Have ideas to improve npm?Join in the discussion! »

    pify
    DefinitelyTyped icon, indicating that this package has TypeScript declarations provided by the separate @types/pify package

    5.0.0 • Public • Published

    pify Build Status

    Promisify a callback-style function

    Install

    $ npm install pify
    

    Usage

    const fs = require('fs');
    const pify = require('pify');
     
    (async () => {
        // Promisify a single function.
        const data = await pify(fs.readFile)('package.json', 'utf8');
        console.log(JSON.parse(data).name);
        //=> 'pify'
     
        // Promisify all methods in a module.
        const data2 = await pify(fs).readFile('package.json', 'utf8');
        console.log(JSON.parse(data2).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

    Type: object

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

    Type: Array<string | RegExp>

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

    exclude

    Type: Array<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 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'));
        }
    })();
    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.

    FAQ

    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.

    Related

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

    Get professional support for 'pify' with a Tidelift subscription
    Tidelift helps make open source sustainable for maintainers while giving companies
    assurances about security, maintenance, and licensing for their dependencies.

    Install

    npm i pify

    DownloadsWeekly Downloads

    52,883,571

    Version

    5.0.0

    License

    MIT

    Unpacked Size

    8.87 kB

    Total Files

    4

    Last publish

    Collaborators

    • avatar