Promises

eric-clapton.js

done = (msg, delay) => {
  console.warn(msg, delay);
  return msg;
}; 

p = (msg, delay) => new Em.RSVP.Promise((resolve) =>  Em.run.later(() => resolve(done(msg, delay)), delay)  );

fast = [p('fast one', 3223), p('fast two',3509)];
slow = [p('slow one', 15523), p('slow two', 15509)];

Em.RSVP.all(slow).then((r) => {
  console.warn(0, r);
  return Em.RSVP.all(fast);
}).then((r) => console.warn(1, r));