Promisify


Assembly	`Xantham.Fable.Node`


`Fn`
`Fn10`
`Fn2`
`Fn3`
`Fn4`
`Fn5`
`Fn6`
`Fn7`
`Fn8`
`Fn9`
`Result`
`Result2`
`Result3`
`Result4`
`Result5`
`Result6`
`Result7`
`Result8`

abstract member custom: Symbol

That can be used to declare custom promisified variants of functions.

abstract member Invoke (fn: Function) : 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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3, 'T4, 'T5> (fn: Fn10<'T1,'T2,'T3,'T4,'T5>) : Result8<'T1,'T2,'T3,'T4,'T5>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3, 'T4, 'T5, 'TResult> (fn: Fn9<'T1,'T2,'T3,'T4,'T5,'TResult>) : Result7<'T1,'T2,'T3,'T4,'T5,'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3, 'T4> (fn: Fn8<'T1,'T2,'T3,'T4>) : Result6<'T1,'T2,'T3,'T4>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3, 'T4, 'TResult> (fn: Fn7<'T1,'T2,'T3,'T4,'TResult>) : Result5<'T1,'T2,'T3,'T4,'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3> (fn: Fn6<'T1,'T2,'T3>) : Result4<'T1,'T2,'T3>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'T3, 'TResult> (fn: Fn5<'T1,'T2,'T3,'TResult>) : Result3<'T1,'T2,'T3,'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2> (fn: Fn4<'T1,'T2>) : Result2<'T1,'T2>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'T2, 'TResult> (fn: Fn3<'T1,'T2,'TResult>) : Result<'T1,'T2,'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1> (fn: Fn2<'T1>) : 'T1 -> Promise<unit>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'T1, 'TResult> (fn: Fn<'T1,'TResult>) : 'T1 -> Promise<'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke (fn: (obj option -> unit) -> unit) : unit -> Promise<unit>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'TResult> (fn: Callback<'TResult> -> unit) : unit -> Promise<'TResult>

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

abstract member Invoke<'TCustom> (fn: U2<CustomPromisifyLegacy<'TCustom>,CustomPromisifySymbol<'TCustom>>) : 'TCustom

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.

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);
promisifiedStat('.').then((stats) => {
// Do something with `stats`
}).catch((error) => {
// Handle the error.
});

Or, equivalently using async functions:

import { promisify } from 'node:util';
import { stat } from 'node:fs';

const promisifiedStat = promisify(stat);

async function callStat() {
const stats = await promisifiedStat('.');
console.log(`This directory is owned by ${stats.uid}`);
}

callStat();

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:

import { promisify } from 'node:util';

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

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

const foo = new Foo();

const naiveBar = promisify(foo.bar);
// TypeError: Cannot read properties of undefined (reading 'a')
// 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'

@since v8.0.0

Promisify

Declared inside

Properties

Methods