async-as-promised

async-as-promised is a utility module that provides straight-forward, powerful functions for working with Promise based JavaScript.

The functions contained within this module are modeled off the API provided by @caolan's excellent async module. This module is intended to provide a similar API for working with Promise based modules as async provides for callback based modules.

async-as-promised provides over twenty functions that include the usual 'functional' suspects (map, reduce, filter, each…) as well as some common patterns for asynchronous control flow (parallel, series, waterfall…).

Quick Examples

var fs = require('fs');
var async = require('async-as-promised');
var statPromise = async.promisify(fs, fs.stat);
var existsPromise = async.promisify(fs, fs.exists);

async.map(['file1', 'file2', 'file3'], statPromise).then(function (results){
	// results is now an array of stats for each file
});

async.parallel([
	function(){}, // Functions that return promises when called
	function(){},
	function(){}
]).then(function (results){
	// results is an array of the values the provided functions eventually resolved to.
});

async.series([ // Like async.parallel, except each function will be run only after the previous one has resolved
	function(){}, // Functions that return promises when called
	function(){},
	function(){}
]).then(function (results){
	// results is an array of the values the provided functions eventually resolved to.
});

Binding context to a function

This section is really about bind, not about async-as-promised. If you are wondering how to make async-as-promised execute your iterators in a given context, or are confused as to why a method of another library isn't working as an iterator, study this example:

// Here is a simple object with an (unnecessarily roundabout) squaring method
var PromiseSquaringLibrary = {
  squareExponent: 2,
  square: function(number, callback){
    var result = Math.pow(number, this.squareExponent);
    return Promise.resolve(result);
  }
};

async.map([1, 2, 3], PromiseSquaringLibrary.square).then(function (result) {
  // result is [NaN, NaN, NaN]
  // This fails because the `this.squareExponent` expression in the square
  // function is not evaluated in the context of PromiseSquaringLibrary, and is
  // therefore undefined.
});

async.map([1, 2, 3], PromiseSquaringLibrary.square.bind(PromiseSquaringLibrary),).then(function(result) {
  // result is [1, 4, 9]
  // With the help of bind we can attach a context to the iterator before
  // passing it to async. Now the square function will be executed in its
  // 'home' PromiseSquaringLibrary context and the value of `this.squareExponent`
  // will be as expected.
});

Download

The source is available for download from GitHub. Alternatively, you can install using Node package manager (npm):

npm install async-as-promised

Using other Promise Libraries

By default async-as-promised uses the global default Promise object (falling back to promise-polyfill if there is no global Promise object). However async-as-promised supports using any promises/A+ compliant promise library, such as bluebird

To change the Promise library used async-as-promised use the setPromise() method as shown below:

var async = require('async-as-promised');
var bluebird = require('bluebird');

async.setPromise(bluebird);
// async-as-promised will now use bluebird promises for all functions

// to return to the default Promise type simply reset the Promise:
async.resetPromise();