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1# pify [![Build Status](https://travis-ci.org/sindresorhus/pify.svg?branch=master)](https://travis-ci.org/sindresorhus/pify)
2
3> Promisify a callback-style function
4
5
6## Install
7
8```
9$ npm install --save pify
10```
11
12
13## Usage
14
15```js
16const fs = require('fs');
17const pify = require('pify');
18
19// Promisify a single function
20pify(fs.readFile)('package.json', 'utf8').then(data => {
21	console.log(JSON.parse(data).name);
22	//=> 'pify'
23});
24
25// Promisify all methods in a module
26pify(fs).readFile('package.json', 'utf8').then(data => {
27	console.log(JSON.parse(data).name);
28	//=> 'pify'
29});
30```
31
32
33## API
34
35### pify(input, [options])
36
37Returns a `Promise` wrapped version of the supplied function or module.
38
39#### input
40
41Type: `Function` `Object`
42
43Callback-style function or module whose methods you want to promisify.
44
45#### options
46
47##### multiArgs
48
49Type: `boolean`<br>
50Default: `false`
51
52By 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.
53
54```js
55const request = require('request');
56const pify = require('pify');
57
58pify(request, {multiArgs: true})('https://sindresorhus.com').then(result => {
59	const [httpResponse, body] = result;
60});
61```
62
63##### include
64
65Type: `string[]` `RegExp[]`
66
67Methods in a module to promisify. Remaining methods will be left untouched.
68
69##### exclude
70
71Type: `string[]` `RegExp[]`<br>
72Default: `[/.+(Sync|Stream)$/]`
73
74Methods in a module **not** to promisify. Methods with names ending with `'Sync'` are excluded by default.
75
76##### excludeMain
77
78Type: `boolean`<br>
79Default: `false`
80
81If given module is a function itself, it will be promisified. Turn this option on if you want to promisify only methods of the module.
82
83```js
84const pify = require('pify');
85
86function fn() {
87	return true;
88}
89
90fn.method = (data, callback) => {
91	setImmediate(() => {
92		callback(null, data);
93	});
94};
95
96// Promisify methods but not `fn()`
97const promiseFn = pify(fn, {excludeMain: true});
98
99if (promiseFn()) {
100	promiseFn.method('hi').then(data => {
101		console.log(data);
102	});
103}
104```
105
106##### errorFirst
107
108Type: `boolean`<br>
109Default: `true`
110
111Whether 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.
112
113##### promiseModule
114
115Type: `Function`
116
117Custom promise module to use instead of the native one.
118
119Check out [`pinkie-promise`](https://github.com/floatdrop/pinkie-promise) if you need a tiny promise polyfill.
120
121
122## Related
123
124- [p-event](https://github.com/sindresorhus/p-event) - Promisify an event by waiting for it to be emitted
125- [p-map](https://github.com/sindresorhus/p-map) - Map over promises concurrently
126- [More…](https://github.com/sindresorhus/promise-fun)
127
128
129## License
130
131MIT © [Sindre Sorhus](https://sindresorhus.com)
132