概述 callbacks.lock()
返回值：Callbacks
描述：锁定回调列表的当前状态。
此方法返回绑定它的那个回调对象(this).
如果回调对象被创建，用"memory"标志作为它的参数，绑定函数可能会在回调列表中被锁定后增加并且触发。
示例
用 callbacks.lock()锁定一个回调列表，以避免进一步的修改列表状态 :
// a sample logging function to be added to a callbacks list
var foo = function( value ){
console.log( 'foo:' + value);
}
var callbacks = $.Callbacks();
// add the logging function to the callback list
callbacks.add( foo );
// fire the items on the list, passing an argument
callbacks.fire( 'hello' );
// outputs 'foo: hello'
// lock the callbacks list
callbacks.lock();
// try firing the items again
callbacks.fire( 'world' );
// as the list was locked, no items
// were called so 'world' isn't logged