jQuery在1.5引入了Deferred对象（异步列队），当时它还没有划分为一个模块，放到核心模块中。直到1.52才分割出来。它拥有三个方法:_Deferred， Deferred与when。

出于变量在不同作用域的共用，jQuery实现异步列队时不使用面向对象方式，它把_Deferred当作一个工厂方法，返回一个不透明的函数列队。之所以说不透明，是因为它的状态与元素都以闭包手段保护起来，只能通过列队对象提供的方法进行操作。这几个方法分别是done(添加函数)，resolveWith（指定作用域地执行所有函数），resolve（执行所有函数），isResolved（判定是否已经调用过resolveWith或resolve方法），cancel（中断执行操作）。但_Deferred自始至终都作为一个内部方法，从没有在文档中公开过。

Deferred在1.5是两个_Deferred的合体，但1+1不等于2，它还是做了增强。偷偷爆料，Deferred本来是python世界大名鼎鼎的Twisted框架的东西，由早期七大JS类库中的MochiKit取经回来，最后被dojo继承衣钵。jQuery之所以这样构造Deferred，分明不愿背抄袭的恶名，于是方法改得一塌糊涂，是jQuery命名最差的API，完全不知所云。它还加入当时正在热烈讨论的promise机制。下面是一个比较列表：
dojo jQuery 注解 addBoth then 同时添加正常回调与错误回调 addCallback done 添加正常回调 addErrback fail 添加错误回调 callback done 执行所有正常回调 errback reject 执行所有错误回调 doneWith 在指定作用域下执行所有正常回调，但dojo已经在addCallback上指定好了 rejectWith 在指定作用域下执行所有错误回调，但dojo已经在addErrback上指定好了 promise 返回一个外界不能改变其状态的Deferred对象（外称为Promise对象）
jQuery的when方法用于实现回调的回调，或者说，几个异列列队都执行后才执行另外的一些回调。这些后来的回调也是用done, when, fail添加的，但when返回的这个对象已经添加让用户控制它执行的能力了。因为这时它是种叫Promise的东西，只负责添加回调与让用户窥探其状态。一旦前一段回调都触发了，它就自然进入正常回调列队（deferred ，见Deferred方法的定义）或错误回调列队（failDeferred ）中去。不过我这样讲，对于没有异步编程经验的人来说，肯定听得云里雾里。看实例好了。
复制代码 代码如下:
$.when({aa:1}, {aa:2}).done(function(a,b){
console.log(a.aa)
console.log(b.aa)
});

直接输出1,2。如果是传入两个函数，也是返回两个函数。因此对于普通的数据类型，前面的when有多少个参数，后面的done, fail方法的回调就有多少个参数。
复制代码 代码如下:
function fn(){
return 4;
}
function log(s){
window.console && console.log(s)
}
$.when( { num:1 }, 2, '3', fn() ).done(function(o1, o2, o3, o4){
log(o1.num);
log(o2);
log(o3);
log(o4);
});

如果我们想得到各个异步的结果，我们需要用resolve, resolveWith, reject, rejectWith进行传递它们。
复制代码 代码如下:
var log = function(msg){
window.console && console.log(msg)
}
function asyncThing1(){
var dfd = $.Deferred();
setTimeout(function(){
log('asyncThing1 seems to be done...');
dfd.resolve('1111');
},1000);
return dfd.promise();
}
function asyncThing2(){
var dfd = $.Deferred();
setTimeout(function(){
log('asyncThing2 seems to be done...');
dfd.resolve('222');
},1500);
return dfd.promise();
}
function asyncThing3(){
var dfd = $.Deferred();
setTimeout(function(){
log('asyncThing3 seems to be done...');
dfd.resolve('333');
},2000);
return dfd.promise();
}
/* do it */
$.when( asyncThing1(), asyncThing2(), asyncThing3() ).done(function(res1, res2, res3){
log('all done!');
log(res1 + ', ' + res2 + ', ' + res3);
})

异步列队一开始没什么人用（现在也没有什么人用，概念太抽象了，方法名起得太烂了），于是它只能在内部自产自销。首先被染指的是queue。queue模块是1.4为吸引社区的delay插件，特地从data模块中分化的产物，而data则是从event模块化分出来的。jQuery新模块的诞生总是因为用户对已有API的局限制不满而致。最早的queue模块的源码：
复制代码 代码如下:
jQuery.extend({
queue: function( elem, type, data ) {
if ( !elem ) {
return;
}
type = (type || "fx") + "queue";
var q = jQuery.data( elem, type );
// Speed up dequeue by getting out quickly if this is just a lookup
if ( !data ) {
return q || [];
}
if ( !q || jQuery.isArray(data) ) {
q = jQuery.data( elem, type, jQuery.makeArray(data) );
} else {
q.push( data );
}
return q;
},
dequeue: function( elem, type ) {
type = type || "fx";
var queue = jQuery.queue( elem, type ), fn = queue.shift();
// If the fx queue is dequeued, always remove the progress sentinel
if ( fn === "inprogress" ) {
fn = queue.shift();
}
if ( fn ) {
// Add a progress sentinel to prevent the fx queue from being
// automatically dequeued
if ( type === "fx" ) {
queue.unshift("inprogress");
}
fn.call(elem, function() {
jQuery.dequeue(elem, type);
});
}
}
});
jQuery.fn.extend({
queue: function( type, data ) {
if ( typeof type !== "string" ) {
data = type;
type = "fx";
}
if ( data === undefined ) {
return jQuery.queue( this[0], type );
}
return this.each(function( i, elem ) {
var queue = jQuery.queue( this, type, data );
if ( type === "fx" && queue[0] !== "inprogress" ) {
jQuery.dequeue( this, type );
}
});
},
dequeue: function( type ) {
return this.each(function() {
jQuery.dequeue( this, type );
});
},
// Based off of the plugin by Clint Helfers, with permission.
// http://blindsignals.com/index.php/2009/07/jquery-delay/
delay: function( time, type ) {
time = jQuery.fx ? jQuery.fx.speeds[time] || time : time;
type = type || "fx";
return this.queue( type, function() {
var elem = this;
setTimeout(function() {
jQuery.dequeue( elem, type );
}, time );
});
},
clearQueue: function( type ) {
return this.queue( type || "fx", [] );
}
});

1.6添加了_mark,_unmark，promise。queue是让函数同属一个队伍里面，目的是让动画一个接一个执行。_mark则是让它们各自拥有队伍，并列执行（虽然它们只记录异步列队中已被执行的函数个数）。promise则在这些并发执行的动画执行后才执行另些一些回调（或动画）。
复制代码 代码如下:
(function( jQuery ) {
function handleQueueMarkDefer( elem, type, src ) {
//清空记录deferred个数的字段，函数列队与异步列队
var deferDataKey = type + "defer",
queueDataKey = type + "queue",
markDataKey = type + "mark",
defer = jQuery.data( elem, deferDataKey, undefined, true );
if ( defer &&
( src === "queue" || !jQuery.data( elem, queueDataKey, undefined, true ) ) &&
( src === "mark" || !jQuery.data( elem, markDataKey, undefined, true ) ) ) {
// Give room for hard-coded callbacks to fire first
// and eventually mark/queue something else on the element
setTimeout( function() {
if ( !jQuery.data( elem, queueDataKey, undefined, true ) &&
!jQuery.data( elem, markDataKey, undefined, true ) ) {
jQuery.removeData( elem, deferDataKey, true );
defer.resolve();
}
}, 0 );
}
}
jQuery.extend({
_mark: function( elem, type ) {
if ( elem ) {
type = (type || "fx") + "mark";//创建一个以mark为后缀的字段，用于记录此列队中个数
jQuery.data( elem, type, (jQuery.data(elem,type,undefined,true) || 0) + 1, true );
}
},
_unmark: function( force, elem, type ) {
if ( force !== true ) {
type = elem;
elem = force;
force = false;
}
if ( elem ) {
type = type || "fx";
var key = type + "mark",
//让个数减1，如果第一个参数为true，就强逼减至0
count = force ? 0 : ( (jQuery.data( elem, key, undefined, true) || 1 ) - 1 );
if ( count ) {
jQuery.data( elem, key, count, true );
} else {//如果为0，就移除它
jQuery.removeData( elem, key, true );
handleQueueMarkDefer( elem, type, "mark" );
}
}
},
queue: function( elem, type, data ) {
if ( elem ) {
type = (type || "fx") + "queue";
var q = jQuery.data( elem, type, undefined, true );
// Speed up dequeue by getting out quickly if this is just a lookup
if ( data ) {
if ( !q || jQuery.isArray(data) ) {
q = jQuery.data( elem, type, jQuery.makeArray(data), true );
} else {
q.push( data );
}
}
return q || [];
}
},
dequeue: function( elem, type ) {
type = type || "fx";
var queue = jQuery.queue( elem, type ),
fn = queue.shift(),
defer;
// If the fx queue is dequeued, always remove the progress sentinel
if ( fn === "inprogress" ) {
fn = queue.shift();
}
if ( fn ) {
// Add a progress sentinel to prevent the fx queue from being
// automatically dequeued
if ( type === "fx" ) {
queue.unshift("inprogress");
}
fn.call(elem, function() {
jQuery.dequeue(elem, type);
});
}
if ( !queue.length ) {
jQuery.removeData( elem, type + "queue", true );
handleQueueMarkDefer( elem, type, "queue" );
}
}
});
jQuery.fn.extend({
queue: function( type, data ) {
if ( typeof type !== "string" ) {
data = type;
type = "fx";
}
if ( data === undefined ) {
return jQuery.queue( this[0], type );
}
return this.each(function() {
var queue = jQuery.queue( this, type, data );
if ( type === "fx" && queue[0] !== "inprogress" ) {
jQuery.dequeue( this, type );
}
});
},
dequeue: function( type ) {
return this.each(function() {
jQuery.dequeue( this, type );
});
},
// Based off of the plugin by Clint Helfers, with permission.
// http://blindsignals.com/index.php/2009/07/jquery-delay/
delay: function( time, type ) {
time = jQuery.fx ? jQuery.fx.speeds[time] || time : time;
type = type || "fx";
return this.queue( type, function() {
var elem = this;
setTimeout(function() {
jQuery.dequeue( elem, type );
}, time );
});
},
clearQueue: function( type ) {
return this.queue( type || "fx", [] );
},
//把jQuery对象装进一个异步列队，允许它在一系列动画中再执行之后绑定的回调
promise: function( type, object ) {
if ( typeof type !== "string" ) {
object = type;
type = undefined;
}
type = type || "fx";
var defer = jQuery.Deferred(),
elements = this,
i = elements.length,
count = 1,
deferDataKey = type + "defer",
queueDataKey = type + "queue",
markDataKey = type + "mark";
function resolve() {
if ( !( --count ) ) {
defer.resolveWith( elements, [ elements ] );
}
}
while( i-- ) {
//如果它之前已经使用过unmark, queue等方法，那么我们将生成一个新的Deferred放进缓存系统
if (( tmp = jQuery.data( elements[ i ], deferDataKey, undefined, true ) ||
( jQuery.data( elements[ i ], queueDataKey, undefined, true ) ||
jQuery.data( elements[ i ], markDataKey, undefined, true ) ) &&
jQuery.data( elements[ i ], deferDataKey, jQuery._Deferred(), true ) )) {
count++;
tmp.done( resolve );
}
}
resolve();
return defer.promise();
}
});
})( jQuery );

jQuery.ajax模块也被染指，$.XHR对象，当作HTTPXMLRequest对象的仿造器是由一个Deferred对象与一个_Deferred的对象构成。
复制代码 代码如下:
deferred = jQuery.Deferred(),
completeDeferred = jQuery._Deferred(),
jqXHR ={/**/}
//....
deferred.promise( jqXHR );
jqXHR.success = jqXHR.done;
jqXHR.error = jqXHR.fail;
jqXHR.complete = completeDeferred.done;

jQuery1.7，从deferred模块中分化出callback模块，其实就是之前的_Deferred的增强版，添加去重，锁定，return false时中断执行下一个回调，清空等功能。
复制代码 代码如下:
(function( jQuery ) {
// String to Object flags format cache
var flagsCache = {};
// Convert String-formatted flags into Object-formatted ones and store in cache
function createFlags( flags ) {
var object = flagsCache[ flags ] = {},
i, length;
flags = flags.split( /\s+/ );
for ( i = 0, length = flags.length; i < length; i++ ) {
object[ flags[i] ] = true;
}
return object;
}
/*
* Create a callback list using the following parameters:
*
* flags: an optional list of space-separated flags that will change how
* the callback list behaves
*
* By default a callback list will act like an event callback list and can be
* "fired" multiple times.
*
* Possible flags:
*
* once: will ensure the callback list can only be fired once (like a Deferred)
*
* memory: will keep track of previous values and will call any callback added
* after the list has been fired right away with the latest "memorized"
* values (like a Deferred)
*
* unique: will ensure a callback can only be added once (no duplicate in the list)
*
* stopOnFalse: interrupt callings when a callback returns false
*
*/
jQuery.Callbacks = function( flags ) {
// Convert flags from String-formatted to Object-formatted
// (we check in cache first)
flags = flags ? ( flagsCache[ flags ] || createFlags( flags ) ) : {};
var // Actual callback list
list = [],
// Stack of fire calls for repeatable lists
stack = [],
// Last fire value (for non-forgettable lists)
memory,
// Flag to know if list is currently firing
firing,
// First callback to fire (used internally by add and fireWith)
firingStart,
// End of the loop when firing
firingLength,
// Index of currently firing callback (modified by remove if needed)
firingIndex,
// Add one or several callbacks to the list
add = function( args ) {
var i,
length,
elem,
type,
actual;
for ( i = 0, length = args.length; i < length; i++ ) {
elem = args[ i ];
type = jQuery.type( elem );
if ( type === "array" ) {
// Inspect recursively
add( elem );
} else if ( type === "function" ) {
// Add if not in unique mode and callback is not in
if ( !flags.unique || !self.has( elem ) ) {
list.push( elem );
}
}
}
},
// Fire callbacks
fire = function( context, args ) {
args = args || [];
memory = !flags.memory || [ context, args ];
firing = true;
firingIndex = firingStart || 0;
firingStart = 0;
firingLength = list.length;
for ( ; list && firingIndex < firingLength; firingIndex++ ) {
if ( list[ firingIndex ].apply( context, args ) === false && flags.stopOnFalse ) {
memory = true; // Mark as halted
break;
}
}
firing = false;
if ( list ) {
if ( !flags.once ) {
if ( stack && stack.length ) {
memory = stack.shift();
self.fireWith( memory[ 0 ], memory[ 1 ] );
}
} else if ( memory === true ) {
self.disable();
} else {
list = [];
}
}
},
// Actual Callbacks object
self = {
// Add a callback or a collection of callbacks to the list
add: function() {
if ( list ) {
var length = list.length;
add( arguments );
// Do we need to add the callbacks to the
// current firing batch?
if ( firing ) {
firingLength = list.length;
// With memory, if we're not firing then
// we should call right away, unless previous
// firing was halted (stopOnFalse)
} else if ( memory && memory !== true ) {
firingStart = length;
fire( memory[ 0 ], memory[ 1 ] );
}
}
return this;
},
// Remove a callback from the list
remove: function() {
if ( list ) {
var args = arguments,
argIndex = 0,
argLength = args.length;
for ( ; argIndex < argLength ; argIndex++ ) {
for ( var i = 0; i < list.length; i++ ) {
if ( args[ argIndex ] === list[ i ] ) {
// Handle firingIndex and firingLength
if ( firing ) {
if ( i <= firingLength ) {
firingLength--;
if ( i <= firingIndex ) {
firingIndex--;
}
}
}
// Remove the element
list.splice( i--, 1 );
// If we have some unicity property then
// we only need to do this once
if ( flags.unique ) {
break;
}
}
}
}
}
return this;
},
// Control if a given callback is in the list
has: function( fn ) {
if ( list ) {
var i = 0,
length = list.length;
for ( ; i < length; i++ ) {
if ( fn === list[ i ] ) {
return true;
}
}
}
return false;
},
// Remove all callbacks from the list
empty: function() {
list = [];
return this;
},
// Have the list do nothing anymore
disable: function() {
list = stack = memory = undefined;
return this;
},
// Is it disabled?
disabled: function() {
return !list;
},
// Lock the list in its current state
lock: function() {
stack = undefined;
if ( !memory || memory === true ) {
self.disable();
}
return this;
},
// Is it locked?
locked: function() {
return !stack;
},
// Call all callbacks with the given context and arguments
fireWith: function( context, args ) {
if ( stack ) {
if ( firing ) {
if ( !flags.once ) {
stack.push( [ context, args ] );
}
} else if ( !( flags.once && memory ) ) {
fire( context, args );
}
}
return this;
},
// Call all the callbacks with the given arguments
fire: function() {
self.fireWith( this, arguments );
return this;
},
// To know if the callbacks have already been called at least once
fired: function() {
return !!memory;
}
};
return self;
};
})( jQuery );

这期间有还个小插曲，jQuery团队还想增加一个叫Topic的模块，内置发布者订阅者机制，但这封装太溥了，结果被否决。
复制代码 代码如下:
(function( jQuery ) {
var topics = {},
sliceTopic = [].slice;
jQuery.Topic = function( id ) {
var callbacks,
method,
topic = id && topics[ id ];
if ( !topic ) {
callbacks = jQuery.Callbacks();
topic = {
publish: callbacks.fire,
subscribe: callbacks.add,
unsubscribe: callbacks.remove
};
if ( id ) {
topics[ id ] = topic;
}
}
return topic;
};
jQuery.extend({
subscribe: function( id ) {
var topic = jQuery.Topic( id ),
args = sliceTopic.call( arguments, 1 );
topic.subscribe.apply( topic, args );
return {
topic: topic,
args: args
};
},
unsubscribe: function( id ) {
var topic = id && id.topic || jQuery.Topic( id );
topic.unsubscribe.apply( topic, id && id.args ||
sliceTopic.call( arguments, 1 ) );
},
publish: function( id ) {
var topic = jQuery.Topic( id );
topic.publish.apply( topic, sliceTopic.call( arguments, 1 ) );
}
});
})( jQuery );

虽然把大量代码移动callbacks，但1.7的Deferred却一点没有没变小，它变得更重型，它由三个函数列队组成了。并且返回的是Promise对象，比原来多出了pipe, state, progress, always方法。ajax那边就变成这样：
复制代码 代码如下:
deferred = jQuery.Deferred(),
completeDeferred = jQuery.Callbacks( "once memory" ),
deferred.promise( jqXHR );
jqXHR.success = jqXHR.done;
jqXHR.error = jqXHR.fail;
jqXHR.complete = completeDeferred.add;

queue那边也没变多少。
复制代码 代码如下:
(function( jQuery ) {
function handleQueueMarkDefer( elem, type, src ) {
var deferDataKey = type + "defer",
queueDataKey = type + "queue",
markDataKey = type + "mark",
defer = jQuery._data( elem, deferDataKey );
if ( defer &&
( src === "queue" || !jQuery._data(elem, queueDataKey) ) &&
( src === "mark" || !jQuery._data(elem, markDataKey) ) ) {
// Give room for hard-coded callbacks to fire first
// and eventually mark/queue something else on the element
setTimeout( function() {
if ( !jQuery._data( elem, queueDataKey ) &&
!jQuery._data( elem, markDataKey ) ) {
jQuery.removeData( elem, deferDataKey, true );
defer.fire();
}
}, 0 );
}
}
jQuery.extend({
_mark: function( elem, type ) {
if ( elem ) {
type = ( type || "fx" ) + "mark";
jQuery._data( elem, type, (jQuery._data( elem, type ) || 0) + 1 );
}
},
_unmark: function( force, elem, type ) {
if ( force !== true ) {
type = elem;
elem = force;
force = false;
}
if ( elem ) {
type = type || "fx";
var key = type + "mark",
count = force ? 0 : ( (jQuery._data( elem, key ) || 1) - 1 );
if ( count ) {
jQuery._data( elem, key, count );
} else {
jQuery.removeData( elem, key, true );
handleQueueMarkDefer( elem, type, "mark" );
}
}
},
queue: function( elem, type, data ) {
var q;
if ( elem ) {
type = ( type || "fx" ) + "queue";
q = jQuery._data( elem, type );
// Speed up dequeue by getting out quickly if this is just a lookup
if ( data ) {
if ( !q || jQuery.isArray(data) ) {
q = jQuery._data( elem, type, jQuery.makeArray(data) );
} else {
q.push( data );
}
}
return q || [];
}
},
dequeue: function( elem, type ) {
type = type || "fx";
var queue = jQuery.queue( elem, type ),
fn = queue.shift(),
hooks = {};
// If the fx queue is dequeued, always remove the progress sentinel
if ( fn === "inprogress" ) {
fn = queue.shift();
}
if ( fn ) {
// Add a progress sentinel to prevent the fx queue from being
// automatically dequeued
if ( type === "fx" ) {
queue.unshift( "inprogress" );
}
jQuery._data( elem, type + ".run", hooks );
fn.call( elem, function() {
jQuery.dequeue( elem, type );
}, hooks );
}
if ( !queue.length ) {
jQuery.removeData( elem, type + "queue " + type + ".run", true );
handleQueueMarkDefer( elem, type, "queue" );
}
}
});
jQuery.fn.extend({
queue: function( type, data ) {
var setter = 2;
if ( typeof type !== "string" ) {
data = type;
type = "fx";
setter--;
}
if ( arguments.length < setter ) {
return jQuery.queue( this[0], type );
}
return data === undefined ?
this :
this.each(function() {
var queue = jQuery.queue( this, type, data );
if ( type === "fx" && queue[0] !== "inprogress" ) {
jQuery.dequeue( this, type );
}
});
},
dequeue: function( type ) {
return this.each(function() {
jQuery.dequeue( this, type );
});
},
// Based off of the plugin by Clint Helfers, with permission.
// http://blindsignals.com/index.php/2009/07/jquery-delay/
delay: function( time, type ) {
time = jQuery.fx ? jQuery.fx.speeds[ time ] || time : time;
type = type || "fx";
return this.queue( type, function( next, hooks ) {
var timeout = setTimeout( next, time );
hooks.stop = function() {
clearTimeout( timeout );
};
});
},
clearQueue: function( type ) {
return this.queue( type || "fx", [] );
},
// Get a promise resolved when queues of a certain type
// are emptied (fx is the type by default)
promise: function( type, object ) {
if ( typeof type !== "string" ) {
object = type;
type = undefined;
}
type = type || "fx";
var defer = jQuery.Deferred(),
elements = this,
i = elements.length,
count = 1,
deferDataKey = type + "defer",
queueDataKey = type + "queue",
markDataKey = type + "mark",
tmp;
function resolve() {
if ( !( --count ) ) {
defer.resolveWith( elements, [ elements ] );
}
}
while( i-- ) {
if (( tmp = jQuery.data( elements[ i ], deferDataKey, undefined, true ) ||
( jQuery.data( elements[ i ], queueDataKey, undefined, true ) ||
jQuery.data( elements[ i ], markDataKey, undefined, true ) ) &&
jQuery.data( elements[ i ], deferDataKey, jQuery.Callbacks( "once memory" ), true ) )) {
count++;
tmp.add( resolve );
}
}
resolve();
return defer.promise( object );
}
});
})( jQuery );

这时候，钩子机制其实已经在jQuery内部蔓延起来，1.5是css模块的cssHooks，1.6是属性模块的attrHooks, propHooks, boolHooks, nodeHooks,1.7是事件模块的fixHooks， keyHooks, mouseHooks,1.8是queue模块的_queueHooks，由于_queueHooks，queue终于瘦身了。
复制代码 代码如下:
View Code?//1.8
jQuery.extend({
queue: function( elem, type, data ) {
var queue;
if ( elem ) {
type = ( type || "fx" ) + "queue";
queue = jQuery._data( elem, type );
// Speed up dequeue by getting out quickly if this is just a lookup
if ( data ) {
if ( !queue || jQuery.isArray(data) ) {
queue = jQuery._data( elem, type, jQuery.makeArray(data) );
} else {
queue.push( data );
}
}
return queue || [];
}
},
dequeue: function( elem, type ) {
type = type || "fx";
var queue = jQuery.queue( elem, type ),
fn = queue.shift(),
hooks = jQuery._queueHooks( elem, type ),
next = function() {
jQuery.dequeue( elem, type );
};
// If the fx queue is dequeued, always remove the progress sentinel
if ( fn === "inprogress" ) {
fn = queue.shift();
}
if ( fn ) {
// Add a progress sentinel to prevent the fx queue from being
// automatically dequeued
if ( type === "fx" ) {
queue.unshift( "inprogress" );
}
// clear up the last queue stop function
delete hooks.stop;
fn.call( elem, next, hooks );
}
if ( !queue.length && hooks ) {
hooks.empty.fire();
}
},
// not intended for public consumption - generates a queueHooks object, or returns the current one
_queueHooks: function( elem, type ) {
var key = type + "queueHooks";
return jQuery._data( elem, key ) || jQuery._data( elem, key, {
empty: jQuery.Callbacks("once memory").add(function() {
jQuery.removeData( elem, type + "queue", true );
jQuery.removeData( elem, key, true );
})
});
}
});
jQuery.fn.extend({
queue: function( type, data ) {
var setter = 2;
if ( typeof type !== "string" ) {
data = type;
type = "fx";
setter--;
}
if ( arguments.length < setter ) {
return jQuery.queue( this[0], type );
}
return data === undefined ?
this :
this.each(function() {
var queue = jQuery.queue( this, type, data );
// ensure a hooks for this queue
jQuery._queueHooks( this, type );
if ( type === "fx" && queue[0] !== "inprogress" ) {
jQuery.dequeue( this, type );
}
});
},
dequeue: function( type ) {
return this.each(function() {
jQuery.dequeue( this, type );
});
},
// Based off of the plugin by Clint Helfers, with permission.
// http://blindsignals.com/index.php/2009/07/jquery-delay/
delay: function( time, type ) {
time = jQuery.fx ? jQuery.fx.speeds[ time ] || time : time;
type = type || "fx";
return this.queue( type, function( next, hooks ) {
var timeout = setTimeout( next, time );
hooks.stop = function() {
clearTimeout( timeout );
};
});
},
clearQueue: function( type ) {
return this.queue( type || "fx", [] );
},
// Get a promise resolved when queues of a certain type
// are emptied (fx is the type by default)
promise: function( type, obj ) {
var tmp,
count = 1,
defer = jQuery.Deferred(),
elements = this,
i = this.length,
resolve = function() {
if ( !( --count ) ) {
defer.resolveWith( elements, [ elements ] );
}
};
if ( typeof type !== "string" ) {
obj = type;
type = undefined;
}
type = type || "fx";
while( i-- ) {
if ( (tmp = jQuery._data( elements[ i ], type + "queueHooks" )) && tmp.empty ) {
count++;
tmp.empty.add( resolve );
}
}
resolve();
return defer.promise( obj );
}
});

同时，动画模块迎来了它第三次大重构，它也有一个钩子Tween.propHooks。它多出两个对象，其中Animation返回一个异步列队，Tween 是用于处理单个样式或属性的变化，相当于之前Fx对象。animate被抽空了，它在1.72可是近百行的规模。jQuery通过钩子机制与分化出一些新的对象，将一些巨型方法重构掉。现在非常长的方法只龟缩在节点模块，回调模块。
复制代码 代码如下:
animate: function( prop, speed, easing, callback ) {
var empty = jQuery.isEmptyObject( prop ),
optall = jQuery.speed( speed, easing, callback ),
doAnimation = function() {
// Operate on a copy of prop so per-property easing won't be lost
var anim = Animation( this, jQuery.extend( {}, prop ), optall );
// Empty animations resolve immediately
if ( empty ) {
anim.stop( true );
}
};
return empty || optall.queue === false ?
this.each( doAnimation ) :
this.queue( optall.queue, doAnimation );
},

到目前为止，所有异步的东西都被jQuery改造成异步列队的“子类”或叫“变种”更合适些。如domReady, 动画，AJAX，与执行了promise或delay或各种特效方法之后的jQuery对象。于是所有异步的东西在promise的加护下，像同步那样编写异步程序。