sync.js

/*** 
 *   Sync  
 *
 *     addTask,  addCirle,  addListener,  finish  
 *
 */
(function() {

	var MAX_TOTAL = Math.pow(2, 31);

	function Sync(delay) {
		this.delay = delay;
		this.queue = [];			// 
		this.listeners = [];			//listeners
		this.timer = 0;
		this.count = 0;				// 
	}

	Sync.prototype.setDelay = function(delay) {
		this.delay = delay;
		return this;
	}

	Sync.prototype.addListener = function(func) {
		this.listeners.push(func);
		return this;
	}

	Sync.prototype.removeListener = function(func) {
		var pos = this.listeners.indexOf(func)
		if (pos != -1) {
			this.listeners.splice(pos);
		}
		return this;
	}

	Sync.prototype.addTask = function(func, callback) {
		this.addCircle(1, func, callback);
		return this;
	}

	Sync.prototype.addParallelTask = function(/** func1, func2, func3...  **/) {
		this.addCircle(1, function(index) {
			for(var i = 0; i < arguments.length; i++) {
				var func = arguments[i];
				func(index);
			}
		});
		return this;
	}

	Sync.prototype.addCircle = function(total, func, callback) {
		if (typeof(total) == 'function') {
			func = total;
			total = MAX_TOTAL;
		}
		this.queue.push({
			func : func, 
			total : total,
			index : 0,
			callback : callback
		});
		this.checkStart();
		return this;
	}

	Sync.prototype.checkStart = function(total, func) {
		if (this.timer) {
			return;
		}
		var that = this;
		this.timer = setTimeout(function() {
			var task = that.queue[0];
			if (!task) {
				that.timer = 0;
				return ;
			}
			var ret = that._execute(task, task.index);
			if (ret === true || ++task.index >= task.total) {
				that.queue.shift();
				that._callback(task);
			}
			that.timer = setTimeout(arguments.callee, that.delay);			
		}, this.delay);
	}

	Sync.prototype._execute = function(task, index) {
		var ret = task.func(index);
		for(var i = 0; i < this.listeners.length; i++) {
			this.listeners[i](this.count++);
		}
	}

	Sync.prototype._callback = function(task) {
		task.callback && task.callback(index);
	}

	Sync.prototype.finish = function(bool) {
		if (this.timer) {
			clearTimeout(this.timer);
			this.timer = 0;
		}
		if (bool === undefined || bool === true) {
			for(var i = 0; i < this.queue.length; i++) {
				var task = this.queue[i];
				for(var j = task.index; j < task.total; j++) {
					var ret = this._execute(task, j);
					if (ret === true) {
						break;
					}
				}
				
			}
		}
		this.queue = [];
	}


	window.Sync = Sync;


})();

<script src="sync.js"></script>
<script>

	var a = new Sync(1000);
	a.addListener(function(n){console.log('notify .' + n)});
	a.addCircle(2, function(n) {console.log('execute 2 -- ' + n)});
	a.addCircle(4, function(n) {console.log('execute 4 -- ' + n)});
	a.addCircle(8, function(n) {console.log('execute 8 -- ' + n)});
	setTimeout(function() {
		a.addCircle(function(n) {console.log('execute n -- ' + n)});
		setTimeout(function() {
			a.finish();
		}, 3000);
	}, 3000);

</script>