## 返回值:Booleancallbacks.has(callback)

### 概述

确定是否提供的回调列表

### 参数

#### callback V1.7

用来搜索的回调。

### 示例

#### 描述:

用 callbacks.has() 检查是否回调列表中包含一个特定的回调:

##### jQuery 代码:

    // a sample logging function to be added to a callbacks list
    var foo = function( value1, value2 ){
        console.log( 'Received:' + value1 + ',' + value2 );
    }

    // a second function which will not be added to the list
    var bar = function( value1, value2 ){
        console.log( 'foobar');
    }

    var callbacks = $.Callbacks();

    // add the log method to the callbacks list
    callbacks.add( foo );

    // determine which callbacks are in the list

    console.log( callbacks.has( foo ) ); // true
    console.log( callbacks.has( bar ) ); // false