An ES6 and Promises/A+ 1.1 fully compliant Promise implementation, that works on IE8+

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0.3.48 years ago9 years agoMinified + gzip package size for core-promise in KB


A promise implementation that is fully conformant to the Promises/A+ spec, passing all the 872 tests from the reference tests, and most of the ES6 tests as well (except a few tests that V8 itself fails). Comes with full TypeScript support. And works from IE8+ without any dependency.

IE8, IE9.. Usage

First you will need to fetch the implementation of the promises via bower:
bower install core-promise
Just include it in the <head> of your page a reference to the core-promise js file:
  <!-- the file is standalone, and has no dependencies -->
  <script type="text/javascript" src="core-promise.js"/>

Usage in Node

The recommended way to use the core-promise is to use the DefaultPromise class, that will use the native Promise class if it is available (e.g. from node 0.12 up).
var Promise = require('core-promise').DefaultPromise,
    CorePromise = require('core-promise').CorePromise;
// ..
// Create new promises with:
var p = new Promise(function(fulfill, reject)) {

Node with TypeScript

If you use TypeScript, then you should know that the core-promise bundles the definition file inside the module. So in order for you to get autocomplete, error checking etc, just add a reference to it, like so:
/// <reference path="node_modules/core-promise/core-promise.d.ts"/>
import core = require("core-promise");
import Promise = core.DefaultPromise;
    .then((x : number) => { // compile error, resolve returns a string

Test Failures

Internet Explorer 9

On IE9 only 2 tests are failing (for strict functions the this comes as the window object instead of undefined - this is a browser bug). Irellevant in practice, since you wouldn't use the this context anyway, because it should be undefined.

Internet Explorer 8

On IE8 multiple tests are failing due to the way the tests themselves are written (calling Object.create, using properties, etc. that the shims are not implementing fully). The core functional tests that do the then() chaining are passing. Note that the implementation of CorePromise itself is compield in pure ES3 JavaScript, and doesn't need any polyfill, and is literally the tests implementation that fails, and not core-promise itself.


On ES6, the tests that fail are a very specific corner case of having inheritance of the Promise, (a broken Promise implementation that inherits another Promise), combined with some illegal calls of executors outside of the Promise. In reality this is irrelevant and can't happen in your production code. Furthermore the native V8 promise implementation also fails these tests. All the other sequence tests in regards with timing, are passing.
  • 2015-09-15 v0.3.4 BugFix Make the DefaultPromise to be of type PromiseConstructor.
  • 2015-09-15 v0.3.3 BugFix Updated the 'main' to point to the right implementation.
  • 2015-09-15 v0.3.2 BugFix CorePromise implements the Promise interface.
  • 2015-09-12 v0.3.1 BugFix Fixed definitions.
  • 2015-09-12 v0.3.0 Use dts-generator. Removed bower support.
  • 2015-07-22 v0.2.3 BugFix Added local.d.ts module file.
  • 2015-07-02 v0.2.2 BugFix Fixed most ES6 tests. Except the ones that V8 itself fails.
  • 2015-07-02 v0.2.1 BugFix Added d.ts module file. Recompiled bower client.
  • 2015-07-01 v0.2.0 ES6 compatible functions added (resolve, all, race, reject).
  • 2015-06-30 v0.1.3 Documentation.
  • 2015-06-30 v0.1.2 BugFix setTimeout call it via () not .call for IE8
  • 2015-06-30 v0.1.1 Browserify browser tests via mocha.
  • 2015-06-30 v0.1.0 Promises/A+ 1.1 compatible.