play with javascript generators

generators.js

const sleep = ms => new Promise(res => setTimeout(()=>res(ms), ms))

// main1();
//  main2();
// run(main3);
run2(main3);

function main1() {
	console.log(1);
	sleep(100).then(t => console.log(2, t));
	sleep(10).then(t => console.log(3, t));
	console.log(4);
}

async function main2() {
	let t;
	console.log(1);
	t = await sleep(100);
	console.log(2,t);
	t = await sleep(10);
	console.log(3, t);
	console.log(4);
}

function* main3() {
	let t;
	console.log(1);
	t = yield sleep(100);
	console.log(2, t);
	t = yield sleep(10);
	console.log(3, t);
	console.log(4);
}

function run(generator) {
	const iterator = generator();
	
	function iterate (x){
		const it = iterator.next(x);
		if (it.done){
			return;
		}
		it.value.then(iterate);
	}
	
	iterate()
}

function run2(generator) {
	const iterator = generator();

	return iterate(iterator.next())
	
	function iterate (it){
		if (it.done){
			return it.value;
		}
		const promise = it.value;
		return promise.then(x => iterate(iterator.next(x)));
	}
	
}