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Promisify a callback-style function


$ npm install pify


const fs = require('fs');
const pify = require('pify');

(async () => {
	// Promisify a single function.
	const data = await pify(fs.readFile)('package.json', 'utf8');
	//=> 'pify'

	// Promisify all methods in a module.
	const data2 = await pify(fs).readFile('package.json', 'utf8');
	//=> 'pify'


pify(input, options?)

Returns a Promise wrapped version of the supplied function or module.


Type: Function | object

Callback-style function or module whose methods you want to promisify.


Type: object


Type: boolean
Default: false

By default, the promisified function will only return the second argument from the callback, which works fine for most APIs. This option can be useful for modules like request that return multiple arguments. Turning this on will make it return an array of all arguments from the callback, excluding the error argument, instead of just the second argument. This also applies to rejections, where it returns an array of all the callback arguments, including the error.

const request = require('request');
const pify = require('pify');

const pRequest = pify(request, {multiArgs: true});

(async () => {
	const [httpResponse, body] = await pRequest('');

Type: Array<string | RegExp>

Methods in a module to promisify. Remaining methods will be left untouched.


Type: Array<string | RegExp>
Default: [/.+(?:Sync|Stream)$/]

Methods in a module not to promisify. Methods with names ending with 'Sync' are excluded by default.


Type: boolean
Default: false

If the given module is a function itself, it will be promisified. Enable this option if you want to promisify only methods of the module.

const pify = require('pify');

function fn() {
	return true;

fn.method = (data, callback) => {
	setImmediate(() => {
		callback(null, data);

(async () => {
	// Promisify methods but not `fn()`.
	const promiseFn = pify(fn, {excludeMain: true});

	if (promiseFn()) {
		console.log(await promiseFn.method('hi'));

Type: boolean
Default: true

Whether the callback has an error as the first argument. You'll want to set this to false if you're dealing with an API that doesn't have an error as the first argument, like fs.exists(), some browser APIs, Chrome Extension APIs, etc.


Type: Function

Custom promise module to use instead of the native one.


How is this different from Node.js's util.promisify?

  • Pify existed long before util.promisify.
  • Pify is faster.
  • Pify supports wrapping a whole module/object, not just a specific method.
  • Pify has useful options like the ability to handle multiple arguments (multiArgs).
  • Pify does not have magic behavior for certain Node.js methods and instead focuses on predictability.

How can I promisify a single class method?

Class methods are not bound, so when they're not called on the class itself, they don't have any context. You can either promisify the whole class or use .bind().

const pify = require('pify');
const SomeClass = require('./some-class');

const someInstance = new SomeClass();

// ❌ `someFunction` can't access its class context.
const someFunction = pify(someClass.someFunction);

// ✅ The whole class is promisified and the `someFunction` method is called on its class.
const someClassPromisified = pify(someClass);

// ✅ `someFunction` is bound to its class before being promisified.
const someFunction = pify(someClass.someFunction.bind(someClass));


  • p-event - Promisify an event by waiting for it to be emitted
  • p-map - Map over promises concurrently
  • More…

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