pify

Promisify a callback-style function

Install

$ npm install pify

Usage

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

// Promisify a single function
pify(fs.readFile)('package.json', 'utf8').then(data => {
	console.log(JSON.parse(data).name);
	//=> 'pify'
});

// Promisify all methods in a module
pify(fs).readFile('package.json', 'utf8').then(data => {
	console.log(JSON.parse(data).name);
	//=> 'pify'
});

API

pify(input, [options])

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

input

Type: Function Object

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

options

multiArgs

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');

pify(request, {multiArgs: true})('https://sindresorhus.com').then(result => {
	const [httpResponse, body] = result;
});

include

Type: string[] RegExp[]

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

exclude

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

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

excludeMain

Type: boolean
Default: false

If given module is a function itself, it will be promisified. Turn this option on 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);
	});
};

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

if (promiseFn()) {
	promiseFn.method('hi').then(data => {
		console.log(data);
	});
}

errorFirst

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.

promiseModule

Type: Function

Custom promise module to use instead of the native one.

Check out pinkie-promise if you need a tiny promise polyfill.

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