- Assertion Testing
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- C/C++ Addons - N-API
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- Command Line Options
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- DNS
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- Globals
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- HTTP/2
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- Process
- Punycode
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- Readline
- REPL
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- String Decoder
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- Trace Events
- TTY
- UDP/Datagram
- URL
- Utilities
- V8
- VM
- Worker Threads
- Zlib
Node.js v10.18.1-test20200102a1b095dd46 Documentation
Table of Contents
-
- util.callbackify(original)
- util.debuglog(section)
- util.deprecate(fn, msg[, code])
- util.format(format[, ...args])
- util.formatWithOptions(inspectOptions, format[, ...args])
- util.getSystemErrorName(err)
- util.inherits(constructor, superConstructor)
- util.inspect(object[, options])
- util.isDeepStrictEqual(val1, val2)
-
- util.types.isAnyArrayBuffer(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.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.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)
-
- util._extend(target, source)
- util.debug(string)
- util.error([...strings])
- 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)
- util.print([...strings])
- util.puts([...strings])
Util#
The util
module is primarily designed to support the needs of Node.js' own
internal APIs. However, many of the utilities are useful for application and
module developers as well. It can be accessed using:
const util = require('util');
util.callbackify(original)[src]#
original
<Function> Anasync
function- Returns: <Function> a callback style function
Takes an async
function (or a function that returns a Promise
) and returns a
function following the error-first callback style, i.e. taking
an (err, value) => ...
callback as the last argument. In the callback, the
first argument will be the rejection reason (or null
if the Promise
resolved), and the second argument will be the resolved value.
const util = require('util');
async function fn() {
return 'hello world';
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
if (err) throw err;
console.log(ret);
});
Will print:
hello world
The callback is executed asynchronously, and will have a limited stack trace.
If the callback throws, the process will emit an 'uncaughtException'
event, and if not handled will exit.
Since null
has a special meaning as the first argument to a callback, if a
wrapped function rejects a Promise
with a falsy value as a reason, the value
is wrapped in an Error
with the original value stored in a field named
reason
.
function fn() {
return Promise.reject(null);
}
const callbackFunction = util.callbackify(fn);
callbackFunction((err, ret) => {
// When the Promise was rejected with `null` it is wrapped with an Error and
// the original value is stored in `reason`.
err && err.hasOwnProperty('reason') && err.reason === null; // true
});
util.debuglog(section)[src]#
section
<string> A string identifying the portion of the application for which thedebuglog
function is being created.- Returns: <Function> The logging function
The util.debuglog()
method is used to create a function that conditionally
writes debug messages to stderr
based on the existence of the NODE_DEBUG
environment variable. If the section
name appears within the value of that
environment variable, then the returned function operates similar to
console.error()
. If not, then the returned function is a no-op.
const util = require('util');
const debuglog = util.debuglog('foo');
debuglog('hello from foo [%d]', 123);
If this program is run with NODE_DEBUG=foo
in the environment, then
it will output something like:
FOO 3245: hello from foo [123]
where 3245
is the process id. If it is not run with that
environment variable set, then it will not print anything.
The section
supports wildcard also:
const util = require('util');
const debuglog = util.debuglog('foo-bar');
debuglog('hi there, it\'s foo-bar [%d]', 2333);
if it is run with NODE_DEBUG=foo*
in the environment, then it will output
something like:
FOO-BAR 3257: hi there, it's foo-bar [2333]
Multiple comma-separated section
names may be specified in the NODE_DEBUG
environment variable: NODE_DEBUG=fs,net,tls
.
util.deprecate(fn, msg[, code])#
fn
<Function> The function that is being deprecated.msg
<string> A warning message to display when the deprecated function is invoked.code
<string> A deprecation code. See the list of deprecated APIs for a list of codes.- Returns: <Function> The deprecated function wrapped to emit a warning.
The util.deprecate()
method wraps fn
(which may be a function or class) in
such a way that it is marked as deprecated.
const util = require('util');
exports.obsoleteFunction = util.deprecate(() => {
// Do something here.
}, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.');
When called, util.deprecate()
will return a function that will emit a
DeprecationWarning
using the 'warning'
event. The warning will
be emitted and printed to stderr
the first time the returned function is
called. After the warning is emitted, the wrapped function is called without
emitting a warning.
If the same optional code
is supplied in multiple calls to util.deprecate()
,
the warning will be emitted only once for that code
.
const util = require('util');
const fn1 = util.deprecate(someFunction, someMessage, 'DEP0001');
const fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001');
fn1(); // emits a deprecation warning with code DEP0001
fn2(); // does not emit a deprecation warning because it has the same code
If either the --no-deprecation
or --no-warnings
command line flags are
used, or if the process.noDeprecation
property is set to true
prior to
the first deprecation warning, the util.deprecate()
method does nothing.
If the --trace-deprecation
or --trace-warnings
command line flags are set,
or the process.traceDeprecation
property is set to true
, a warning and a
stack trace are printed to stderr
the first time the deprecated function is
called.
If the --throw-deprecation
command line flag is set, or the
process.throwDeprecation
property is set to true
, then an exception will be
thrown when the deprecated function is called.
The --throw-deprecation
command line flag and process.throwDeprecation
property take precedence over --trace-deprecation
and
process.traceDeprecation
.
util.format(format[, ...args])[src]#
format
<string> Aprintf
-like format string.
The util.format()
method returns a formatted string using the first argument
as a printf
-like format.
The first argument is a string containing zero or more placeholder tokens. Each placeholder token is replaced with the converted value from the corresponding argument. Supported placeholders are:
%s
-String
.%d
-Number
(integer or floating point value) orBigInt
.%i
- Integer orBigInt
.%f
- Floating point value.%j
- JSON. Replaced with the string'[Circular]'
if the argument contains circular references.%o
-Object
. A string representation of an object with generic JavaScript object formatting. Similar toutil.inspect()
with options{ showHidden: true, showProxy: true }
. This will show the full object including non-enumerable properties and proxies.%O
-Object
. A string representation of an object with generic JavaScript object formatting. Similar toutil.inspect()
without options. This will show the full object not including non-enumerable properties and proxies.%%
- single percent sign ('%'
). This does not consume an argument.- Returns: <string> The formatted string
If the placeholder does not have a corresponding argument, the placeholder is not replaced.
util.format('%s:%s', 'foo');
// Returns: 'foo:%s'
If there are more arguments passed to the util.format()
method than the number
of placeholders, the extra arguments are coerced into strings then concatenated
to the returned string, each delimited by a space. Excessive arguments whose
typeof
is 'object'
or 'symbol'
(except null
) will be transformed by
util.inspect()
.
util.format('%s:%s', 'foo', 'bar', 'baz'); // 'foo:bar baz'
If the first argument is not a string then util.format()
returns
a string that is the concatenation of all arguments separated by spaces.
Each argument is converted to a string using util.inspect()
.
util.format(1, 2, 3); // '1 2 3'
If only one argument is passed to util.format()
, it is returned as it is
without any formatting.
util.format('%% %s'); // '%% %s'
Please note that util.format()
is a synchronous method that is mainly
intended as a debugging tool. Some input values can have a significant
performance overhead that can block the event loop. Use this function
with care and never in a hot code path.
util.formatWithOptions(inspectOptions, format[, ...args])[src]#
This function is identical to util.format()
, except in that it takes
an inspectOptions
argument which specifies options that are passed along to
util.inspect()
.
util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 });
// Returns 'See object { foo: 42 }', where `42` is colored as a number
// when printed to a terminal.
util.getSystemErrorName(err)[src]#
Returns the string name for a numeric error code that comes from a Node.js API. The mapping between error codes and error names is platform-dependent. See Common System Errors for the names of common errors.
fs.access('file/that/does/not/exist', (err) => {
const name = util.getSystemErrorName(err.errno);
console.error(name); // ENOENT
});
util.inherits(constructor, superConstructor)[src]#
constructor
<Function>superConstructor
<Function>
Usage of util.inherits()
is discouraged. Please use the ES6 class
and
extends
keywords to get language level inheritance support. Also note
that the two styles are semantically incompatible.
Inherit the prototype methods from one constructor into another. The
prototype of constructor
will be set to a new object created from
superConstructor
.
As an additional convenience, superConstructor
will be accessible
through the constructor.super_
property.
const util = require('util');
const EventEmitter = require('events');
function MyStream() {
EventEmitter.call(this);
}
util.inherits(MyStream, EventEmitter);
MyStream.prototype.write = function(data) {
this.emit('data', data);
};
const stream = new MyStream();
console.log(stream instanceof EventEmitter); // true
console.log(MyStream.super_ === EventEmitter); // true
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('It works!'); // Received data: "It works!"
ES6 example using class
and extends
:
const EventEmitter = require('events');
class MyStream extends EventEmitter {
write(data) {
this.emit('data', data);
}
}
const stream = new MyStream();
stream.on('data', (data) => {
console.log(`Received data: "${data}"`);
});
stream.write('With ES6');
util.inspect(object[, options])#
util.inspect(object[, showHidden[, depth[, colors]]])
object
<any> Any JavaScript primitive orObject
.-
options
<Object>showHidden
<boolean> Iftrue
, theobject
's non-enumerable symbols and properties will be included in the formatted result as well asWeakMap
andWeakSet
entries. Default:false
.depth
<number> Specifies the number of times to recurse while formatting theobject
. This is useful for inspecting large complicated objects. To make it recurse up to the maximum call stack size passInfinity
ornull
. Default:2
.colors
<boolean> Iftrue
, the output will be styled with ANSI color codes. Colors are customizable, see Customizingutil.inspect
colors. Default:false
.customInspect
<boolean> Iffalse
, then custominspect(depth, opts)
functions will not be called. Default:true
.showProxy
<boolean> Iftrue
, then objects and functions that areProxy
objects will be introspected to show theirtarget
andhandler
objects. Default:false
.maxArrayLength
<number> Specifies the maximum number ofArray
,TypedArray
,WeakMap
andWeakSet
elements to include when formatting. Set tonull
orInfinity
to show all elements. Set to0
or negative to show no elements. Default:100
.breakLength
<number> The length at which an object's keys are split across multiple lines. Set toInfinity
to format an object as a single line. Default:60
for legacy compatibility.compact
<boolean> Setting this tofalse
changes the default indentation to use a line break for each object key instead of lining up multiple properties in one line. It will also break text that is above thebreakLength
size into smaller and better readable chunks and indents objects the same as arrays. Note that no text will be reduced below 16 characters, no matter thebreakLength
size. For more information, see the example below. Default:true
.sorted
<boolean> | <Function> If set totrue
or a function, all properties of an object and Set and Map entries will be sorted in the returned string. If set totrue
the default sort is going to be used. If set to a function, it is used as a compare function.
- Returns: <string> The representation of passed object
The util.inspect()
method returns a string representation of object
that is
intended for debugging. The output of util.inspect
may change at any time
and should not be depended upon programmatically. Additional options
may be
passed that alter certain aspects of the formatted string.
util.inspect()
will use the constructor's name and/or @@toStringTag
to make
an identifiable tag for an inspected value.
class Foo {
get [Symbol.toStringTag]() {
return 'bar';
}
}
class Bar {}
const baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } });
util.inspect(new Foo()); // 'Foo [bar] {}'
util.inspect(new Bar()); // 'Bar {}'
util.inspect(baz); // '[foo] {}'
The following example inspects all properties of the util
object:
const util = require('util');
console.log(util.inspect(util, { showHidden: true, depth: null }));
Values may supply their own custom inspect(depth, opts)
functions, when
called these receive the current depth
in the recursive inspection, as well as
the options object passed to util.inspect()
.
The following example highlights the difference with the compact
option:
const util = require('util');
const o = {
a: [1, 2, [[
'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do ' +
'eiusmod tempor incididunt ut labore et dolore magna aliqua.',
'test',
'foo']], 4],
b: new Map([['za', 1], ['zb', 'test']])
};
console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 }));
// This will print
// { a:
// [ 1,
// 2,
// [ [ 'Lorem ipsum dolor sit amet, consectetur [...]', // A long line
// 'test',
// 'foo' ] ],
// 4 ],
// b: Map { 'za' => 1, 'zb' => 'test' } }
// Setting `compact` to false changes the output to be more reader friendly.
console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));
// {
// a: [
// 1,
// 2,
// [
// [
// 'Lorem ipsum dolor sit amet, consectetur ' +
// 'adipiscing elit, sed do eiusmod tempor ' +
// 'incididunt ut labore et dolore magna ' +
// 'aliqua.,
// 'test',
// 'foo'
// ]
// ],
// 4
// ],
// b: Map {
// 'za' => 1,
// 'zb' => 'test'
// }
// }
// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
// single line.
// Reducing the `breakLength` will split the "Lorem ipsum" text in smaller
// chunks.
Using the showHidden
option allows to inspect WeakMap
and WeakSet
entries. If there are more entries than maxArrayLength
, there is no guarantee
which entries are displayed. That means retrieving the same WeakSet
entries twice might actually result in a different output. Besides this any item
might be collected at any point of time by the garbage collector if there is no
strong reference left to that object. Therefore there is no guarantee to get a
reliable output.
const { inspect } = require('util');
const obj = { a: 1 };
const obj2 = { b: 2 };
const weakSet = new WeakSet([obj, obj2]);
console.log(inspect(weakSet, { showHidden: true }));
// WeakSet { { a: 1 }, { b: 2 } }
The sorted
option makes sure the output is identical, no matter of the
properties insertion order:
const { inspect } = require('util');
const assert = require('assert');
const o1 = {
b: [2, 3, 1],
a: '`a` comes before `b`',
c: new Set([2, 3, 1])
};
console.log(inspect(o1, { sorted: true }));
// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set { 1, 2, 3 } }
console.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) }));
// { c: Set { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }
const o2 = {
c: new Set([2, 1, 3]),
a: '`a` comes before `b`',
b: [2, 3, 1]
};
assert.strict.equal(
inspect(o1, { sorted: true }),
inspect(o2, { sorted: true })
);
Please note that util.inspect()
is a synchronous method that is mainly
intended as a debugging tool. Some input values can have a significant
performance overhead that can block the event loop. Use this function
with care and never in a hot code path.
Customizing util.inspect
colors#
Color output (if enabled) of util.inspect
is customizable globally
via the util.inspect.styles
and util.inspect.colors
properties.
util.inspect.styles
is a map associating a style name to a color from
util.inspect.colors
.
The default styles and associated colors are:
number
-yellow
boolean
-yellow
string
-green
date
-magenta
regexp
-red
null
-bold
undefined
-grey
special
-cyan
(only applied to functions at this time)name
- (no styling)
The predefined color codes are: white
, grey
, black
, blue
, cyan
,
green
, magenta
, red
and yellow
. There are also bold
, italic
,
underline
and inverse
codes.
Color styling uses ANSI control codes that may not be supported on all terminals.
Custom inspection functions on Objects#
Objects may also define their own
[util.inspect.custom](depth, opts)
(or the equivalent
but deprecated inspect(depth, opts)
) function, which util.inspect()
will
invoke and use the result of when inspecting the object:
const util = require('util');
class Box {
constructor(value) {
this.value = value;
}
[util.inspect.custom](depth, options) {
if (depth < 0) {
return options.stylize('[Box]', 'special');
}
const newOptions = Object.assign({}, options, {
depth: options.depth === null ? null : options.depth - 1
});
// Five space padding because that's the size of "Box< ".
const padding = ' '.repeat(5);
const inner = util.inspect(this.value, newOptions)
.replace(/\n/g, `\n${padding}`);
return `${options.stylize('Box', 'special')}< ${inner} >`;
}
}
const box = new Box(true);
util.inspect(box);
// Returns: "Box< true >"
Custom [util.inspect.custom](depth, opts)
functions typically return a string
but may return a value of any type that will be formatted accordingly by
util.inspect()
.
const util = require('util');
const obj = { foo: 'this will not show up in the inspect() output' };
obj[util.inspect.custom] = (depth) => {
return { bar: 'baz' };
};
util.inspect(obj);
// Returns: "{ bar: 'baz' }"
util.inspect.custom#
- <symbol> that can be used to declare custom inspect functions.
In addition to being accessible through util.inspect.custom
, this
symbol is registered globally and can be
accessed in any environment as Symbol.for('nodejs.util.inspect.custom')
.
const inspect = Symbol.for('nodejs.util.inspect.custom');
class Password {
constructor(value) {
this.value = value;
}
toString() {
return 'xxxxxxxx';
}
[inspect]() {
return `Password <${this.toString()}>`;
}
}
const password = new Password('r0sebud');
console.log(password);
// Prints Password <xxxxxxxx>
See Custom inspection functions on Objects for more details.
util.inspect.defaultOptions#
The defaultOptions
value allows customization of the default options used by
util.inspect
. This is useful for functions like console.log
or
util.format
which implicitly call into util.inspect
. It shall be set to an
object containing one or more valid util.inspect()
options. Setting
option properties directly is also supported.
const util = require('util');
const arr = Array(101).fill(0);
console.log(arr); // logs the truncated array
util.inspect.defaultOptions.maxArrayLength = null;
console.log(arr); // logs the full array
util.isDeepStrictEqual(val1, val2)#
Returns true
if there is deep strict equality between val1
and val2
.
Otherwise, returns false
.
See assert.deepStrictEqual()
for more information about deep strict
equality.
util.promisify(original)#
original
<Function>- Returns: <Function>
Takes a function following the common error-first callback style, i.e. taking
an (err, value) => ...
callback as the last argument, and returns a version
that returns promises.
const util = require('util');
const fs = require('fs');
const stat = util.promisify(fs.stat);
stat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});
Or, equivalently using async function
s:
const util = require('util');
const fs = require('fs');
const stat = util.promisify(fs.stat);
async function callStat() {
const stats = await stat('.');
console.log(`This directory is owned by ${stats.uid}`);
}
If there is an original[util.promisify.custom]
property present, promisify
will return its value, see Custom promisified functions.
promisify()
assumes that original
is a function taking a callback as its
final argument in all cases. If original
is not a function, promisify()
will throw an error. If original
is a function but its last argument is not
an error-first callback, it will still be passed an error-first
callback as its last argument.
Custom promisified functions#
Using the util.promisify.custom
symbol one can override the return value of
util.promisify()
:
const util = require('util');
function doSomething(foo, callback) {
// ...
}
doSomething[util.promisify.custom] = (foo) => {
return getPromiseSomehow();
};
const promisified = util.promisify(doSomething);
console.log(promisified === doSomething[util.promisify.custom]);
// prints 'true'
This can be useful for cases where the original function does not follow the standard format of taking an error-first callback as the last argument.
For example, with a function that takes in
(foo, onSuccessCallback, onErrorCallback)
:
doSomething[util.promisify.custom] = (foo) => {
return new Promise((resolve, reject) => {
doSomething(foo, resolve, reject);
});
};
If promisify.custom
is defined but is not a function, promisify()
will
throw an error.
util.promisify.custom#
A <symbol> that can be used to declare custom promisified variants of functions, see Custom promisified functions.
Class: util.TextDecoder#
An implementation of the WHATWG Encoding Standard TextDecoder
API.
const decoder = new TextDecoder('shift_jis');
let string = '';
let buffer;
while (buffer = getNextChunkSomehow()) {
string += decoder.decode(buffer, { stream: true });
}
string += decoder.decode(); // end-of-stream
WHATWG Supported Encodings#
Per the WHATWG Encoding Standard, the encodings supported by the
TextDecoder
API are outlined in the tables below. For each encoding,
one or more aliases may be used.
Different Node.js build configurations support different sets of encodings. While a very basic set of encodings is supported even on Node.js builds without ICU enabled, support for some encodings is provided only when Node.js is built with ICU and using the full ICU data (see Internationalization).
Encodings Supported Without ICU#
Encoding | Aliases |
---|---|
'utf-8' | 'unicode-1-1-utf-8' , 'utf8' |
'utf-16le' | 'utf-16' |
Encodings Supported by Default (With ICU)#
Encoding | Aliases |
---|---|
'utf-8' | 'unicode-1-1-utf-8' , 'utf8' |
'utf-16le' | 'utf-16' |
'utf-16be' |
Encodings Requiring Full ICU Data#
Encoding | Aliases |
---|---|
'ibm866' | '866' , 'cp866' , 'csibm866' |
'iso-8859-2' | 'csisolatin2' , 'iso-ir-101' , 'iso8859-2' , 'iso88592' , 'iso_8859-2' , 'iso_8859-2:1987' , 'l2' , 'latin2' |
'iso-8859-3' | 'csisolatin3' , 'iso-ir-109' , 'iso8859-3' , 'iso88593' , 'iso_8859-3' , 'iso_8859-3:1988' , 'l3' , 'latin3' |
'iso-8859-4' | 'csisolatin4' , 'iso-ir-110' , 'iso8859-4' , 'iso88594' , 'iso_8859-4' , 'iso_8859-4:1988' , 'l4' , 'latin4' |
'iso-8859-5' | 'csisolatincyrillic' , 'cyrillic' , 'iso-ir-144' , 'iso8859-5' , 'iso88595' , 'iso_8859-5' , 'iso_8859-5:1988' |
'iso-8859-6' | 'arabic' , 'asmo-708' , 'csiso88596e' , 'csiso88596i' , 'csisolatinarabic' , 'ecma-114' , 'iso-8859-6-e' , 'iso-8859-6-i' , 'iso-ir-127' , 'iso8859-6' , 'iso88596' , 'iso_8859-6' , 'iso_8859-6:1987' |
'iso-8859-7' | 'csisolatingreek' , 'ecma-118' , 'elot_928' , 'greek' , 'greek8' , 'iso-ir-126' , 'iso8859-7' , 'iso88597' , 'iso_8859-7' , 'iso_8859-7:1987' , 'sun_eu_greek' |
'iso-8859-8' | 'csiso88598e' , 'csisolatinhebrew' , 'hebrew' , 'iso-8859-8-e' , 'iso-ir-138' , 'iso8859-8' , 'iso88598' , 'iso_8859-8' , 'iso_8859-8:1988' , 'visual' |
'iso-8859-8-i' | 'csiso88598i' , 'logical' |
'iso-8859-10' | 'csisolatin6' , 'iso-ir-157' , 'iso8859-10' , 'iso885910' , 'l6' , 'latin6' |
'iso-8859-13' | 'iso8859-13' , 'iso885913' |
'iso-8859-14' | 'iso8859-14' , 'iso885914' |
'iso-8859-15' | 'csisolatin9' , 'iso8859-15' , 'iso885915' , 'iso_8859-15' , 'l9' |
'koi8-r' | 'cskoi8r' , 'koi' , 'koi8' , 'koi8_r' |
'koi8-u' | 'koi8-ru' |
'macintosh' | 'csmacintosh' , 'mac' , 'x-mac-roman' |
'windows-874' | 'dos-874' , 'iso-8859-11' , 'iso8859-11' , 'iso885911' , 'tis-620' |
'windows-1250' | 'cp1250' , 'x-cp1250' |
'windows-1251' | 'cp1251' , 'x-cp1251' |
'windows-1252' | 'ansi_x3.4-1968' , 'ascii' , 'cp1252' , 'cp819' , 'csisolatin1' , 'ibm819' , 'iso-8859-1' , 'iso-ir-100' , 'iso8859-1' , 'iso88591' , 'iso_8859-1' , 'iso_8859-1:1987' , 'l1' , 'latin1' , 'us-ascii' , 'x-cp1252' |
'windows-1253' | 'cp1253' , 'x-cp1253' |
'windows-1254' | 'cp1254' , 'csisolatin5' , 'iso-8859-9' , 'iso-ir-148' , 'iso8859-9' , 'iso88599' , 'iso_8859-9' , 'iso_8859-9:1989' , 'l5' , 'latin5' , 'x-cp1254' |
'windows-1255' | 'cp1255' , 'x-cp1255' |
'windows-1256' | 'cp1256' , 'x-cp1256' |
'windows-1257' | 'cp1257' , 'x-cp1257' |
'windows-1258' | 'cp1258' , 'x-cp1258' |
'x-mac-cyrillic' | 'x-mac-ukrainian' |
'gbk' | 'chinese' , 'csgb2312' , 'csiso58gb231280' , 'gb2312' , 'gb_2312' , 'gb_2312-80' , 'iso-ir-58' , 'x-gbk' |
'gb18030' | |
'big5' | 'big5-hkscs' , 'cn-big5' , 'csbig5' , 'x-x-big5' |
'euc-jp' | 'cseucpkdfmtjapanese' , 'x-euc-jp' |
'iso-2022-jp' | 'csiso2022jp' |
'shift_jis' | 'csshiftjis' , 'ms932' , 'ms_kanji' , 'shift-jis' , 'sjis' , 'windows-31j' , 'x-sjis' |
'euc-kr' | 'cseuckr' , 'csksc56011987' , 'iso-ir-149' , 'korean' , 'ks_c_5601-1987' , 'ks_c_5601-1989' , 'ksc5601' , 'ksc_5601' , 'windows-949' |
The 'iso-8859-16'
encoding listed in the WHATWG Encoding Standard
is not supported.
new TextDecoder([encoding[, options]])#
encoding
<string> Identifies theencoding
that thisTextDecoder
instance supports. Default:'utf-8'
.-
options
<Object>fatal
<boolean>true
if decoding failures are fatal. This option is only supported when ICU is enabled (see Internationalization). Default:false
.ignoreBOM
<boolean> Whentrue
, theTextDecoder
will include the byte order mark in the decoded result. Whenfalse
, the byte order mark will be removed from the output. This option is only used whenencoding
is'utf-8'
,'utf-16be'
or'utf-16le'
. Default:false
.
Creates an new TextDecoder
instance. The encoding
may specify one of the
supported encodings or an alias.
textDecoder.decode([input[, options]])#
input
<ArrayBuffer> | <DataView> | <TypedArray> AnArrayBuffer
,DataView
orTyped Array
instance containing the encoded data.-
options
<Object>stream
<boolean>true
if additional chunks of data are expected. Default:false
.
- Returns: <string>
Decodes the input
and returns a string. If options.stream
is true
, any
incomplete byte sequences occurring at the end of the input
are buffered
internally and emitted after the next call to textDecoder.decode()
.
If textDecoder.fatal
is true
, decoding errors that occur will result in a
TypeError
being thrown.
textDecoder.encoding#
The encoding supported by the TextDecoder
instance.
textDecoder.fatal#
The value will be true
if decoding errors result in a TypeError
being
thrown.
textDecoder.ignoreBOM#
The value will be true
if the decoding result will include the byte order
mark.
Class: util.TextEncoder#
An implementation of the WHATWG Encoding Standard TextEncoder
API. All
instances of TextEncoder
only support UTF-8 encoding.
const encoder = new TextEncoder();
const uint8array = encoder.encode('this is some data');
textEncoder.encode([input])#
input
<string> The text to encode. Default: an empty string.- Returns: <Uint8Array>
UTF-8 encodes the input
string and returns a Uint8Array
containing the
encoded bytes.
textEncoder.encoding#
The encoding supported by the TextEncoder
instance. Always set to 'utf-8'
.
util.types#
util.types
provides a number of type checks for different kinds of built-in
objects. Unlike instanceof
or Object.prototype.toString.call(value)
,
these checks do not inspect properties of the object that are accessible from
JavaScript (like their prototype), and usually have the overhead of
calling into C++.
The result generally does not make any guarantees about what kinds of properties or behavior a value exposes in JavaScript. They are primarily useful for addon developers who prefer to do type checking in JavaScript.
util.types.isAnyArrayBuffer(value)#
Returns true
if the value is a built-in ArrayBuffer
or
SharedArrayBuffer
instance.
See also util.types.isArrayBuffer()
and
util.types.isSharedArrayBuffer()
.
util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true
util.types.isArgumentsObject(value)#
Returns true
if the value is an arguments
object.
function foo() {
util.types.isArgumentsObject(arguments); // Returns true
}
util.types.isArrayBuffer(value)#
Returns true
if the value is a built-in ArrayBuffer
instance.
This does not include SharedArrayBuffer
instances. Usually, it is
desirable to test for both; See util.types.isAnyArrayBuffer()
for that.
util.types.isArrayBuffer(new ArrayBuffer()); // Returns true
util.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false
util.types.isAsyncFunction(value)#
Returns true
if the value is an async function.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.
util.types.isAsyncFunction(function foo() {}); // Returns false
util.types.isAsyncFunction(async function foo() {}); // Returns true
util.types.isBigInt64Array(value)#
Returns true
if the value is a BigInt64Array
instance.
util.types.isBigInt64Array(new BigInt64Array()); // Returns true
util.types.isBigInt64Array(new BigUint64Array()); // Returns false
util.types.isBigUint64Array(value)#
Returns true
if the value is a BigUint64Array
instance.
util.types.isBigUint64Array(new BigInt64Array()); // Returns false
util.types.isBigUint64Array(new BigUint64Array()); // Returns true
util.types.isBooleanObject(value)#
Returns true
if the value is a boolean object, e.g. created
by new Boolean()
.
util.types.isBooleanObject(false); // Returns false
util.types.isBooleanObject(true); // Returns false
util.types.isBooleanObject(new Boolean(false)); // Returns true
util.types.isBooleanObject(new Boolean(true)); // Returns true
util.types.isBooleanObject(Boolean(false)); // Returns false
util.types.isBooleanObject(Boolean(true)); // Returns false
util.types.isBoxedPrimitive(value)#
Returns true
if the value is any boxed primitive object, e.g. created
by new Boolean()
, new String()
or Object(Symbol())
.
For example:
util.types.isBoxedPrimitive(false); // Returns false
util.types.isBoxedPrimitive(new Boolean(false)); // Returns true
util.types.isBoxedPrimitive(Symbol('foo')); // Returns false
util.types.isBoxedPrimitive(Object(Symbol('foo'))); // Returns true
util.types.isBoxedPrimitive(Object(BigInt(5))); // Returns true
util.types.isDataView(value)#
Returns true
if the value is a built-in DataView
instance.
const ab = new ArrayBuffer(20);
util.types.isDataView(new DataView(ab)); // Returns true
util.types.isDataView(new Float64Array()); // Returns false
See also ArrayBuffer.isView()
.
util.types.isDate(value)#
Returns true
if the value is a built-in Date
instance.
util.types.isDate(new Date()); // Returns true
util.types.isExternal(value)#
Returns true
if the value is a native External
value.
util.types.isFloat32Array(value)#
Returns true
if the value is a built-in Float32Array
instance.
util.types.isFloat32Array(new ArrayBuffer()); // Returns false
util.types.isFloat32Array(new Float32Array()); // Returns true
util.types.isFloat32Array(new Float64Array()); // Returns false
util.types.isFloat64Array(value)#
Returns true
if the value is a built-in Float64Array
instance.
util.types.isFloat64Array(new ArrayBuffer()); // Returns false
util.types.isFloat64Array(new Uint8Array()); // Returns false
util.types.isFloat64Array(new Float64Array()); // Returns true
util.types.isGeneratorFunction(value)#
Returns true
if the value is a generator function.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.
util.types.isGeneratorFunction(function foo() {}); // Returns false
util.types.isGeneratorFunction(function* foo() {}); // Returns true
util.types.isGeneratorObject(value)#
Returns true
if the value is a generator object as returned from a
built-in generator function.
Note that this only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.
function* foo() {}
const generator = foo();
util.types.isGeneratorObject(generator); // Returns true
util.types.isInt8Array(value)#
Returns true
if the value is a built-in Int8Array
instance.
util.types.isInt8Array(new ArrayBuffer()); // Returns false
util.types.isInt8Array(new Int8Array()); // Returns true
util.types.isInt8Array(new Float64Array()); // Returns false
util.types.isInt16Array(value)#
Returns true
if the value is a built-in Int16Array
instance.
util.types.isInt16Array(new ArrayBuffer()); // Returns false
util.types.isInt16Array(new Int16Array()); // Returns true
util.types.isInt16Array(new Float64Array()); // Returns false
util.types.isInt32Array(value)#
Returns true
if the value is a built-in Int32Array
instance.
util.types.isInt32Array(new ArrayBuffer()); // Returns false
util.types.isInt32Array(new Int32Array()); // Returns true
util.types.isInt32Array(new Float64Array()); // Returns false
util.types.isMap(value)#
Returns true
if the value is a built-in Map
instance.
util.types.isMap(new Map()); // Returns true
util.types.isMapIterator(value)#
Returns true
if the value is an iterator returned for a built-in
Map
instance.
const map = new Map();
util.types.isMapIterator(map.keys()); // Returns true
util.types.isMapIterator(map.values()); // Returns true
util.types.isMapIterator(map.entries()); // Returns true
util.types.isMapIterator(map[Symbol.iterator]()); // Returns true
util.types.isModuleNamespaceObject(value)#
Returns true
if the value is an instance of a Module Namespace Object.
import * as ns from './a.js';
util.types.isModuleNamespaceObject(ns); // Returns true
util.types.isNativeError(value)#
Returns true
if the value is an instance of a built-in Error
type.
util.types.isNativeError(new Error()); // Returns true
util.types.isNativeError(new TypeError()); // Returns true
util.types.isNativeError(new RangeError()); // Returns true
util.types.isNumberObject(value)#
Returns true
if the value is a number object, e.g. created
by new Number()
.
util.types.isNumberObject(0); // Returns false
util.types.isNumberObject(new Number(0)); // Returns true
util.types.isPromise(value)#
Returns true
if the value is a built-in Promise
.
util.types.isPromise(Promise.resolve(42)); // Returns true
util.types.isProxy(value)#
Returns true
if the value is a Proxy
instance.
const target = {};
const proxy = new Proxy(target, {});
util.types.isProxy(target); // Returns false
util.types.isProxy(proxy); // Returns true
util.types.isRegExp(value)#
Returns true
if the value is a regular expression object.
util.types.isRegExp(/abc/); // Returns true
util.types.isRegExp(new RegExp('abc')); // Returns true
util.types.isSet(value)#
Returns true
if the value is a built-in Set
instance.
util.types.isSet(new Set()); // Returns true
util.types.isSetIterator(value)#
Returns true
if the value is an iterator returned for a built-in
Set
instance.
const set = new Set();
util.types.isSetIterator(set.keys()); // Returns true
util.types.isSetIterator(set.values()); // Returns true
util.types.isSetIterator(set.entries()); // Returns true
util.types.isSetIterator(set[Symbol.iterator]()); // Returns true
util.types.isSharedArrayBuffer(value)#
Returns true
if the value is a built-in SharedArrayBuffer
instance.
This does not include ArrayBuffer
instances. Usually, it is
desirable to test for both; See util.types.isAnyArrayBuffer()
for that.
util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false
util.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true
util.types.isStringObject(value)#
Returns true
if the value is a string object, e.g. created
by new String()
.
util.types.isStringObject('foo'); // Returns false
util.types.isStringObject(new String('foo')); // Returns true
util.types.isSymbolObject(value)#
Returns true
if the value is a symbol object, created
by calling Object()
on a Symbol
primitive.
const symbol = Symbol('foo');
util.types.isSymbolObject(symbol); // Returns false
util.types.isSymbolObject(Object(symbol)); // Returns true
util.types.isTypedArray(value)#
Returns true
if the value is a built-in TypedArray
instance.
util.types.isTypedArray(new ArrayBuffer()); // Returns false
util.types.isTypedArray(new Uint8Array()); // Returns true
util.types.isTypedArray(new Float64Array()); // Returns true
See also ArrayBuffer.isView()
.
util.types.isUint8Array(value)#
Returns true
if the value is a built-in Uint8Array
instance.
util.types.isUint8Array(new ArrayBuffer()); // Returns false
util.types.isUint8Array(new Uint8Array()); // Returns true
util.types.isUint8Array(new Float64Array()); // Returns false
util.types.isUint8ClampedArray(value)#
Returns true
if the value is a built-in Uint8ClampedArray
instance.
util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false
util.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true
util.types.isUint8ClampedArray(new Float64Array()); // Returns false
util.types.isUint16Array(value)#
Returns true
if the value is a built-in Uint16Array
instance.
util.types.isUint16Array(new ArrayBuffer()); // Returns false
util.types.isUint16Array(new Uint16Array()); // Returns true
util.types.isUint16Array(new Float64Array()); // Returns false
util.types.isUint32Array(value)#
Returns true
if the value is a built-in Uint32Array
instance.
util.types.isUint32Array(new ArrayBuffer()); // Returns false
util.types.isUint32Array(new Uint32Array()); // Returns true
util.types.isUint32Array(new Float64Array()); // Returns false
util.types.isWeakMap(value)#
Returns true
if the value is a built-in WeakMap
instance.
util.types.isWeakMap(new WeakMap()); // Returns true
util.types.isWeakSet(value)#
Returns true
if the value is a built-in WeakSet
instance.
util.types.isWeakSet(new WeakSet()); // Returns true
util.types.isWebAssemblyCompiledModule(value)#
Returns true
if the value is a built-in WebAssembly.Module
instance.
const module = new WebAssembly.Module(wasmBuffer);
util.types.isWebAssemblyCompiledModule(module); // Returns true
Deprecated APIs#
The following APIs are deprecated and should no longer be used. Existing applications and modules should be updated to find alternative approaches.
util._extend(target, source)#
Object.assign()
instead.The util._extend()
method was never intended to be used outside of internal
Node.js modules. The community found and used it anyway.
It is deprecated and should not be used in new code. JavaScript comes with very
similar built-in functionality through Object.assign()
.
util.debug(string)#
console.error()
instead.string
<string> The message to print tostderr
Deprecated predecessor of console.error
.
util.error([...strings])#
console.error()
instead....strings
<string> The message to print tostderr
Deprecated predecessor of console.error
.
util.isArray(object)#
Array.isArray()
instead.Alias for Array.isArray()
.
Returns true
if the given object
is an Array
. Otherwise, returns false
.
const util = require('util');
util.isArray([]);
// Returns: true
util.isArray(new Array());
// Returns: true
util.isArray({});
// Returns: false
util.isBoolean(object)[src]#
typeof value === 'boolean'
instead.Returns true
if the given object
is a Boolean
. Otherwise, returns false
.
const util = require('util');
util.isBoolean(1);
// Returns: false
util.isBoolean(0);
// Returns: false
util.isBoolean(false);
// Returns: true
util.isBuffer(object)#
Buffer.isBuffer()
instead.Returns true
if the given object
is a Buffer
. Otherwise, returns false
.
const util = require('util');
util.isBuffer({ length: 0 });
// Returns: false
util.isBuffer([]);
// Returns: false
util.isBuffer(Buffer.from('hello world'));
// Returns: true
util.isDate(object)#
util.types.isDate()
instead.Returns true
if the given object
is a Date
. Otherwise, returns false
.
const util = require('util');
util.isDate(new Date());
// Returns: true
util.isDate(Date());
// false (without 'new' returns a String)
util.isDate({});
// Returns: false
util.isError(object)#
util.types.isNativeError()
instead.Returns true
if the given object
is an Error
. Otherwise, returns
false
.
const util = require('util');
util.isError(new Error());
// Returns: true
util.isError(new TypeError());
// Returns: true
util.isError({ name: 'Error', message: 'an error occurred' });
// Returns: false
Note that this method relies on Object.prototype.toString()
behavior. It is
possible to obtain an incorrect result when the object
argument manipulates
@@toStringTag
.
const util = require('util');
const obj = { name: 'Error', message: 'an error occurred' };
util.isError(obj);
// Returns: false
obj[Symbol.toStringTag] = 'Error';
util.isError(obj);
// Returns: true
util.isFunction(object)[src]#
typeof value === 'function'
instead.Returns true
if the given object
is a Function
. Otherwise, returns
false
.
const util = require('util');
function Foo() {}
const Bar = () => {};
util.isFunction({});
// Returns: false
util.isFunction(Foo);
// Returns: true
util.isFunction(Bar);
// Returns: true
util.isNull(object)[src]#
value === null
instead.Returns true
if the given object
is strictly null
. Otherwise, returns
false
.
const util = require('util');
util.isNull(0);
// Returns: false
util.isNull(undefined);
// Returns: false
util.isNull(null);
// Returns: true
util.isNullOrUndefined(object)[src]#
value === undefined || value === null
instead.Returns true
if the given object
is null
or undefined
. Otherwise,
returns false
.
const util = require('util');
util.isNullOrUndefined(0);
// Returns: false
util.isNullOrUndefined(undefined);
// Returns: true
util.isNullOrUndefined(null);
// Returns: true
util.isNumber(object)[src]#
typeof value === 'number'
instead.Returns true
if the given object
is a Number
. Otherwise, returns false
.
const util = require('util');
util.isNumber(false);
// Returns: false
util.isNumber(Infinity);
// Returns: true
util.isNumber(0);
// Returns: true
util.isNumber(NaN);
// Returns: true
util.isObject(object)[src]#
value !== null && typeof value === 'object'
instead.Returns true
if the given object
is strictly an Object
and not a
Function
(even though functions are objects in JavaScript).
Otherwise, returns false
.
const util = require('util');
util.isObject(5);
// Returns: false
util.isObject(null);
// Returns: false
util.isObject({});
// Returns: true
util.isObject(() => {});
// Returns: false
util.isPrimitive(object)[src]#
(typeof value !== 'object' && typeof value !== 'function') || value === null
instead.Returns true
if the given object
is a primitive type. Otherwise, returns
false
.
const util = require('util');
util.isPrimitive(5);
// Returns: true
util.isPrimitive('foo');
// Returns: true
util.isPrimitive(false);
// Returns: true
util.isPrimitive(null);
// Returns: true
util.isPrimitive(undefined);
// Returns: true
util.isPrimitive({});
// Returns: false
util.isPrimitive(() => {});
// Returns: false
util.isPrimitive(/^$/);
// Returns: false
util.isPrimitive(new Date());
// Returns: false
util.isRegExp(object)#
Returns true
if the given object
is a RegExp
. Otherwise, returns false
.
const util = require('util');
util.isRegExp(/some regexp/);
// Returns: true
util.isRegExp(new RegExp('another regexp'));
// Returns: true
util.isRegExp({});
// Returns: false
util.isString(object)[src]#
typeof value === 'string'
instead.Returns true
if the given object
is a string
. Otherwise, returns false
.
const util = require('util');
util.isString('');
// Returns: true
util.isString('foo');
// Returns: true
util.isString(String('foo'));
// Returns: true
util.isString(5);
// Returns: false
util.isSymbol(object)[src]#
typeof value === 'symbol'
instead.Returns true
if the given object
is a Symbol
. Otherwise, returns false
.
const util = require('util');
util.isSymbol(5);
// Returns: false
util.isSymbol('foo');
// Returns: false
util.isSymbol(Symbol('foo'));
// Returns: true
util.isUndefined(object)[src]#
value === undefined
instead.Returns true
if the given object
is undefined
. Otherwise, returns false
.
const util = require('util');
const foo = undefined;
util.isUndefined(5);
// Returns: false
util.isUndefined(foo);
// Returns: true
util.isUndefined(null);
// Returns: false
util.log(string)[src]#
string
<string>
The util.log()
method prints the given string
to stdout
with an included
timestamp.
const util = require('util');
util.log('Timestamped message.');
util.print([...strings])#
console.log()
instead.Deprecated predecessor of console.log
.
util.puts([...strings])#
console.log()
instead.Deprecated predecessor of console.log
.