Doubling up

[ForbesLindesay]

Do we need to support propagating more progress events than we recieve?

promiseA
  .then(null, null, function (val, prop) { prop(0); prop(1);});

[novemberborn]

That could easily be written as:

var promiseB = promiseA.constructor(function(resolver){
  promiseA.then(resolver.fulfill, resolver.reject, function(val){
    resolver.progress(0);
    resolver.progress(1);
  });
});

And of course libraries could provide a utility methods for that abstraction.

[ForbesLindesay]

True, but that requires breaking your nice clean chain of thens.

[domenic]

The OP idea seems a bit unwise given that you could do setTimeout(prop, 50, 100);