JS获取CSS样式：style、getComputedStyle与currentStyle详解

<!doctype html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="Generator" content="EditPlus®">
    <meta name="Author" content="Yvette Lau">
    <meta name="Keywords" content="关键字">
    <meta name="Description" content="描述">
    <title>Document</title>
    <style>
      #test{
        width:500px;
        height:300px;
        background-color:#CCC;
        float:left;
      }
    </style>
  </head>
  <body>
    <div id = "test"></div>
    <div id = "tag" style = "width:500px; height:300px;background-color:pink;"></div>
  </body>
</html>

<script type = "text/javascript">
  window.onload = function(){
    var test = document.getElementById("test");
    var tag = document.getElementById("tag");

    //CSS样式对象:CSS2Properties{},CSSStyleDeclaration
    console.log(test.style); //火狐返回空对象CSS2Properties{}，谷歌返回空对象CSSStyleDeclaration{} 
    console.log(tag.style); //返回CSS2Properties{width:"500px",height:"300px",background-color:"pink"}
    //element.style获取的是内嵌式的style，如果不是内嵌式，则是一个空对象

    console.log(tag.style.backgroundColor);//pink
    console.log(tag.style['background-color']);//pink
    //获取类似background-color,border-radius,padding-left类似样式的两种写法啊

    console.log(test.currentStyle) //火狐和谷歌为Undefined,IE返回CSS对象
    console.log(window.getComputedStyle(test,null))//谷歌返回CSSStyleDeclaration{……} ，火狐返回CSS2Properties{……}
    console.log(window.getComputedStyle(test))
    //效果同上,但是在Gecko 2.0 (Firefox 4/Thunderbird 3.3/SeaMonkey 2.1) 之前,第二个参数“伪类”是必需的(如果不是伪类,设置为null)

    console.log(test.currentStyle.width);//500px(IE)
    console.log(window.getComputedStyle(test).width); //500px;
    console.log(window.getComputedStyle(test)['width']);//500px;
    //document.defaultView.getComputedStyle(element,null)[attr]/window.getComputedStyle(element,null)[attr]   
  }
</script>

function getStyle(element, attr){
      if(element.currentStyle){
        return element.currentStyle[attr];
      }else{
        return window.getComputedStyle(element,null)[attr];
      }
    }
    console.log(getStyle(test,"cssFloat"));//left
    console.log(getStyle(test,"float"));  //left,早前FF和chrome需要使用cssFloat，不过现在已经不必
    console.log(getStyle(test,"stylefloat"));//火狐和谷歌都是undefined
    console.log(getStyle(test,"styleFloat")); //IE9以下必须使用styleFloat，IE9及以上,支持styleFloat和cssFloat

    console.log(window.getComputedStyle(test).getPropertyValue("float"))