async.js

// An example of using yield to simplify the callback hell.
// The limitation is, this only apply to whose callbacks take the normal form of function(err, result), more arguments are ignored.
// Maybe there are many workarounds, but keep it simple, the ECMAScript 6 is around the corner.

// Issues:
// 1. If you yield your syncTask(callback), it will complain that "Generator is already running."
//    An solution is yield setTimeout(callback, 0) in your syncTask(callback).

function Async(task) {
	
	var gen = task(callback);
	
	function callback(err, result) {
		
		if(err) {
			throw err;
		}
		else {
			gen.next(result);
		}
		
	};
	
	gen.next();
	
};

Async(function*(callback) {

	console.log(0);
	// setTimeout's callback require no arguments, !err = true so that the gen.next() will be called.
	yield setTimeout(callback, 1000);
	console.log(1000);
	yield setTimeout(callback, 1000);
	console.log(2000);
	yield setTimeout(callback, 1000);
	console.log(3000);
	return;

});

// ----------------------------------------------------------------
// Ex and Parallel.

function AsyncEx(task) {
	
	var async = {};

	var gen = task(async);
	
	async.times = 0;
	async.currentTimes = 0;
	async.err = null;
	async.results = [];

	async.parallel = function(times) {

		async.times = times;
		async.currentTimes = 0;
		async.err = null;
		async.results = [];

	};

	async.timer = function(result) {

		if(async.times > 0) {

			async.results.push(result);

			async.currentTimes++;

			if(async.currentTimes == async.times) {

				// Dirty reset.
				async.times = 0;
				return async.callbackErrResult(async.err, async.results);

			}
			else {

				return;

			}

		}

	};

	async.endParallel = function() {

	};

	async.callbackResult = function(result) {
		
		if(async.times > 0) {
			async.timer(result);
		}
		else {
			gen.next(result);
		}
		
	};
	
	async.callbackErrResult = function(err, result) {
	
		if(async.times > 0) {

			async.timer(result);

		}
		else {

			if(err) {
				throw err;
			}
			else {
				gen.next(result);
			}
			
		}

	};
	
	gen.next();
	
};
 
AsyncEx(function*(async) {
 
 	async.parallel(3);
	console.log(0);
	setTimeout(async.callbackResult, 1000);
	console.log(1000);
	setTimeout(async.callbackResult, 1000);
	console.log(2000);
	setTimeout(async.callbackResult, 1000);
	console.log(3000);
	var results = yield async.endParallel();
	console.log(results);

	console.log(1);
	yield setTimeout(async.callbackResult, 1000);
	console.log(1000);
	yield setTimeout(async.callbackResult, 1000);
	console.log(2000);
	yield setTimeout(async.callbackResult, 1000);
	console.log(3000);

 	async.parallel(3);
	console.log(2);
	setTimeout(async.callbackResult, 1000);
	console.log(1000);
	setTimeout(async.callbackResult, 1000);
	console.log(2000);
	setTimeout(async.callbackResult, 1000);
	console.log(3000);
	var results = yield async.endParallel();
	console.log(results);

	return;
 
});