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Promise Polyfill


Lightweight ES6 Promise polyfill for the browser and node. Adheres closely to the spec. It is a perfect polyfill IE, Firefox or any other browser that does not support native promises.

For API information about Promises, please check out this article HTML5Rocks article.

It is extremely lightweight. < 1kb Gzipped

Browser Support

IE8+, Chrome, Firefox, IOS 4+, Safari 5+, Opera


npm install promise-polyfill --save-exact

Bower Use

bower install promise-polyfill


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Simple use

import Promise from 'promise-polyfill';
// To add to window
if (!window.Promise) {
  window.Promise = Promise;

then you can use like normal Promises

var prom = new Promise(function(resolve, reject) {
  // do a thing, possibly async, then…
  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }  else {
    reject(new Error("It broke"));
prom.then(function(result) {
  // Do something when async done


By default promise-polyfill uses setImmediate, but falls back to setTimeout for executing asynchronously. If a browser does not support setImmediate (IE/Edge are the only browsers with setImmediate), you may see performance issues. Use a setImmediate polyfill to fix this issue. setAsap or setImmediate work well.

If you polyfill window.setImmediate or use Promise._immediateFn = yourImmediateFn it will be used instead of window.setTimeout

npm install setasap --save
var Promise = require('promise-polyfill');
var setAsap = require('setasap');
Promise._immediateFn = setAsap;

Unhandled Rejections

promise-polyfill will warn you about possibly unhandled rejections. It will show a console warning if a Promise is rejected, but no .catch is used. You can change this behavior by doing.

Promise._unhandledRejectionFn = <your reject error handler>;

If you would like to disable unhandled rejection messages. Use a noop like below.

Promise._unhandledRejectionFn = function(rejectError) {};


npm install
npm test