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：

var swap = function( elem, options, callback ) {
    var ret, name,
        old = {};

    //记住旧的样式，并插入新的样式
    for ( name in options ) {
        old[ name ] = elem.style[ name ];
        elem.style[ name ] = options[ name ];
    }
    
    //执行回调并把指针指向dom元素
    ret = callback.call( elem );

    //恢复旧的样式
    for ( name in options ) {
        elem.style[ name ] = old[ name ];
    }

    return ret;
};

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>

<script>
var swap = function( elem, options, callback ) {
    var ret, name,
        old = {};

    // Remember the old values, and insert the new ones
    for ( name in options ) {
        old[ name ] = elem.style[ name ];
        elem.style[ name ] = options[ name ];
    }

    ret = callback.call( elem );

    // Revert the old values
    for ( name in options ) {
        elem.style[ name ] = old[ name ];
    }

    return ret;
};

var el = document.getElementById('d1');
swap(el,{'display':'block','visibility':'hidden','position':'absolute'},function(){

　　alert(el.offsetWidth); //100

});
</script>