Experimenting ES6 Async = Generator + Promise

function getFile(file) {
	return new Promise(
		(resolve,reject) => {
			if (Math.random()>0.3) fakeAjax(file,resolve);
			else reject('SOMETHING GO WRONG WITH '+file);
		}
	);
}

function Async(gen){
	const it = gen(); //get iteretor from Genereator
	return step(Promise.resolve(it.next())); //start "state machine" step into 1st yield gen
	
	function step(p){ 
		//here P is a promise that is resolved with then value of then next iteration it.next()->{value:Promise done:boolean}
		return p.then(s => { //s: {done: boolean, value: Promise}
			if (s.done) return s.value; //if iteretor finish, stop recursion and return last value returned 
			//else use s.value (that is a promise yielded in the gen) and get the value out of the promise (r) and push back r to the itererator 
			return step(s.value.then(r => it.next(r) // (send r-> result of yield in the iterator) and recursive advance another step
						,e => it.throw(e) )); // (if promise has error propagate to generator)
		});
	}
}

function* Run(){
	var p1 = getFile("file1");
	var p2 = getFile("file2");
	var p3 = getFile("file3");

	output (  yield p1  );
	output (  yield p2  );
	output (  yield p3  );
	return "Complete Run request Parallel, print in Sequence!";
}

//RUN PARALLEL REQUEST, SEQUENTIAL PRINT
Async(Run).then(output).catch(showerr);

// **************************************

function fakeAjax(url,cb) {
	var fake_responses = {
		"file1": "The first text",
		"file2": "The middle text",
		"file3": "The last text"
	};
	var randomDelay = (Math.round(Math.random() * 1E4) % 8000) + 1000;

	console.log("Requesting: " + url);

	setTimeout(function(){
		cb(fake_responses[url]);
	},randomDelay);
}

function output(text) {
	console.log(text);
}

function showerr(err) {
	console.error(err);
}