Go-style channels in Javascript with promises/generators

gistfile1.js

//
// Lame implementation of a channel

function channel() {
	return new Channel();
}

function Channel() {
	this._queue = [];
	this._waiters = [];
}

Channel.prototype.take = function() {

	var _resolve = null;
	var promise = new Promise(function(resolve, reject) {
		_resolve = resolve;
	});

	promise.resolve = _resolve;
	
	this._waiters.push(promise);
	this._drain();

	return promise;

}

Channel.prototype.put = function(item) {
	this._queue.push(item);
	this._drain();
}

Channel.prototype._drain = function() {
	
	if (this._drainRequested) return;
	this._drainRequested = true;

	var self = this;
	setTimeout(function() {
		self._drainRequested = false;
		while (self._queue.length && self._waiters.length) {
			self._waiters.shift().resolve(self._queue.shift());
		}
	}, 0);

}

//
//

function wait(delay) {
	return new Promise(function(resolve) {
		setTimeout(resolve, delay)
	});
}

function engine() {

	var tasks = [];
	var waiting = [];

	function spawn(fn, args, ctx) {
		tasks.push([fn.apply(ctx || null, args), undefined]);
		tick();
	}

	function tick() {
		var task = tasks.shift();
		var result = task[0].next(task[1]);
		if (result.done) {
			// do nothing, task complete
		} else if (result.value && typeof result.value.then === 'function') {
			result.value.then(function(res) {
				tasks.push([task[0], res]);
				tick();
			});
		} else {
			tasks.push(task);
			process.nextTick(tick);
		}
	}

	return spawn;

}

var spawn = engine();

var ch = channel();

spawn(function *() {
	while (true) {
		yield wait(Math.random() * 1000);
		var num = Math.floor(Math.random() * 10);
		for (var i = 0; i < num; ++i) {
			var val = Math.floor(Math.random() * 10);
			console.log("put: " + val);
			ch.put(val);	
		}
	}
});

for (var i = 0; i < 10; ++i) {
	spawn(function *(id) {
		while (true) {
			var val = yield ch.take();
			console.log("[id=" + id + "] take: " + val);
		}
	}, [i]);	
}