pify

Promisify a callback-style function

Install

$ npm install --save 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'
});

// or promisify all methods in a module

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

API

pify(input, [promiseModule], [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.

promiseModule

Type: function

Custom promise module to use instead of the native one.

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

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.

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

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

include

Type: array of (string|regex)

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

exclude

Type: array of (string|regex)
Default: [/.+Sync$/]

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

excludeMain

Type: boolean
Default: false

By default, if given module is a function itself, this function 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(data, null);
    });
};

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

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

License

MIT © Sindre Sorhus