polyfillPromise

A polyfill for Browsers not supporting ECMAScript 6 Promise Tests for existence of a Promise constructor in the browser and if doesn't exist adds a window.Promise which meets the ES6 specification.

Browser support for Promises

 <script src="js/polyFillPromise.js"></script>

Using requirejs

 require(['../polyfillPromise-0.1'], function(Promise) {
var promise = new Promise(function(resolve) {
});
promise.then(function(data){
};
});

Typical Use

 <script>
var mp3='music/test.mp3', player=document.getElementById('audio-player')
data={},
audioPromise = new Promise(function (resolve, reject) {
d3.select('#audioPlayer').on('canplay', function(e) {
player.play();
resolve(data);
}).attr('src', mp3);
});
audioPromise.then(function(data){
// Proceed with the app once the audio is loaded }).catch(function(err){
// handle errors
});
</script>

 <script>
require(['../polyfillPromise-0.1'], function(Promise) {
'use strict';
var promise = new Promise(function(resolve) {
setTimeout(function(){
resolve({hello:'world'});
},1500);
});
promise.then(function(data){
if (console && console.log) {
console.log(data);
}
document.getElementsByTagName("pre"[0].innerHTML=JSON.stringify(data);
});
});
</script>

Promise API

The polyfill supports the following methods of the ES6 Promise API

Methods of the Promise constructor

MDN Promise

Promise.all(iterable)

Returns a promise that resolves when all of the promises in the iterable argument have resolved.

Promise.race(iterable)

Returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.

Promise.reject(reason)

Returns a Promise object that is rejected with the given reason.

Promise.resolve(value)

Returns a Promise object that is resolved with the given value. If the value is a thenable (i.e. has a then method), the returned promise will "follow" that thenable, adopting its eventual state; otherwise the returned promise will be fulfilled with the value.

Methods of an instantiated Promise object

Promise.prototype.catch(onRejected)

Appends a rejection handler callback to the promise, and returns a new promise resolving to the return value of the callback if it is called, or to its original fulfilment value if the promise is instead fulfilled.

Promise.prototype.then(onFulfilled, onRejected)
Promise.prototype.then(onFulfilled)

Appends fulfillment and rejection handlers to the promise, and returns a new promise resolving to the return value of the called handler.

##Test Suite

Polyfill Unit tests
instantiation
✓ should throw error if argument is not a function
✓ should have a constructor with name Promise
✓ should have a methods all, race, resolve and reject
✓ instantiated object should have a methods then and catch
Polyfill Functional tests - Promise methods
resolve() & .then()
✓ then() should receive resolved value
✓ A second then() should receive resolved value
✓ then() should return new Promise
reject() and .catch()
✓ catch() should receive rejected value
✓ A second catch() should receive rejected value
✓ catch() should return new Promise
Promise.race()
✓ .race() should resolve when first Promise resolves
✓ .race() should reject when first Promise rejects
Promise.all()
✓ .all() should resolve when last Promise resolves with array of returned values
✓ .all() should reject when first Promise rejects
Promise.resolve() use cases
✓ Promise.resolve(promise) returns promise
✓ Promise.resolve(thenable) returns Promise that follows thenable
✓ Promise.resolve(value) returns Promise that resolves to value
Promise.reject() ✓ Promise.resolve(value) should return promise that rejects to value