffer
.
Allocates a new Buffer
of size
bytes. If size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, ERR_OUT_OF_RANGE
is thrown. A zero-length Buffer
is created if size
is 0.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use buf.fill(0)
to initialize
such Buffer
instances with zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4 KiB are sliced from a single pre-allocated Buffer
. This
allows applications to avoid the garbage collection overhead of creating many
individually allocated Buffer
instances. This approach improves both
performance and memory usage by eliminating the need to track and clean up as
many individual ArrayBuffer
objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer
instance using Buffer.allocUnsafeSlow()
and
then copying out the relevant bits.
import { Buffer } from 'node:buffer';
// Need to keep around a few small chunks of memory.
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
// Allocate for retained data.
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation.
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});
const { Buffer } = require('node:buffer');
// Need to keep around a few small chunks of memory.
const store = [];
socket.on('readable', () => {
let data;
while (null !== (data = readable.read())) {
// Allocate for retained data.
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation.
data.copy(sb, 0, 0, 10);
store.push(sb);
}
});
A TypeError
will be thrown if size
is not a number.
Static method: Buffer.byteLength(string[, encoding])
#
string
<string> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> | <SharedArrayBuffer> A value to calculate the length of.encoding
<string> Ifstring
is a string, this is its encoding. Default:'utf8'
.- Returns: <integer> The number of bytes contained within
string
.
Returns the byte length of a string when encoded using encoding
.
This is not the same as String.prototype.length
, which does not account
for the encoding that is used to convert the string into bytes.
For 'base64'
, 'base64url'
, and 'hex'
, this function assumes valid input.
For strings that contain non-base64/hex-encoded data (e.g. whitespace), the
return value might be greater than the length of a Buffer
created from the
string.
import { Buffer } from 'node:buffer';
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
const { Buffer } = require('node:buffer');
const str = '\u00bd + \u00bc = \u00be';
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
/
SharedArrayBuffer
, the byte length as reported by .byteLength
is returned.
Static method: Buffer.compare(buf1, buf2)
#
buf1
<Buffer> | <Uint8Array>buf2
<Buffer> | <Uint8Array>- Returns: <integer> Either
-1
,0
, or1
, depending on the result of the comparison. Seebuf.compare()
for details.
Compares buf1
to buf2
, typically for the purpose of sorting arrays of
Buffer
instances. This is equivalent to calling
buf1.compare(buf2)
.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
console.log(arr.sort(Buffer.compare));
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1].)
Static method: Buffer.concat(list[, totalLength])
#
list
<Buffer[]> | <Uint8Array[]> List ofBuffer
orUint8Array
instances to concatenate.totalLength
<integer> Total length of theBuffer
instances inlist
when concatenated.- Returns: <Buffer>
Returns a new Buffer
which is the result of concatenating all the Buffer
instances in the list
together.
If the list has no items, or if the totalLength
is 0, then a new zero-length
Buffer
is returned.
If totalLength
is not provided, it is calculated from the Buffer
instances
in list
by adding their lengths.
If totalLength
is provided, it is coerced to an unsigned integer. If the
combined length of the Buffer
s in list
exceeds totalLength
, the result is
truncated to totalLength
.
import { Buffer } from 'node:buffer';
// Create a single `Buffer` from a list of three `Buffer` instances.
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
// Prints: 42
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
const { Buffer } = require('node:buffer');
// Create a single `Buffer` from a list of three `Buffer` instances.
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
console.log(totalLength);
// Prints: 42
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
console.log(bufA);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA.length);
// Prints: 42
Buffer.concat()
may also use the internal Buffer
pool like
Buffer.allocUnsafe()
does.
Static method: Buffer.copyBytesFrom(view[, offset[, length]])
#
view
<TypedArray> The <TypedArray> to copy.offset
<integer> The starting offset withinview
. Default::0
.length
<integer> The number of elements fromview
to copy. Default:view.length - offset
.
Copies the underlying memory of view
into a new Buffer
.
const u16 = new Uint16Array([0, 0xffff]);
const buf = Buffer.copyBytesFrom(u16, 1, 1);
u16[1] = 0;
console.log(buf.length); // 2
console.log(buf[0]); // 255
console.log(buf[1]); // 255
Static method: Buffer.from(array)
#
array
<integer[]>
Allocates a new Buffer
using an array
of bytes in the range 0
– 255
.
Array entries outside that range will be truncated to fit into it.
import { Buffer } from 'node:buffer';
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'.
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
const { Buffer } = require('node:buffer');
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'.
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
If array
is an Array
-like object (that is, one with a length
property of
type number
), it is treated as if it is an array, unless it is a Buffer
or
a Uint8Array
. This means all other TypedArray
variants get treated as an
Array
. To create a Buffer
from the bytes backing a TypedArray
, use
Buffer.copyBytesFrom()
.
A TypeError
will be thrown if array
is not an Array
or another type
appropriate for Buffer.from()
variants.
Buffer.from(array)
and Buffer.from(string)
may also use the internal
Buffer
pool like Buffer.allocUnsafe()
does.
Static method: Buffer.from(arrayBuffer[, byteOffset[, length]])
#
arrayBuffer
<ArrayBuffer> | <SharedArrayBuffer> AnArrayBuffer
,SharedArrayBuffer
, for example the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
.length
<integer> Number of bytes to expose. Default:arrayBuffer.byteLength - byteOffset
.
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
's underlying ArrayBuffer
.
import { Buffer } from 'node:buffer';
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
const { Buffer } = require('node:buffer');
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`.
const buf = Buffer.from(arr.buffer);
console.log(buf);
// Prints: <Buffer 88 13 a0 0f>
// Changing the original Uint16Array changes the Buffer also.
arr[1] = 6000;
console.log(buf);
// Prints: <Buffer 88 13 70 17>
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
import { Buffer } from 'node:buffer';
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
const { Buffer } = require('node:buffer');
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
// Prints: 2
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
or a
SharedArrayBuffer
or another type appropriate for Buffer.from()
variants.
It is important to remember that a backing ArrayBuffer
can cover a range
of memory that extends beyond the bounds of a TypedArray
view. A new
Buffer
created using the buffer
property of a TypedArray
may extend
beyond the range of the TypedArray
:
import { Buffer } from 'node:buffer';
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true
const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
const { Buffer } = require('node:buffer');
const arrA = Uint8Array.from([0x63, 0x64, 0x65, 0x66]); // 4 elements
const arrB = new Uint8Array(arrA.buffer, 1, 2); // 2 elements
console.log(arrA.buffer === arrB.buffer); // true
const buf = Buffer.from(arrB.buffer);
console.log(buf);
// Prints: <Buffer 63 64 65 66>
Static method: Buffer.from(buffer)
#
buffer
<Buffer> | <Uint8Array> An existingBuffer
orUint8Array
from which to copy data.
Copies the passed buffer
data onto a new Buffer
instance.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
console.log(buf1.toString());
// Prints: auffer
console.log(buf2.toString());
// Prints: buffer
A TypeError
will be thrown if buffer
is not a Buffer
or another type
appropriate for Buffer.from()
variants.
Static method: Buffer.from(object[, offsetOrEncoding[, length]])
#
object
<Object> An object supportingSymbol.toPrimitive
orvalueOf()
.offsetOrEncoding
<integer> | <string> A byte-offset or encoding.length
<integer> A length.
For objects whose valueOf()
function returns a value not strictly equal to
object
, returns Buffer.from(object.valueOf(), offsetOrEncoding, length)
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
const { Buffer } = require('node:buffer');
const buf = Buffer.from(new String('this is a test'));
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
For objects that support Symbol.toPrimitive
, returns
Buffer.from(object[Symbol.toPrimitive]('string'), offsetOrEncoding)
.
import { Buffer } from 'node:buffer';
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
const { Buffer } = require('node:buffer');
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// Prints: <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
A TypeError
will be thrown if object
does not have the mentioned methods or
is not of another type appropriate for Buffer.from()
variants.
Static method: Buffer.from(string[, encoding])
#
Creates a new Buffer
containing string
. The encoding
parameter identifies
the character encoding to be used when converting string
into bytes.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tést
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('this is a tést');
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf1.toString());
// Prints: this is a tést
console.log(buf2.toString());
// Prints: this is a tést
console.log(buf1.toString('latin1'));
// Prints: this is a tést
A TypeError
will be thrown if string
is not a string or another type
appropriate for Buffer.from()
variants.
Static method: Buffer.isBuffer(obj)
#
Returns true
if obj
is a Buffer
, false
otherwise.
import { Buffer } from 'node:buffer';
Buffer.isBuffer(Buffer.alloc(10)); // true
Buffer.isBuffer(Buffer.from('foo')); // true
Buffer.isBuffer('a string'); // false
Buffer.isBuffer([]); // false
Buffer.isBuffer(new Uint8Array(1024)); // false
const { Buffer } = require('node:buffer');
Buffer.isBuffer(Buffer.alloc(10)); // true
Buffer.isBuffer(Buffer.from('foo')); // true
Buffer.isBuffer('a string'); // false
Buffer.isBuffer([]); // false
Buffer.isBuffer(new Uint8Array(1024)); // false
Static method: Buffer.isEncoding(encoding)
#
Returns true
if encoding
is the name of a supported character encoding,
or false
otherwise.
import { Buffer } from 'node:buffer';
console.log(Buffer.isEncoding('utf8'));
// Prints: true
console.log(Buffer.isEncoding('hex'));
// Prints: true
console.log(Buffer.isEncoding('utf/8'));
// Prints: false
console.log(Buffer.isEncoding(''));
// Prints: false
const { Buffer } = require('node:buffer');
console.log(Buffer.isEncoding('utf8'));
// Prints: true
console.log(Buffer.isEncoding('hex'));
// Prints: true
console.log(Buffer.isEncoding('utf/8'));
// Prints: false
console.log(Buffer.isEncoding(''));
// Prints: false
Class property: Buffer.poolSize
#
- <integer> Default:
8192
This is the size (in bytes) of pre-allocated internal Buffer
instances used
for pooling. This value may be modified.
buf[index]
#
index
<integer>
The index operator [index]
can be used to get and set the octet at position
index
in buf
. The values refer to individual bytes, so the legal value
range is between 0x00
and 0xFF
(hex) or 0
and 255
(decimal).
This operator is inherited from Uint8Array
, so its behavior on out-of-bounds
access is the same as Uint8Array
. In other words, buf[index]
returns
undefined
when index
is negative or greater or equal to buf.length
, and
buf[index] = value
does not modify the buffer if index
is negative or
>= buf.length
.
import { Buffer } from 'node:buffer';
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('utf8'));
// Prints: Node.js
const { Buffer } = require('node:buffer');
// Copy an ASCII string into a `Buffer` one byte at a time.
// (This only works for ASCII-only strings. In general, one should use
// `Buffer.from()` to perform this conversion.)
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
console.log(buf.toString('utf8'));
// Prints: Node.js
buf.buffer
#
- <ArrayBuffer> The underlying
ArrayBuffer
object based on which thisBuffer
object is created.
This ArrayBuffer
is not guaranteed to correspond exactly to the original
Buffer
. See the notes on buf.byteOffset
for details.
import { Buffer } from 'node:buffer';
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
const { Buffer } = require('node:buffer');
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
buf.byteOffset
#
- <integer> The
byteOffset
of theBuffer
s underlyingArrayBuffer
object.
When setting byteOffset
in Buffer.from(ArrayBuffer, byteOffset, length)
,
or sometimes when allocating a Buffer
smaller than Buffer.poolSize
, the
buffer does not start from a zero offset on the underlying ArrayBuffer
.
This can cause problems when accessing the underlying ArrayBuffer
directly
using buf.buffer
, as other parts of the ArrayBuffer
may be unrelated
to the Buffer
object itself.
A common issue when creating a TypedArray
object that shares its memory with
a Buffer
is that in this case one needs to specify the byteOffset
correctly:
import { Buffer } from 'node:buffer';
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
const { Buffer } = require('node:buffer');
// Create a buffer smaller than `Buffer.poolSize`.
const nodeBuffer = Buffer.from([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
// When casting the Node.js Buffer to an Int8Array, use the byteOffset
// to refer only to the part of `nodeBuffer.buffer` that contains the memory
// for `nodeBuffer`.
new Int8Array(nodeBuffer.buffer, nodeBuffer.byteOffset, nodeBuffer.length);
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
with which to comparebuf
.targetStart
<integer> The offset withintarget
at which to begin comparison. Default:0
.targetEnd
<integer> The offset withintarget
at which to end comparison (not inclusive). Default:target.length
.sourceStart
<integer> The offset withinbuf
at which to begin comparison. Default:0
.sourceEnd
<integer> The offset withinbuf
at which to end comparison (not inclusive). Default:buf.length
.- Returns: <integer>
Compares buf
with target
and returns a number indicating whether buf
comes before, after, or is the same as target
in sort order.
Comparison is based on the actual sequence of bytes in each Buffer
.
0
is returned iftarget
is the same asbuf
1
is returned iftarget
should come beforebuf
when sorted.-1
is returned iftarget
should come afterbuf
when sorted.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
console.log(buf1.compare(buf1));
// Prints: 0
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: -1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: 1
console.log([buf1, buf2, buf3].sort(Buffer.compare));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2].)
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf
respectively.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: 0
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: -1
console.log(buf1.compare(buf2, 5, 6, 5));
// Prints: 1
ERR_OUT_OF_RANGE
is thrown if targetStart < 0
, sourceStart < 0
,
targetEnd > target.byteLength
, or sourceEnd > source.byteLength
.
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])
#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
to copy into.targetStart
<integer> The offset withintarget
at which to begin writing. Default:0
.sourceStart
<integer> The offset withinbuf
from which to begin copying. Default:0
.sourceEnd
<integer> The offset withinbuf
at which to stop copying (not inclusive). Default:buf.length
.- Returns: <integer> The number of bytes copied.
Copies data from a region of buf
to a region in target
, even if the target
memory region overlaps with buf
.
TypedArray.prototype.set()
performs the same operation, and is available
for all TypedArrays, including Node.js Buffer
s, although it takes
different function arguments.
import { Buffer } from 'node:buffer';
// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
const { Buffer } = require('node:buffer');
// Create two `Buffer` instances.
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
// Copy `buf1` bytes 16 through 19 into `buf2` starting at byte 8 of `buf2`.
buf1.copy(buf2, 8, 16, 20);
// This is equivalent to:
// buf2.set(buf1.subarray(16, 20), 8);
console.log(buf2.toString('ascii', 0, 25));
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
import { Buffer } from 'node:buffer';
// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
const { Buffer } = require('node:buffer');
// Create a `Buffer` and copy data from one region to an overlapping region
// within the same `Buffer`.
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
console.log(buf.toString());
// Prints: efghijghijklmnopqrstuvwxyz
buf.entries()
#
- Returns: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the contents
of buf
.
import { Buffer } from 'node:buffer';
// Log the entire contents of a `Buffer`.
const buf = Buffer.from('buffer');
for (const pair of buf.entries()) {
console.log(pair);
}
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
const { Buffer } = require('node:buffer');
// Log the entire contents of a `Buffer`.
const buf = Buffer.from('buffer');
for (const pair of buf.entries()) {
console.log(pair);
}
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
buf.equals(otherBuffer)
#
otherBuffer
<Buffer> | <Uint8Array> ABuffer
orUint8Array
with which to comparebuf
.- Returns: <boolean>
Returns true
if both buf
and otherBuffer
have exactly the same bytes,
false
otherwise. Equivalent to
buf.compare(otherBuffer) === 0
.
import { Buffer } from 'node:buffer';
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
const { Buffer } = require('node:buffer');
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
console.log(buf1.equals(buf2));
// Prints: true
console.log(buf1.equals(buf3));
// Prints: false
buf.fill(value[, offset[, end]][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> The value with which to fillbuf
. Empty value (string, Uint8Array, Buffer) is coerced to0
.offset
<integer> Number of bytes to skip before starting to fillbuf
. Default:0
.end
<integer> Where to stop fillingbuf
(not inclusive). Default:buf.length
.encoding
<string> The encoding forvalue
ifvalue
is a string. Default:'utf8'
.- Returns: <Buffer> A reference to
buf
.
Fills buf
with the specified value
. If the offset
and end
are not given,
the entire buf
will be filled:
import { Buffer } from 'node:buffer';
// Fill a `Buffer` with the ASCII character 'h'.
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
// Fill a buffer with empty string
const c = Buffer.allocUnsafe(5).fill('');
console.log(c.fill(''));
// Prints: <Buffer 00 00 00 00 00>
const { Buffer } = require('node:buffer');
// Fill a `Buffer` with the ASCII character 'h'.
const b = Buffer.allocUnsafe(50).fill('h');
console.log(b.toString());
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
// Fill a buffer with empty string
const c = Buffer.allocUnsafe(5).fill('');
console.log(c.fill(''));
// Prints: <Buffer 00 00 00 00 00>
value
is coerced to a uint32
value if it is not a string, Buffer
, or
integer. If the resulting integer is greater than 255
(decimal), buf
will be
filled with value & 255
.
If the final write of a fill()
operation falls on a multi-byte character,
then only the bytes of that character that fit into buf
are written:
import { Buffer } from 'node:buffer';
// Fill a `Buffer` with character that takes up two bytes in UTF-8.
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
const { Buffer } = require('node:buffer');
// Fill a `Buffer` with character that takes up two bytes in UTF-8.
console.log(Buffer.allocUnsafe(5).fill('\u0222'));
// Prints: <Buffer c8 a2 c8 a2 c8>
If value
contains invalid characters, it is truncated; if no valid
fill data remains, an exception is thrown:
import { Buffer } from 'node:buffer';
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
const { Buffer } = require('node:buffer');
const buf = Buffer.allocUnsafe(5);
console.log(buf.fill('a'));
// Prints: <Buffer 61 61 61 61 61>
console.log(buf.fill('aazz', 'hex'));
// Prints: <Buffer aa aa aa aa aa>
console.log(buf.fill('zz', 'hex'));
// Throws an exception.
buf.includes(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. Default:0
.encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
.- Returns: <boolean>
true
ifvalue
was found inbuf
,false
otherwise.
Equivalent to buf.indexOf() !== -1
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this is a buffer');
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this is a buffer');
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
console.log(buf.includes(97));
// Prints: true (97 is the decimal ASCII value for 'a')
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: true
console.log(buf.includes('this', 4));
// Prints: false
buf.indexOf(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. Default:0
.encoding
<string> Ifvalue
is a string, this is the encoding used to determine the binary representation of the string that will be searched for inbuf
. Default:'utf8'
.- Returns: <integer> The index of the first occurrence of
value
inbuf
, or-1
ifbuf
does not containvalue
.
If value
is:
- a string,
value
is interpreted according to the character encoding inencoding
. - a
Buffer
orUint8Array
,value
will be used in its entirety. To compare a partialBuffer
, usebuf.subarray
. - a number,
value
will be interpreted as an unsigned 8-bit integer value between0
and255
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this is a buffer');
console.log(buf.indexOf('this'));
// Prints: 0
console.log(buf.indexOf('is'));
// Prints: 2
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
console.log(buf.indexOf(97));
// Prints: 8 (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
// Prints: 8
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.indexOf('\u03a3', 0, 'utf16le'));
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', -4, 'utf16le'));
// Prints: 6
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. If the result
of coercion is NaN
or 0
, then the entire buffer will be searched. This
behavior matches String.prototype.indexOf()
.
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0.
// Prints: 1, searching the whole buffer.
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
If value
is an empty string or empty Buffer
and byteOffset
is less
than buf.length
, byteOffset
will be returned. If value
is empty and
byteOffset
is at least buf.length
, buf.length
will be returned.
buf.keys()
#
- Returns: <Iterator>
Creates and returns an iterator of buf
keys (indices).
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
for (const key of buf.keys()) {
console.log(key);
}
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
for (const key of buf.keys()) {
console.log(key);
}
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
buf.lastIndexOf(value[, byteOffset][, encoding])
#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search for.byteOffset
<integer> Where to begin searching inbuf
. If negative, then offset is calculated from the end ofbuf
. Default:buf.length - 1
.encoding
<string> Ifvalue
is a string, this is the encoding used to determine the binary representation of the string that will be searched for inbuf
. Default:'utf8'
.- Returns: <integer> The index of the last occurrence of
value
inbuf
, or-1
ifbuf
does not containvalue
.
Identical to buf.indexOf()
, except the last occurrence of value
is found
rather than the first occurrence.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
const { Buffer } = require('node:buffer');
const buf = Buffer.from('this buffer is a buffer');
console.log(buf.lastIndexOf('this'));
// Prints: 0
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 17
console.log(buf.lastIndexOf(97));
// Prints: 15 (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 5));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 4));
// Prints: -1
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'utf16le');
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'utf16le'));
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'utf16le'));
// Prints: 4
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
, like {}
or undefined
, will search the whole buffer.
This behavior matches String.prototype.lastIndexOf()
.
import { Buffer } from 'node:buffer';
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
const { Buffer } = require('node:buffer');
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte.
// Prints: 2, equivalent to searching for 99 or 'c'.
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN.
// Prints: 1, searching the whole buffer.
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0.
// Prints: -1, equivalent to passing 0.
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
If value
is an empty string or empty Buffer
, byteOffset
will be returned.
buf.length
#
Returns the number of bytes in buf
.
import { Buffer } from 'node:buffer';
// Create a `Buffer` and write a shorter string to it using UTF-8.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'utf8');
console.log(buf.length);
// Prints: 1234
const { Buffer } = require('node:buffer');
// Create a `Buffer` and write a shorter string to it using UTF-8.
const buf = Buffer.alloc(1234);
console.log(buf.length);
// Prints: 1234
buf.write('some string', 0, 'utf8');
console.log(buf.length);
// Prints: 1234
buf.parent
#
buf.buffer
instead.The buf.parent
property is a deprecated alias for buf.buffer
.
buf.readBigInt64BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads a signed, big-endian 64-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed
values.
buf.readBigInt64LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads a signed, little-endian 64-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed
values.
buf.readBigUInt64BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads an unsigned, big-endian 64-bit integer from buf
at the specified
offset
.
This function is also available under the readBigUint64BE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64BE(0));
// Prints: 4294967295n
buf.readBigUInt64LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy:0 <= offset <= buf.length - 8
. Default:0
.- Returns: <bigint>
Reads an unsigned, little-endian 64-bit integer from buf
at the specified
offset
.
This function is also available under the readBigUint64LE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff]);
console.log(buf.readBigUInt64LE(0));
// Prints: 18446744069414584320n
buf.readDoubleBE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <number>
Reads a 64-bit, big-endian double from buf
at the specified offset
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleBE(0));
// Prints: 8.20788039913184e-304
buf.readDoubleLE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 8
. Default:0
.- Returns: <number>
Reads a 64-bit, little-endian double from buf
at the specified offset
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
console.log(buf.readDoubleLE(0));
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readFloatBE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <number>
Reads a 32-bit, big-endian float from buf
at the specified offset
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatBE(0));
// Prints: 2.387939260590663e-38
buf.readFloatLE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <number>
Reads a 32-bit, little-endian float from buf
at the specified offset
.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, 2, 3, 4]);
console.log(buf.readFloatLE(0));
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readInt8([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
Reads a signed 8-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([-1, 5]);
console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([-1, 5]);
console.log(buf.readInt8(0));
// Prints: -1
console.log(buf.readInt8(1));
// Prints: 5
console.log(buf.readInt8(2));
// Throws ERR_OUT_OF_RANGE.
buf.readInt16BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads a signed, big-endian 16-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16BE(0));
// Prints: 5
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16BE(0));
// Prints: 5
buf.readInt16LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads a signed, little-endian 16-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 5]);
console.log(buf.readInt16LE(0));
// Prints: 1280
console.log(buf.readInt16LE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readInt32BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads a signed, big-endian 32-bit integer from buf
at the specified offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32BE(0));
// Prints: 5
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32BE(0));
// Prints: 5
buf.readInt32LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads a signed, little-endian 32-bit integer from buf
at the specified
offset
.
Integers read from a Buffer
are interpreted as two's complement signed values.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0, 0, 0, 5]);
console.log(buf.readInt32LE(0));
// Prints: 83886080
console.log(buf.readInt32LE(1));
// Throws ERR_OUT_OF_RANGE.
buf.readIntBE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a big-endian, two's complement signed value
supporting up to 48 bits of accuracy.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
console.log(buf.readIntBE(1, 0).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readIntLE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a little-endian, two's complement signed value
supporting up to 48 bits of accuracy.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: -546f87a9cbee
buf.readUInt8([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 1
. Default:0
.- Returns: <integer>
Reads an unsigned 8-bit integer from buf
at the specified offset
.
This function is also available under the readUint8
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([1, -2]);
console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([1, -2]);
console.log(buf.readUInt8(0));
// Prints: 1
console.log(buf.readUInt8(1));
// Prints: 254
console.log(buf.readUInt8(2));
// Throws ERR_OUT_OF_RANGE.
buf.readUInt16BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads an unsigned, big-endian 16-bit integer from buf
at the specified
offset
.
This function is also available under the readUint16BE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 1234
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 3456
buf.readUInt16LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 2
. Default:0
.- Returns: <integer>
Reads an unsigned, little-endian 16-bit integer from buf
at the specified
offset
.
This function is also available under the readUint16LE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56]);
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(2).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUInt32BE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads an unsigned, big-endian 32-bit integer from buf
at the specified
offset
.
This function is also available under the readUint32BE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 12345678
buf.readUInt32LE([offset])
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - 4
. Default:0
.- Returns: <integer>
Reads an unsigned, little-endian 32-bit integer from buf
at the specified
offset
.
This function is also available under the readUint32LE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
console.log(buf.readUInt32LE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(1).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUIntBE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned big-endian integer supporting
up to 48 bits of accuracy.
This function is also available under the readUintBE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readUIntBE(1, 6).toString(16));
// Throws ERR_OUT_OF_RANGE.
buf.readUIntLE(offset, byteLength)
#
offset
<integer> Number of bytes to skip before starting to read. Must satisfy0 <= offset <= buf.length - byteLength
.byteLength
<integer> Number of bytes to read. Must satisfy0 < byteLength <= 6
.- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned, little-endian integer supporting
up to 48 bits of accuracy.
This function is also available under the readUintLE
alias.
import { Buffer } from 'node:buffer';
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
const { Buffer } = require('node:buffer');
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
console.log(buf.readUIntLE(0, 6).toString(16));
// Prints: ab9078563412
buf.subarray([start[, end]])
#
start
<integer> Where the newBuffer
will start. Default:0
.end
<integer> Where the newBuffer
will end (not inclusive). Default:buf.length
.- Returns: <Buffer>
Returns a new Buffer
that references the same memory as the original, but
offset and cropped by the start
and end
indices.
Specifying end
greater than buf.length
will return the same result as
that of end
equal to buf.length
.
This method is inherited from TypedArray.prototype.subarray()
.
Modifying the new Buffer
slice will modify the memory in the original Buffer
because the allocated memory of the two objects overlap.
import { Buffer } from 'node:buffer';
// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
const { Buffer } = require('node:buffer');
// Create a `Buffer` with the ASCII alphabet, take a slice, and modify one byte
// from the original `Buffer`.
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'.
buf1[i] = i + 97;
}
const buf2 = buf1.subarray(0, 3);
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: abc
buf1[0] = 33;
console.log(buf2.toString('ascii', 0, buf2.length));
// Prints: !bc
Specifying negative indexes causes the slice to be generated relative to the
end of buf
rather than the beginning.
import { Buffer } from 'node:buffer';
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)
console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)
console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
const { Buffer } = require('node:buffer');
const buf = Buffer.from('buffer');
console.log(buf.subarray(-6, -1).toString());
// Prints: buffe
// (Equivalent to buf.subarray(0, 5).)
console.log(buf.subarray(-6, -2).toString());
// Prints: buff
// (Equivalent to buf.subarray(0, 4).)
console.log(buf.subarray(-5, -2).toString());
// Prints: uff
// (Equivalent to buf.subarray(1, 4).)
buf.slice([start[, end]])
#
start
<integer> Where the newBuffer
will start. Default:0
.end
<integer> Where the newBuffer
will end (not inclusive). Default:buf.length
.- Returns: <Buffer>
buf.subarray