/**

* @author Jeffrey.Deng

* 将按队列执行任务

* 可以队列ajax和普通任务

*/

(function (factory) {

/* global define */

if (typeof define === 'function' && define.amd) {

// AMD. Register as an anonymous module.

define(['jquery'], factory);

} else {

// Browser globals

window.TaskQueue = factory(window.jQuery);

}

})(function ($) {

/* Class: TaskQueue

* Constructor: handler

* takes a function which will be the task handler to be called,

* handler should return Deferred object(not Promise), if not it will run immediately;

* methods: append

* appends a task to the Queue. Queue will only call a task when the previous task has finished

*/

var TaskQueue = function (handler) {

var tasks = [];

// empty resolved deferred object

var deferred = $.when();

// handle the next object

function handleNextTask() {

// if the current deferred task has resolved and there are more tasks

if (deferred.state() == "resolved" && tasks.length > 0) {

// grab a task

var task = tasks.shift();

// set the deferred to be deferred returned from the handler

deferred = handler(task);

// if its not a deferred object then set it to be an empty deferred object

if (!(deferred && deferred.promise)) {

deferred = $.when();

}

// if we have tasks left then handle the next one when the current one

// is done.

if (tasks.length >= 0) {

deferred.done(handleNextTask);

}

}

}

// appends a task.

this.append = function (task) {

// add to the array

tasks.push(task);

// handle the next task

handleNextTask();

};

};

return TaskQueue;

});