Tricky delay function with ES6 yield, inspired by co

delay.js

function run(x, cb) {
	var f;
	if (this.constructor.constructor == (function*() {}).constructor) {
		f = this;
	} else {
		f = x();
	}
	var w = f.next();
	if (!w.done) {
		setTimeout(() => {
			run.call(f, x, cb);
		}, w.value);
	} else {
		cb && cb(w.value);
	}
}

//=======================

run(function *count() {
	console.log(1);
	yield 10;                      // sleep 10ms
	console.log(2);
	yield 1000;                    // sleep 1s
	console.log(3);
	yield 1000;                    // sleep 1s
	return 4;
}, function (res) {
	console.log('result = ', res); // finish
});