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.

This implementation is based on then/promise. It has been changed to use the prototype for performance and memory reasons.

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

Downloads

• Promise
• Promise-min

Node

npm install promise-polyfill

Bower

bower install promise-polyfill

Simple use

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"));
  }
});

// Do something when async done
prom.then(function() {
  ...
});

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._setImmediateFn(immedateFn) it will be used instead of window.setTimeout

npm install setasap --save

var Promise = require('promise-polyfill');
var setAsap = require('setasap');
Promise._setImmedateFn(setAsap);

Testing

npm install
npm test

License

MIT