t.js

function deferredTimeout(delay) {
    var deferred = new Deferred();
    window.setTimeout(function() {
        deferred.callback({});
    },
    delay);
    return deferred;
}

function yieldToAwait(src) {
	return function () {
		var deferred = new Deferred();
		var generator = src.apply(this, arguments);
		function loop(val) {
			try {
				var ret = generator.send(val);
				ret.then(loop);
			} catch (e if e instanceof StopIteration) {
				deferred.callback();
			}
		}
		loop(undefined);
		return deferred;
	}
}

function a() {
	for (var i = 0; i < 4; ++i) {
		console.log("a"+i);
		yield deferredTimeout(100);
	}
}

var d = yieldToAwait(a)();
d.then(function() { console.log("done") });