为每个匹配的元素设置CSS宽度(width)属性的值。如果没有明确指定单位（如：em或%），使用px。

返回值:jQuery

参数:

• val (String|Number): 要设置的宽度值

示例:

$("p").width(20);

HTML 代码:

<p>This is just a test.</p>

结果:

<p style="width:20px;">This is just a test.</p>

示例:

$("p").width("20em");

HTML 代码:

<p>This is just a test.</p>

结果:

<p style="width:20em;">This is just a test.</p>

Set the CSS width of every matched element. If no explicit unit was specified (like 'em' or '%') then "px" is added to the width.

Return value: jQuery
Parameters:

• val (String|Number): Set the CSS property to the specified value.

Example:

 $("p").width(20);  

Before:

 <p>This is just a test.</p>  

 <p style="width:20px;">This is just a test.</p>

Example:

 $("p").width("20em");  

 <p>This is just a test.</p>  

Result:

 <p style="width:20em;">This is just a test.</p>