当元素的样式为display:none时获取他的宽高

其实这里可以用一个偷梁换柱的办法，把display:none改为 display:block;visibility:hidden;position:absolute;

在jquery的swap方法中实现了这种效果，我们来看源码：

 1 var swap = function( elem, options, callback ) {
 2     var ret, name,
 3         old = {};
 4 
 5     //记住旧的样式，并插入新的样式
 6     for ( name in options ) {
 7         old[ name ] = elem.style[ name ];
 8         elem.style[ name ] = options[ name ];
 9     }
10     
11     //执行回调并把指针指向dom元素
12     ret = callback.call( elem );
13 
14     //恢复旧的样式
15     for ( name in options ) {
16         elem.style[ name ] = old[ name ];
17     }
18 
19     return ret;
20 };

我们来做个例子试试看：

<style>
#d1{width:100px;height:100px;background:red;display:none;}
</style>

<div id="d1"></div>

 1 <script>
 2 var swap = function( elem, options, callback ) {
 3     var ret, name,
 4         old = {};
 5 
 6     // Remember the old values, and insert the new ones
 7     for ( name in options ) {
 8         old[ name ] = elem.style[ name ];
 9         elem.style[ name ] = options[ name ];
10     }
11 
12     ret = callback.call( elem );
13 
14     // Revert the old values
15     for ( name in options ) {
16         elem.style[ name ] = old[ name ];
17     }
18 
19     return ret;
20 };
21 
22 var el = document.getElementById('d1');
23 swap(el,{'display':'block','visibility':'hidden','position':'absolute'},function(){
24 
25 　　alert(el.offsetWidth); //100
26 
27 });
28 </script>