jQuery.callbacks(flags) | jQuery API

$.Callbacks( 'stopOnFalse' ):

function fn1( value ){
    console.log( value );
    return false;
}

function fn2( value ){
    fn1("fn2 says:" + value);
    return false;
}

var callbacks = $.Callbacks( "stopOnFalse");
callbacks.add( fn1 );
callbacks.fire( "foo" );
callbacks.add( fn2 );
callbacks.fire( "bar" );
callbacks.remove( fn2 );
callbacks.fire( "foobar" );

/*
output:
foo
bar
foobar
*/

因为$.Callbacks() 支持一个列表的flags而不仅仅是一个，设置几个flags，有一个累积效应，类似“&&”。这意味着它可能结合创建回调名单，unique 和确保如果名单已经触发，将有更多的回调调用最新的触发值 (i.e.$.Callbacks("unique memory")).

$.Callbacks( 'unique memory' ):

function fn1( value ){
    console.log( value );
    return false;
}

function fn2( value ){
    fn1("fn2 says:" + value);
    return false;
}
    
var callbacks = $.Callbacks( "unique memory" );
callbacks.add( fn1 );
callbacks.fire( "foo" );
callbacks.add( fn1 ); // repeat addition
callbacks.add( fn2 );
callbacks.fire( "bar" );
callbacks.add( fn2 );
callbacks.fire( "baz" );
callbacks.remove( fn2 );
callbacks.fire( "foobar" );

/*
output:
foo
fn2 says:foo
bar
fn2 says:bar
baz
fn2 says:baz
foobar
*/

Flag结合体是使用的$.Callbacks()内部的.done() 和 .fail()一个递延容器-它们都使用 $.Callbacks('memory once').

$.Callbacks 方法也可以被分离, 为方便起见应该有一个需要定义简写版本：

var callbacks = $.Callbacks(),
    add = callbacks.add,
    remove = callbacks.remove,
    fire = callbacks.fire;

add( fn1 );
fire( "hello world");
remove( fn1 );

$.Callbacks, $.Deferred and Pub/Sub

pub / sub（ Observer模式）背后的一般思路 是促进应用程序的松散耦合。而比对其他对象的方法调用的单个对象，一个对象，而不是另一个对象的一个特定的任务或活动，并通知当它发生。观察家也被称为订阅者，我们指的出版商（或主体）观察对象。出版商事件发生时通知用户

作为一个组件$.Callbacks()创造能力，它可以实现一个pub / sub系统只使用回调列表。使用$.Callbacks作为主题队列，发布和订阅的主题系统可以实现如下:

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;
};

然后，可以很容易的使用这部分应用程序的发布和订阅感兴趣的事件：

// Subscribers
$.Topic( "mailArrived" ).subscribe( fn1 );
$.Topic( "mailArrived" ).subscribe( fn2 );
$.Topic( "mailSent" ).subscribe( fn1 );

// Publisher
$.Topic( "mailArrived" ).publish( "hello world!" );
$.Topic( "mailSent" ).publish( "woo! mail!" );

// Here, "hello world!" gets pushed to fn1 and fn2
// when the "mailArrived" notification is published
// with "woo! mail!" also being pushed to fn1 when
// the "mailSent" notification is published. 

/*
output:
hello world!
fn2 says: hello world!
woo! mail!
*/

虽然这是有用的，可以采取进一步的实施。使用$.Deferreds,这是可能的，以确保发表者只为用户发布一次特别的任务已经完成（解决）通知。这可能是如何在实践中使用的一些进一步的评论，请参见下面的代码示例：

// subscribe to the mailArrived notification
$.Topic( "mailArrived" ).subscribe( fn1 );

// create a new instance of Deferreds
var dfd = $.Deferred();

// define a new topic (without directly publishing)
var topic = $.Topic( "mailArrived" );

// when the deferred has been resolved, publish a 
// notification to subscribers
dfd.done( topic.publish );

// Here the Deferred is being resolved with a message
// that will be passed back to subscribers. It's possible to
// easily integrate this into a more complex routine
// (eg. waiting on an ajax call to complete) so that
// messages are only published once the task has actually
// finished.
dfd.resolve( "its been published!" );