<style>
        *{
            margin:0;
            padding:0;
        }
        div{
            width:300px;
            height:50px;
            margin:20px;
        }
        .activeColor{
            background: orange;
            
        }
        .odd-color{
            background:#ccc;
        }
        .even-color{
            background: #eee;
        }
</style>
<script>
window.onload=function(){
           var aDiv=document.getElementsByTagName("div"),
               oldColor=" ";
           for(var i=0,len=aDiv.length;i<len;i++){
               if(i%2==0){
                   aDiv[i].className="even-color";
               }else{
                   aDiv[i].className="odd-color";
               }
            aDiv[i].onmouseover=function(){
                 oldColor=this.className;//存储原始颜色
                 this.className="activeColor";//变成激活颜色
            }
            aDiv[i].onmouseout=function(){
                this.className=oldColor;//变成原始颜色
            }
           }
}

</script>
</head>
<body>
     <div>1</div>
     <div>2</div>
     <div>3</div>
     <div>4</div>
     <div>5</div>
     <div>6</div>
</body>
</html>