es6-promise/lib/es6-promise/polyfill.js

A lightweight library that provides tools for organizing asynchronous code

/*global self*/
import { default as RSVPPromise } from "./promise";
import { isFunction } from "./utils";

export default function polyfill() {
  var local;

  if (typeof global !== 'undefined') {
    local = global;
  } else if (typeof window !== 'undefined' && window.document) {
    local = window;
  } else {
    local = self;
  }

  var es6PromiseSupport =
    "Promise" in local &&
    // Some of these methods are missing from
    // Firefox/Chrome experimental implementations
    "resolve" in local.Promise &&
    "reject" in local.Promise &&
    "all" in local.Promise &&
    "race" in local.Promise &&
    // Older version of the spec had a resolver object
    // as the arg rather than a function
    (function() {
      var resolve;
      new local.Promise(function(r) { resolve = r; });
      return isFunction(resolve);
    }());

  if (!es6PromiseSupport) {
    local.Promise = RSVPPromise;
  }
}