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Code Editor : util.md

# Util

> Stability: 2 - Stable

The `node:util` module supports the needs of Node.js internal APIs. Many of the
utilities are useful for application and module developers as well. To access
it:

```js
const util = require('node:util');
```

## `util.callbackify(original)`

* `original` {Function} An `async` 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.

```js
const util = require('node:util');

async function fn() {
  return 'hello world';
}
const callbackFunction = util.callbackify(fn);

callbackFunction((err, ret) => {
  if (err) throw err;
  console.log(ret);
});
```

Will print:

```text
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`.

```js
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 && Object.hasOwn(err, 'reason') && err.reason === null;  // true
});
```

## `util.debuglog(section[, callback])`

* `section` {string} A string identifying the portion of the application for
  which the `debuglog` function is being created.
* `callback` {Function} A callback invoked the first time the logging function
  is called with a function argument that is a more optimized logging function.
* 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.

```js
const util = require('node: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:

```console
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:

```js
const util = require('node: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:

```console
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`.

The optional `callback` argument can be used to replace the logging function
with a different function that doesn't have any initialization or
unnecessary wrapping.

```js
const util = require('node:util');
let debuglog = util.debuglog('internals', (debug) => {
  // Replace with a logging function that optimizes out
  // testing if the section is enabled
  debuglog = debug;
});
```

### `debuglog().enabled`

* {boolean}

The `util.debuglog().enabled` getter is used to create a test that can be used
in conditionals 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 value will be `true`. If not, then the returned value will be
`false`.

```js
const util = require('node:util');
const enabled = util.debuglog('foo').enabled;
if (enabled) {
  console.log('hello from foo [%d]', 123);
}
```

If this program is run with `NODE_DEBUG=foo` in the environment, then it will
output something like:

```console
hello from foo [123]
```

## `util.debug(section)`

Alias for `util.debuglog`. Usage allows for readability of that doesn't imply
logging when only using `util.debuglog().enabled`.

## `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.

```js
const util = require('node: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`.

```js
const util = require('node: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])`

* `format` {string} A `printf`-like format string.

The `util.format()` method returns a formatted string using the first argument
as a `printf`-like format string which can contain zero or more format
specifiers. Each specifier is replaced with the converted value from the
corresponding argument. Supported specifiers are:

* `%s`: `String` will be used to convert all values except `BigInt`, `Object`
  and `-0`. `BigInt` values will be represented with an `n` and Objects that
  have no user defined `toString` function are inspected using `util.inspect()`
  with options `{ depth: 0, colors: false, compact: 3 }`.
* `%d`: `Number` will be used to convert all values except `BigInt` and
  `Symbol`.
* `%i`: `parseInt(value, 10)` is used for all values except `BigInt` and
  `Symbol`.
* `%f`: `parseFloat(value)` is used for all values expect `Symbol`.
* `%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 to `util.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 to `util.inspect()` without options. This will show
  the full object not including non-enumerable properties and proxies.
* `%c`: `CSS`. This specifier is ignored and will skip any CSS passed in.
* `%%`: single percent sign (`'%'`). This does not consume an argument.
* Returns: {string} The formatted string

If a specifier does not have a corresponding argument, it is not replaced:

```js
util.format('%s:%s', 'foo');
// Returns: 'foo:%s'
```

Values that are not part of the format string are formatted using
`util.inspect()` if their type is not `string`.

If there are more arguments passed to the `util.format()` method than the
number of specifiers, the extra arguments are concatenated to the returned
string, separated by spaces:

```js
util.format('%s:%s', 'foo', 'bar', 'baz');
// Returns: 'foo:bar baz'
```

If the first argument does not contain a valid format specifier, `util.format()`
returns a string that is the concatenation of all arguments separated by spaces:

```js
util.format(1, 2, 3);
// Returns: '1 2 3'
```

If only one argument is passed to `util.format()`, it is returned as it is
without any formatting:

```js
util.format('%% %s');
// Returns: '%% %s'
```

`util.format()` is a synchronous method that is 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])`

* `inspectOptions` {Object}
* `format` {string}

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()`][].

```js
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)`

* `err` {number}
* Returns: {string}

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.

```js
fs.access('file/that/does/not/exist', (err) => {
  const name = util.getSystemErrorName(err.errno);
  console.error(name);  // ENOENT
});
```

## `util.getSystemErrorMap()`

* Returns: {Map}

Returns a Map of all system error codes available from the Node.js API.
The mapping between error codes and error names is platform-dependent.
See [Common System Errors][] for the names of common errors.

```js
fs.access('file/that/does/not/exist', (err) => {
  const errorMap = util.getSystemErrorMap();
  const name = errorMap.get(err.errno);
  console.error(name);  // ENOENT
});
```

## `util.inherits(constructor, superConstructor)`

> Stability: 3 - Legacy: Use ES2015 class syntax and `extends` keyword instead.

* `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`.

This mainly adds some input validation on top of
`Object.setPrototypeOf(constructor.prototype, superConstructor.prototype)`.
As an additional convenience, `superConstructor` will be accessible
through the `constructor.super_` property.

```js
const util = require('node:util');
const EventEmitter = require('node: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`:

```js
const EventEmitter = require('node: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 or `Object`.
* `options` {Object}
  * `showHidden` {boolean} If `true`, `object`'s non-enumerable symbols and
    properties are included in the formatted result. [`WeakMap`][] and
    [`WeakSet`][] entries are also included as well as user defined prototype
    properties (excluding method properties). **Default:** `false`.
  * `depth` {number} Specifies the number of times to recurse while formatting
    `object`. This is useful for inspecting large objects. To recurse up to
    the maximum call stack size pass `Infinity` or `null`.
    **Default:** `2`.
  * `colors` {boolean} If `true`, the output is styled with ANSI color
    codes. Colors are customizable. See [Customizing `util.inspect` colors][].
    **Default:** `false`.
  * `customInspect` {boolean} If `false`,
    `[util.inspect.custom](depth, opts, inspect)` functions are not invoked.
    **Default:** `true`.
  * `showProxy` {boolean} If `true`, `Proxy` inspection includes
    the [`target` and `handler`][] objects. **Default:** `false`.
  * `maxArrayLength` {integer} Specifies the maximum number of `Array`,
    [`TypedArray`][], [`WeakMap`][], and [`WeakSet`][] elements to include when
    formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or
    negative to show no elements. **Default:** `100`.
  * `maxStringLength` {integer} Specifies the maximum number of characters to
    include when formatting. Set to `null` or `Infinity` to show all elements.
    Set to `0` or negative to show no characters. **Default:** `10000`.
  * `breakLength` {integer} The length at which input values are split across
    multiple lines. Set to `Infinity` to format the input as a single line
    (in combination with `compact` set to `true` or any number >= `1`).
    **Default:** `80`.
  * `compact` {boolean|integer} Setting this to `false` causes each object key
    to be displayed on a new line. It will break on new lines in text that is
    longer than `breakLength`. If set to a number, the most `n` inner elements
    are united on a single line as long as all properties fit into
    `breakLength`. Short array elements are also grouped together. For more
    information, see the example below. **Default:** `3`.
  * `sorted` {boolean|Function} If set to `true` or a function, all properties
    of an object, and `Set` and `Map` entries are sorted in the resulting
    string. If set to `true` the [default sort][] is used. If set to a function,
    it is used as a [compare function][].
  * `getters` {boolean|string} If set to `true`, getters are inspected. If set
    to `'get'`, only getters without a corresponding setter are inspected. If
    set to `'set'`, only getters with a corresponding setter are inspected.
    This might cause side effects depending on the getter function.
    **Default:** `false`.
  * `numericSeparator` {boolean} If set to `true`, an underscore is used to
    separate every three digits in all bigints and numbers.
    **Default:** `false`.
* Returns: {string} The representation of `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 the result.
`util.inspect()` will use the constructor's name and/or `@@toStringTag` to make
an identifiable tag for an inspected value.

```js
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] {}'
```

Circular references point to their anchor by using a reference index:

```js
const { inspect } = require('node:util');

const obj = {};
obj.a = [obj];
obj.b = {};
obj.b.inner = obj.b;
obj.b.obj = obj;

console.log(inspect(obj));
// <ref *1> {
// a: [ [Circular *1] ],
// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }
// }
```

The following example inspects all properties of the `util` object:

```js
const util = require('node:util');

console.log(util.inspect(util, { showHidden: true, depth: null }));
```

The following example highlights the effect of the `compact` option:

```js
const util = require('node:util');

const o = {
  a: [1, 2, [[
    'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do ' +
      'eiusmod \ntempor 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 }));

// { a:
//   [ 1,
//     2,
//     [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line
//           'test',
//           'foo' ] ],
//     4 ],
//   b: Map(2) { 'za' => 1, 'zb' => 'test' } }

// Setting `compact` to false or an integer creates more reader friendly output.
console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 }));

// {
//   a: [
//     1,
//     2,
//     [
//       [
//         'Lorem ipsum dolor sit amet,\n' +
//           'consectetur adipiscing elit, sed do eiusmod \n' +
//           'tempor incididunt ut labore et dolore magna aliqua.',
//         'test',
//         'foo'
//       ]
//     ],
//     4
//   ],
//   b: Map(2) {
//     'za' => 1,
//     'zb' => 'test'
//   }
// }

// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a
// single line.
```

The `showHidden` option allows [`WeakMap`][] and [`WeakSet`][] entries to be
inspected. If there are more entries than `maxArrayLength`, there is no
guarantee which entries are displayed. That means retrieving the same
[`WeakSet`][] entries twice may result in different output. Furthermore, entries
with no remaining strong references may be garbage collected at any time.

```js
const { inspect } = require('node: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 ensures that an object's property insertion order does not
impact the result of `util.inspect()`.

```js
const { inspect } = require('node:util');
const assert = require('node:assert');

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 }),
);
```

The `numericSeparator` option adds an underscore every three digits to all
numbers.

```js
const { inspect } = require('node:util');

const thousand = 1_000;
const million = 1_000_000;
const bigNumber = 123_456_789n;
const bigDecimal = 1_234.123_45;

console.log(thousand, million, bigNumber, bigDecimal);
// 1_000 1_000_000 123_456_789n 1_234.123_45
```

`util.inspect()` is a synchronous method intended for debugging. Its maximum
output length is approximately 128 MiB. Inputs that result in longer output will
be truncated.

### 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:

* `bigint`: `yellow`
* `boolean`: `yellow`
* `date`: `magenta`
* `module`: `underline`
* `name`: (no styling)
* `null`: `bold`
* `number`: `yellow`
* `regexp`: `red`
* `special`: `cyan` (e.g., `Proxies`)
* `string`: `green`
* `symbol`: `green`
* `undefined`: `grey`

Color styling uses ANSI control codes that may not be supported on all
terminals. To verify color support use [`tty.hasColors()`][].

Predefined control codes are listed below (grouped as "Modifiers", "Foreground
colors", and "Background colors").

#### Modifiers

Modifier support varies throughout different terminals. They will mostly be
ignored, if not supported.

* `reset` - Resets all (color) modifiers to their defaults
* **bold** - Make text bold
* _italic_ - Make text italic
* underline - Make text underlined
* ~~strikethrough~~ - Puts a horizontal line through the center of the text
 (Alias: `strikeThrough`, `crossedout`, `crossedOut`)
* `hidden` - Prints the text, but makes it invisible (Alias: conceal)
* dim - Decreased color intensity (Alias:
 `faint`)
* overlined - Make text overlined
* blink - Hides and shows the text in an interval
* inverse - Swap foreground and
 background colors (Alias: `swapcolors`, `swapColors`)
* doubleunderline - Make text
 double underlined (Alias: `doubleUnderline`)
* framed - Draw a frame around the text

#### Foreground colors

* `black`
* `red`
* `green`
* `yellow`
* `blue`
* `magenta`
* `cyan`
* `white`
* `gray` (alias: `grey`, `blackBright`)
* `redBright`
* `greenBright`
* `yellowBright`
* `blueBright`
* `magentaBright`
* `cyanBright`
* `whiteBright`

#### Background colors

* `bgBlack`
* `bgRed`
* `bgGreen`
* `bgYellow`
* `bgBlue`
* `bgMagenta`
* `bgCyan`
* `bgWhite`
* `bgGray` (alias: `bgGrey`, `bgBlackBright`)
* `bgRedBright`
* `bgGreenBright`
* `bgYellowBright`
* `bgBlueBright`
* `bgMagentaBright`
* `bgCyanBright`
* `bgWhiteBright`

### Custom inspection functions on objects

Objects may also define their own
[`[util.inspect.custom](depth, opts, inspect)`][util.inspect.custom] function,
which `util.inspect()` will invoke and use the result of when inspecting
the object.

```js
const util = require('node:util');

class Box {
  constructor(value) {
    this.value = value;
  }

[util.inspect.custom](depth, options, inspect) {
 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 = 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, inspect)` functions typically return
a string but may return a value of any type that will be formatted accordingly
by `util.inspect()`.

```js
const util = require('node: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][global symbol registry] and can be
accessed in any environment as `Symbol.for('nodejs.util.inspect.custom')`.

Using this allows code to be written in a portable fashion, so that the custom
inspect function is used in an Node.js environment and ignored in the browser.
The `util.inspect()` function itself is passed as third argument to the custom
inspect function to allow further portability.

```js
const customInspectSymbol = Symbol.for('nodejs.util.inspect.custom');

class Password {
  constructor(value) {
    this.value = value;
  }

toString() {
    return 'xxxxxxxx';
  }

[customInspectSymbol](depth, inspectOptions, 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.

```js
const util = require('node: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)`

* `val1` {any}
* `val2` {any}
* Returns: {boolean}

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.

## Class: `util.MIMEType`

> Stability: 1 - Experimental

An implementation of [the MIMEType class](https://bmeck.github.io/node-proposal-mime-api/).

In accordance with browser conventions, all properties of `MIMEType` objects
are implemented as getters and setters on the class prototype, rather than as
data properties on the object itself.

A MIME string is a structured string containing multiple meaningful
components. When parsed, a `MIMEType` object is returned containing
properties for each of these components.

### Constructor: `new MIMEType(input)`

* `input` {string} The input MIME to parse

Creates a new `MIMEType` object by parsing the `input`.

```mjs
import { MIMEType } from 'node:util';

const myMIME = new MIMEType('text/plain');
```

```cjs
const { MIMEType } = require('node:util');

const myMIME = new MIMEType('text/plain');
```

A `TypeError` will be thrown if the `input` is not a valid MIME. Note
that an effort will be made to coerce the given values into strings. For
instance:

```mjs
import { MIMEType } from 'node:util';
const myMIME = new MIMEType({ toString: () => 'text/plain' });
console.log(String(myMIME));
// Prints: text/plain
```

```cjs
const { MIMEType } = require('node:util');
const myMIME = new MIMEType({ toString: () => 'text/plain' });
console.log(String(myMIME));
// Prints: text/plain
```

#### `mime.type`

* {string}

Gets and sets the type portion of the MIME.

```mjs
import { MIMEType } from 'node:util';

const myMIME = new MIMEType('text/javascript');
console.log(myMIME.type);
// Prints: text
myMIME.type = 'application';
console.log(myMIME.type);
// Prints: application
console.log(String(myMIME));
// Prints: application/javascript
```

```cjs
const { MIMEType } = require('node:util');

#### `mime.subtype`

* {string}

Gets and sets the subtype portion of the MIME.

```mjs
import { MIMEType } from 'node:util';

const myMIME = new MIMEType('text/ecmascript');
console.log(myMIME.subtype);
// Prints: ecmascript
myMIME.subtype = 'javascript';
console.log(myMIME.subtype);
// Prints: javascript
console.log(String(myMIME));
// Prints: text/javascript
```

```cjs
const { MIMEType } = require('node:util');

#### `mime.essence`

* {string}

Gets the essence of the MIME. This property is read only.
Use `mime.type` or `mime.subtype` to alter the MIME.

```mjs
import { MIMEType } from 'node:util';

const myMIME = new MIMEType('text/javascript;key=value');
console.log(myMIME.essence);
// Prints: text/javascript
myMIME.type = 'application';
console.log(myMIME.essence);
// Prints: application/javascript
console.log(String(myMIME));
// Prints: application/javascript;key=value
```

```cjs
const { MIMEType } = require('node:util');

#### `mime.params`

* {MIMEParams}

Gets the [`MIMEParams`][] object representing the
parameters of the MIME. This property is read-only. See
[`MIMEParams`][] documentation for details.

#### `mime.toString()`

* Returns: {string}

The `toString()` method on the `MIMEType` object returns the serialized MIME.

Because of the need for standard compliance, this method does not allow users
to customize the serialization process of the MIME.

#### `mime.toJSON()`

* Returns: {string}

Alias for [`mime.toString()`][].

This method is automatically called when an `MIMEType` object is serialized
with [`JSON.stringify()`][].

```mjs
import { MIMEType } from 'node:util';

const myMIMES = [
  new MIMEType('image/png'),
  new MIMEType('image/gif'),
];
console.log(JSON.stringify(myMIMES));
// Prints: ["image/png", "image/gif"]
```

```cjs
const { MIMEType } = require('node:util');

const myMIMES = [
  new MIMEType('image/png'),
  new MIMEType('image/gif'),
];
console.log(JSON.stringify(myMIMES));
// Prints: ["image/png", "image/gif"]
```

### Class: `util.MIMEParams`

The `MIMEParams` API provides read and write access to the parameters of a
`MIMEType`.

#### Constructor: `new MIMEParams()`

Creates a new `MIMEParams` object by with empty parameters

```mjs
import { MIMEParams } from 'node:util';

const myParams = new MIMEParams();
```

```cjs
const { MIMEParams } = require('node:util');

const myParams = new MIMEParams();
```

#### `mimeParams.delete(name)`

* `name` {string}

Remove all name-value pairs whose name is `name`.

#### `mimeParams.entries()`

* Returns: {Iterator}

Returns an iterator over each of the name-value pairs in the parameters.
Each item of the iterator is a JavaScript `Array`. The first item of the array
is the `name`, the second item of the array is the `value`.

#### `mimeParams.get(name)`

* `name` {string}
* Returns: {string} or `null` if there is no name-value pair with the given
  `name`.

Returns the value of the first name-value pair whose name is `name`. If there
are no such pairs, `null` is returned.

#### `mimeParams.has(name)`

* `name` {string}
* Returns: {boolean}

Returns `true` if there is at least one name-value pair whose name is `name`.

#### `mimeParams.keys()`

* Returns: {Iterator}

Returns an iterator over the names of each name-value pair.

```mjs
import { MIMEType } from 'node:util';

const { params } = new MIMEType('text/plain;foo=0;bar=1');
for (const name of params.keys()) {
  console.log(name);
}
// Prints:
//   foo
//   bar
```

```cjs
const { MIMEType } = require('node:util');

const { params } = new MIMEType('text/plain;foo=0;bar=1');
for (const name of params.keys()) {
  console.log(name);
}
// Prints:
//   foo
//   bar
```

#### `mimeParams.set(name, value)`

* `name` {string}
* `value` {string}

Sets the value in the `MIMEParams` object associated with `name` to
`value`. If there are any pre-existing name-value pairs whose names are `name`,
set the first such pair's value to `value`.

```mjs
import { MIMEType } from 'node:util';

const { params } = new MIMEType('text/plain;foo=0;bar=1');
params.set('foo', 'def');
params.set('baz', 'xyz');
console.log(params.toString());
// Prints: foo=def&bar=1&baz=xyz
```

```cjs
const { MIMEType } = require('node:util');

const { params } = new MIMEType('text/plain;foo=0;bar=1');
params.set('foo', 'def');
params.set('baz', 'xyz');
console.log(params.toString());
// Prints: foo=def&bar=1&baz=xyz
```

#### `mimeParams.values()`

* Returns: {Iterator}

Returns an iterator over the values of each name-value pair.

#### `mimeParams[@@iterator]()`

* Returns: {Iterator}

Alias for [`mimeParams.entries()`][].

```mjs
import { MIMEType } from 'node:util';

const { params } = new MIMEType('text/plain;foo=bar;xyz=baz');
for (const [name, value] of params) {
  console.log(name, value);
}
// Prints:
//   foo bar
//   xyz baz
```

```cjs
const { MIMEType } = require('node:util');

const { params } = new MIMEType('text/plain;foo=bar;xyz=baz');
for (const [name, value] of params) {
  console.log(name, value);
}
// Prints:
//   foo bar
//   xyz baz
```

## `util.parseArgs([config])`

> Stability: 1 - Experimental

* `config` {Object} Used to provide arguments for parsing and to configure
  the parser. `config` supports the following properties:
  * `args` {string\[]} array of argument strings. **Default:** `process.argv`
    with `execPath` and `filename` removed.
  * `options` {Object} Used to describe arguments known to the parser.
    Keys of `options` are the long names of options and values are an
    {Object} accepting the following properties:
    * `type` {string} Type of argument, which must be either `boolean` or `string`.
    * `multiple` {boolean} Whether this option can be provided multiple
      times. If `true`, all values will be collected in an array. If
      `false`, values for the option are last-wins. **Default:** `false`.
    * `short` {string} A single character alias for the option.
    * `default` {string | boolean | string\[] | boolean\[]} The default option
      value when it is not set by args. It must be of the same type as the
      `type` property. When `multiple` is `true`, it must be an array.
  * `strict` {boolean} Should an error be thrown when unknown arguments
    are encountered, or when arguments are passed that do not match the
    `type` configured in `options`.
    **Default:** `true`.
  * `allowPositionals` {boolean} Whether this command accepts positional
    arguments.
    **Default:** `false` if `strict` is `true`, otherwise `true`.
  * `tokens` {boolean} Return the parsed tokens. This is useful for extending
    the built-in behavior, from adding additional checks through to reprocessing
    the tokens in different ways.
    **Default:** `false`.

* Returns: {Object} The parsed command line arguments:
  * `values` {Object} A mapping of parsed option names with their {string}
    or {boolean} values.
  * `positionals` {string\[]} Positional arguments.
  * `tokens` {Object\[] | undefined} See [parseArgs tokens](#parseargs-tokens)
    section. Only returned if `config` includes `tokens: true`.

Provides a higher level API for command-line argument parsing than interacting
with `process.argv` directly. Takes a specification for the expected arguments
and returns a structured object with the parsed options and positionals.

```mjs
import { parseArgs } from 'node:util';
const args = ['-f', '--bar', 'b'];
const options = {
  foo: {
    type: 'boolean',
    short: 'f',
  },
  bar: {
    type: 'string',
  },
};
const {
  values,
  positionals,
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```

```cjs
const { parseArgs } = require('node:util');
const args = ['-f', '--bar', 'b'];
const options = {
  foo: {
    type: 'boolean',
    short: 'f',
  },
  bar: {
    type: 'string',
  },
};
const {
  values,
  positionals,
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```

`util.parseArgs` is experimental and behavior may change. Join the
conversation in [pkgjs/parseargs][] to contribute to the design.

### `parseArgs` `tokens`

Detailed parse information is available for adding custom behaviors by
specifying `tokens: true` in the configuration.
The returned tokens have properties describing:

* all tokens
  * `kind` {string} One of 'option', 'positional', or 'option-terminator'.
  * `index` {number} Index of element in `args` containing token. So the
    source argument for a token is `args[token.index]`.
* option tokens
  * `name` {string} Long name of option.
  * `rawName` {string} How option used in args, like `-f` of `--foo`.
  * `value` {string | undefined} Option value specified in args.
    Undefined for boolean options.
  * `inlineValue` {boolean | undefined} Whether option value specified inline,
    like `--foo=bar`.
* positional tokens
  * `value` {string} The value of the positional argument in args (i.e. `args[index]`).
* option-terminator token

The returned tokens are in the order encountered in the input args. Options
that appear more than once in args produce a token for each use. Short option
groups like `-xy` expand to a token for each option. So `-xxx` produces
three tokens.

For example to use the returned tokens to add support for a negated option
like `--no-color`, the tokens can be reprocessed to change the value stored
for the negated option.

```mjs
import { parseArgs } from 'node:util';

const options = {
  'color': { type: 'boolean' },
  'no-color': { type: 'boolean' },
  'logfile': { type: 'string' },
  'no-logfile': { type: 'boolean' },
};
const { values, tokens } = parseArgs({ options, tokens: true });

// Reprocess the option tokens and overwrite the returned values.
tokens
  .filter((token) => token.kind === 'option')
  .forEach((token) => {
    if (token.name.startsWith('no-')) {
      // Store foo:false for --no-foo
      const positiveName = token.name.slice(3);
      values[positiveName] = false;
      delete values[token.name];
    } else {
      // Resave value so last one wins if both --foo and --no-foo.
      values[token.name] = token.value ?? true;
    }
  });

const color = values.color;
const logfile = values.logfile ?? 'default.log';

console.log({ logfile, color });
```

```cjs
const { parseArgs } = require('node:util');

const color = values.color;
const logfile = values.logfile ?? 'default.log';

console.log({ logfile, color });
```

Example usage showing negated options, and when an option is used
multiple ways then last one wins.

```console
$ node negate.js
{ logfile: 'default.log', color: undefined }
$ node negate.js --no-logfile --no-color
{ logfile: false, color: false }
$ node negate.js --logfile=test.log --color
{ logfile: 'test.log', color: true }
$ node negate.js --no-logfile --logfile=test.log --color --no-color
{ logfile: 'test.log', color: false }
```

## `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.

```js
const util = require('node:util');
const fs = require('node: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:

```js
const util = require('node:util');
const fs = require('node: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.

Using `promisify()` on class methods or other methods that use `this` may not
work as expected unless handled specially:

```js
const util = require('node:util');

class Foo {
  constructor() {
    this.a = 42;
  }

bar(callback) {
    callback(null, this.a);
  }
}

const foo = new Foo();

const naiveBar = util.promisify(foo.bar);
// TypeError: Cannot read property 'a' of undefined
// naiveBar().then(a => console.log(a));

naiveBar.call(foo).then((a) => console.log(a)); // '42'

const bindBar = naiveBar.bind(foo);
bindBar().then((a) => console.log(a)); // '42'
```

### Custom promisified functions

Using the `util.promisify.custom` symbol one can override the return value of
[`util.promisify()`][]:

```js
const util = require('node: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)`:

```js
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`

* {symbol} that can be used to declare custom promisified variants of functions,
  see [Custom promisified functions][].

In addition to being accessible through `util.promisify.custom`, this
symbol is [registered globally][global symbol registry] and can be
accessed in any environment as `Symbol.for('nodejs.util.promisify.custom')`.

For example, with a function that takes in
`(foo, onSuccessCallback, onErrorCallback)`:

```js
const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom');

doSomething[kCustomPromisifiedSymbol] = (foo) => {
  return new Promise((resolve, reject) => {
    doSomething(foo, resolve, reject);
  });
};
```

## `util.stripVTControlCharacters(str)`

* `str` {string}
* Returns: {string}

Returns `str` with any ANSI escape codes removed.

```js
console.log(util.stripVTControlCharacters('\u001B[4mvalue\u001B[0m'));
// Prints "value"
```

## Class: `util.TextDecoder`

An implementation of the [WHATWG Encoding Standard][] `TextDecoder` API.

```js
const decoder = new TextDecoder();
const u8arr = new Uint8Array([72, 101, 108, 108, 111]);
console.log(decoder.decode(u8arr)); // Hello
```

### 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.
(see [Internationalization][])

#### Encodings supported by default (with 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'`                                                                                      |

#### Encodings supported when Node.js is built with the `small-icu` option

| Encoding     | Aliases                         |
| ------------ | ------------------------------- |
| `'utf-8'`    | `'unicode-1-1-utf-8'`, `'utf8'` |
| `'utf-16le'` | `'utf-16'`                      |
| `'utf-16be'` |                                 |

#### Encodings supported when ICU is disabled

| Encoding     | Aliases                         |
| ------------ | ------------------------------- |
| `'utf-8'`    | `'unicode-1-1-utf-8'`, `'utf8'` |
| `'utf-16le'` | `'utf-16'`                      |

The `'iso-8859-16'` encoding listed in the [WHATWG Encoding Standard][]
is not supported.

### `new TextDecoder([encoding[, options]])`

* `encoding` {string} Identifies the `encoding` that this `TextDecoder` instance
  supports. **Default:** `'utf-8'`.
* `options` {Object}
  * `fatal` {boolean} `true` if decoding failures are fatal.
    This option is not supported when ICU is disabled
    (see [Internationalization][]). **Default:** `false`.
  * `ignoreBOM` {boolean} When `true`, the `TextDecoder` will include the byte
    order mark in the decoded result. When `false`, the byte order mark will
    be removed from the output. This option is only used when `encoding` is
    `'utf-8'`, `'utf-16be'`, or `'utf-16le'`. **Default:** `false`.

Creates a new `TextDecoder` instance. The `encoding` may specify one of the
supported encodings or an alias.

The `TextDecoder` class is also available on the global object.

### `textDecoder.decode([input[, options]])`

* `input` {ArrayBuffer|DataView|TypedArray} An `ArrayBuffer`, `DataView`, or
  `TypedArray` 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`

* {string}

The encoding supported by the `TextDecoder` instance.

### `textDecoder.fatal`

* {boolean}

The value will be `true` if decoding errors result in a `TypeError` being
thrown.

### `textDecoder.ignoreBOM`

* {boolean}

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.

```js
const encoder = new TextEncoder();
const uint8array = encoder.encode('this is some data');
```

The `TextEncoder` class is also available on the global object.

### `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.encodeInto(src, dest)`

* `src` {string} The text to encode.
* `dest` {Uint8Array} The array to hold the encode result.
* Returns: {Object}
  * `read` {number} The read Unicode code units of src.
  * `written` {number} The written UTF-8 bytes of dest.

UTF-8 encodes the `src` string to the `dest` Uint8Array and returns an object
containing the read Unicode code units and written UTF-8 bytes.

```js
const encoder = new TextEncoder();
const src = 'this is some data';
const dest = new Uint8Array(10);
const { read, written } = encoder.encodeInto(src, dest);
```

### `textEncoder.encoding`

* {string}

The encoding supported by the `TextEncoder` instance. Always set to `'utf-8'`.

## `util.toUSVString(string)`

* `string` {string}

Returns the `string` after replacing any surrogate code points
(or equivalently, any unpaired surrogate code units) with the
Unicode "replacement character" U+FFFD.

## `util.transferableAbortController()`

> Stability: 1 - Experimental

Creates and returns an {AbortController} instance whose {AbortSignal} is marked
as transferable and can be used with `structuredClone()` or `postMessage()`.

## `util.transferableAbortSignal(signal)`

> Stability: 1 - Experimental

* `signal` {AbortSignal}
* Returns: {AbortSignal}

Marks the given {AbortSignal} as transferable so that it can be used with
`structuredClone()` and `postMessage()`.

```js
const signal = transferableAbortSignal(AbortSignal.timeout(100));
const channel = new MessageChannel();
channel.port2.postMessage(signal, [signal]);
```

## `util.aborted(signal, resource)`

> Stability: 1 - Experimental

* `signal` {AbortSignal}
* `resource` {Object} Any non-null entity, reference to which is held weakly.
* Returns: {Promise}

Listens to abort event on the provided `signal` and
returns a promise that is fulfilled when the `signal` is
aborted. If the passed `resource` is garbage collected before the `signal` is
aborted, the returned promise shall remain pending indefinitely.

```cjs
const { aborted } = require('node:util');

const dependent = obtainSomethingAbortable();

aborted(dependent.signal, dependent).then(() => {
  // Do something when dependent is aborted.
});

dependent.on('event', () => {
  dependent.abort();
});
```

```mjs
import { aborted } from 'node:util';

const dependent = obtainSomethingAbortable();

aborted(dependent.signal, dependent).then(() => {
  // Do something when dependent is aborted.
});

dependent.on('event', () => {
  dependent.abort();
});
```

## `util.types`

`util.types` provides 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.

The API is accessible via `require('node:util').types` or `require('node:util/types')`.

### `util.types.isAnyArrayBuffer(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is a built-in [`ArrayBuffer`][] or
[`SharedArrayBuffer`][] instance.

See also [`util.types.isArrayBuffer()`][] and
[`util.types.isSharedArrayBuffer()`][].

```js
util.types.isAnyArrayBuffer(new ArrayBuffer());  // Returns true
util.types.isAnyArrayBuffer(new SharedArrayBuffer());  // Returns true
```

### `util.types.isArrayBufferView(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is an instance of one of the [`ArrayBuffer`][]
views, such as typed array objects or [`DataView`][]. Equivalent to
[`ArrayBuffer.isView()`][].

```js
util.types.isArrayBufferView(new Int8Array());  // true
util.types.isArrayBufferView(Buffer.from('hello world')); // true
util.types.isArrayBufferView(new DataView(new ArrayBuffer(16)));  // true
util.types.isArrayBufferView(new ArrayBuffer());  // false
```

### `util.types.isArgumentsObject(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is an `arguments` object.

```js
function foo() {
  util.types.isArgumentsObject(arguments);  // Returns true
}
```

### `util.types.isArrayBuffer(value)`

* `value` {any}
* Returns: {boolean}

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.

```js
util.types.isArrayBuffer(new ArrayBuffer());  // Returns true
util.types.isArrayBuffer(new SharedArrayBuffer());  // Returns false
```

### `util.types.isAsyncFunction(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is an [async function][].
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.

```js
util.types.isAsyncFunction(function foo() {});  // Returns false
util.types.isAsyncFunction(async function foo() {});  // Returns true
```

### `util.types.isBigInt64Array(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is a `BigInt64Array` instance.

```js
util.types.isBigInt64Array(new BigInt64Array());   // Returns true
util.types.isBigInt64Array(new BigUint64Array());  // Returns false
```

### `util.types.isBigUint64Array(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is a `BigUint64Array` instance.

```js
util.types.isBigUint64Array(new BigInt64Array());   // Returns false
util.types.isBigUint64Array(new BigUint64Array());  // Returns true
```

### `util.types.isBooleanObject(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is a boolean object, e.g. created
by `new Boolean()`.

```js
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)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is any boxed primitive object, e.g. created
by `new Boolean()`, `new String()` or `Object(Symbol())`.

For example:

```js
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.isCryptoKey(value)`

* `value` {Object}
* Returns: {boolean}

Returns `true` if `value` is a {CryptoKey}, `false` otherwise.

### `util.types.isDataView(value)`

* `value` {any}
* Returns: {boolean}

Returns `true` if the value is a built-in [`DataView`][] instance.

```js
const ab = new ArrayBuffer(20);
util.types.isDataView(new DataView(ab));  // Returns true
util.types.isDataView(new Float64Array());  // Returns false
```

${this.title}

Code Editor : util.md