promise.js

// Code from: http://www.html5rocks.com/en/tutorials/es6/promises/

var promise = new Promise(function(resolve, reject) {
  // do a thing, possibly async, then…
  if (true) {
    resolve("Stuff worked!");
  }
  else {
    reject(Error("It broke"));
  }
});

promise.then(function(result) {
  console.log(result); // "Stuff worked!"
}, function(err) {
  console.log(err); // Error: "It broke"
});