最近大量的用到jQuery Callbacks 对象，jQuery库中的$.ajax()和$.Deferred() 对象也是基于这个对象实现，中午不困， 利用这点时间片自己动手模拟实现了这个对象的部分功能（没有100%完全测试）， 以加深理解：
用法和$.Callbacks完全一致 ， 但是只是实现了add , remove , fire , empty, has和带参数的构造函数功能， $.Callbacks 还有disable,disabled, fireWith , fired , lock, locked 方法
代码如下：
1 String.prototype.trim = function () 2 { 3 return this.replace( /^\s+|\s+$/g, '' ); 4 }; 5 6 // Simulate jQuery.Callbacks object 7 function MyCallbacks( options ) 8 { 9 var ops = { once: false, memory: false, unique: false, stopOnFalse: false }; 10 11 if ( typeof options === 'string' && options.trim() !== '' ) 12 { 13 var opsArray = options.split( /\s+/ ); 14 for ( var i = 0; i < options.length; i++ ) 15 { 16 if ( opsArray[i] === 'once' ) 17 ops.once = true; 18 else if ( opsArray[i] === 'memory' ) 19 ops.memory = true; 20 else if ( opsArray[i] === 'unique' ) 21 ops.unique = true; 22 else if ( opsArray[i] === 'stopOnFalse' ) 23 ops.stopOnFalse = true; 24 } 25 } 26 27 var ar = []; 28 var lastArgs = null; 29 var firedTimes = 0; 30 31 function hasName( name ) 32 { 33 var h = false; 34 35 if ( typeof name === 'string' 36 && name !== null 37 && name.trim() !== '' 38 && ar.length > 0 ) 39 { 40 for ( var i = 0; i < ar.length; i++ ) 41 { 42 if ( ar[i].name === name ) 43 { 44 h = true; 45 break; 46 } 47 } 48 } 49 50 return h; 51 } 52 53 // add a function 54 this.add = function ( fn ) 55 { 56 if ( typeof fn === 'function' ) 57 { 58 if ( ops.unique ) 59 { 60 // check whether it had been added before 61 if ( fn.name !== '' && hasName( fn.name ) ) 62 { 63 return this; 64 } 65 } 66 67 ar.push( fn ); 68 69 if ( ops.memory ) 70 { 71 // after added , call it immediately 72 fn.call( this, lastArgs ); 73 } 74 } 75 76 return this; 77 }; 78 79 // remove a function 80 this.remove = function ( fn ) 81 { 82 if ( typeof ( fn ) === 'function' 83 && fn.name !== '' 84 && ar.length > 0 ) 85 { 86 for ( var i = 0; i < ar.length; i++ ) 87 { 88 if ( ar[i].name === fn.name ) 89 { 90 ar.splice( i, 1 ); 91 } 92 } 93 } 94 95 return this; 96 }; 97 98 // remove all functions 99 this.empty = function () 100 { 101 ar.length = 0; 102 return this; 103 }; 104 105 // check whether it includes a specific function 106 this.has = function ( fn ) 107 { 108 var f = false; 109 110 if ( typeof ( fn ) === 'function' 111 && fn.name !== '' 112 && ar.length > 0 ) 113 { 114 for ( var i = 0; i < ar.length; i++ ) 115 { 116 if ( ar[i].name === fn.name ) 117 { 118 f = true; 119 break; 120 } 121 } 122 } 123 124 return f; 125 }; 126 127 // invoke funtions it includes one by one 128 this.fire = function ( args ) 129 { 130 if ( ops.once && firedTimes > 0 ) 131 { 132 return this; 133 } 134 135 if ( ar.length > 0 ) 136 { 137 var r; 138 139 for ( var i = 0; i < ar.length; i++ ) 140 { 141 r = ar[i].call( this, args ); 142 143 if ( ops.stopOnFalse && r === false ) 144 { 145 break; 146 } 147 } 148 } 149 150 firedTimes++; 151 152 if ( ops.memory ) 153 { 154 lastArgs = args; 155 } 156 157 return this; 158 }; 159 };
测试函数如下：（注意fn1 fn2是匿名函数， fn2返回false , fn3是有“名”函数）
var fn1 = function ( v ) { console.log( 'fn1 ' + ( v || '' ) ); }; var fn2 = function ( v ) { console.log( 'fn2 ' + ( v || '' ) ); return false; }; function fn3( v ) { console.log( 'fn3 ' + ( v || '' ) ); };
1 . 测试add & fire
var cb=new MyCallbacks();
cb.add(fn1)
cb.add(fn2)
cb.add(fn3)
cb.fire('hello')
输出：
var cb=new MyCallbacks();
cb.add(fn1)
cb.add(fn2)
cb.add(fn3)
cb.has(fn1)
cb.has(fn3)
输出：
false
---------------
true
3.测试带参数的构造函数 : once
var cb=new MyCallbacks('once')
cb.add(fn1)
cb.fire('hello')
cb.fire('hello')
cb.add(fn2)
cb.fire('hello')
输出：
hello
-------------------
------------------
------------------------------
4.测试带参数的构造函数 : memory
var cb=new MyCallbacks('memory')
cb.add(fn1)
cb.fire('hello') // 输出 : fn1 hello
cb.add(fn2) // 输出 : fn2 hello
cb.fire('hello')
输出 :
5.测试带参数的构造函数 : stopOnFalse
var cb=new MyCallbacks('stopOnFalse')
cb.add(fn1)
cb.add(fn2)
cb.add(fn3)
cb.fire('hello')
输出：
6.测试带参数的构造函数 :unique
var cb=new MyCallbacks('unique')
b.add(fn3)
b.add(fn3)
cb.fire('hello')
输出：
fn3 hello
7. 测试带组合参数的构造函数：四个设置参数可以随意组合，一下只测试全部组合的情况， 不然要写16个测试用例 T_T
var cb=new MyCallbacks('once memory unique stopOnFalse')
cb.add(fn1) // 输出： fn1
cb.add(fn2) // 输出： fn2
cb.add(fn3) // 输出： fn3
cb.fire('hello')
输出：
cb.fire('hello') // 输出：没有输出
以下是官方API 文档：
Description: A multi-purpose callbacks list object that provides a powerful way to manage callback lists.The $.Callbacks() function is internally used to provide the base functionality behind the jQuery $.ajax() and$.Deferred() components. It can be used as a similar base to define functionality for new components.
构造函数 ： jQuery.Callbacks( flags )
Possible flags:
once: Ensures the callback list can only be fired once (like a Deferred).memory: Keeps 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: Ensures a callback can only be added once (so there are no duplicates in the list).stopOnFalse: Interrupts callings when a callback returns false.
By default a callback list will act like an event callback list and can be "fired" multiple times.
Two specific methods were being used above: .add() and .fire(). The .add() method supports adding new callbacks to the callback list, while the .fire() method executes the added functions and provides a way to pass arguments to be processed by the callbacks in the same list.
利用Callbacks 实现发布订阅模式 pub/sub: (官方文档)
var topics = {}; 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; };
$.Topic( 'mailArrived' ).subscribe( function ( e ) { console.log( 'Your have new email! ' ); console.log( "mail title : " + e.title ); console.log( "mail content : " + e.content ); } ); $.Topic( 'mailArrived' ).publish( { title: 'mail title', content: 'mail content' } );