Async Produce/Consume Channel

channel.js

function channel() {
	const buffer = [];
	const wait = [];
	let lastSignal;
	const consume = function() {
		return buffer.length > 0
			? Promise.resolve(buffer.shift())
			: new Promise((resolve) => {
				wait.push((val) => resolve(val));
			});
	};
	const signal = function() {
		if (wait.length && buffer.length) {
			const next = buffer.shift();
			const waiter = wait.shift();
			waiter(next);
		}
	};
	const produce = function(val) {
		console.log(val);
		lastSignal = val;
		buffer.push(val);
		signal();
	};
	return {
		produce,
		consume,
		getLastSignal: () => lastSignal,
	};
}