### 返回值:jQuerymousedown([[data],fn])
### 概述
当鼠标指针移动到元素上方，并按下鼠标按键时，会发生 mousedown 事件。
mousedown 与 click 事件不同，mousedown 事件仅需要按键被按下，而不需要松开即可发生。
### 参数
#### **fn**Function*V1.0*
在每一个匹配元素的mousedown事件中绑定的处理函数。
#### **[data],fn**String,Function*V1.4.3*
**data**:mousedown([Data], fn) 可传入data供函数fn处理。
**fn**:在每一个匹配元素的mousedown事件中绑定的处理函数。
### 示例
#### 描述:
当按下鼠标按钮时，隐藏或显示元素：
##### jQuery 代码:
~~~
$("button").mousedown(function(){
$("p").slideToggle();
});
~~~
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