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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 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 Use

npm install promise-polyfill --save-exact

Bower Use

bower install promise-polyfill

CDN Polyfill Use

This will set a global Promise object if the browser doesn't already have window.Promise.

<script src="https://cdn.jsdelivr.net/npm/promise-polyfill@8/dist/polyfill.min.js"></script>

Downloads

Simple use

If you would like to add a global Promise object (Node or Browser) if native Promise doesn't exist (polyfill Promise). Use the method below. This is useful if you are building a website and want to support older browsers. Javascript library authors should NOT use this method.

import 'promise-polyfill/src/polyfill';

If you would like to not affect the global environment (sometimes known as a ponyfill, you can import the base module. This is nice for library authors or people working in environment where you don't want to affect the global environment.

import Promise from 'promise-polyfill';

If using require with Webpack 2+ (rare), you need to specify the default import

var Promise = require('promise-polyfill').default;

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
});

Performance

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

import Promise from 'promise-polyfill/src/polyfill';
import setAsap from '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.

-NOTE: This only works on promise-polyfill Promises. Native Promises do not support this function

Promise._unhandledRejectionFn = <your reject error handler>;

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

Promise._unhandledRejectionFn = function(rejectError) {};

Testing

npm install
npm test

License

MIT