用闭包方式实现点击a标签弹也索引值

var self = document.getElementsByTagName("a");

for(var i=0;i<self.length;i++){

    self[i].onclick = (function(i){
        return function(){
            alert(i);
        }
    })(i)

}

<a href="javascript:;">我是老大</a>
<a href="javascript:;">我是老二</a>
<a href="javascript:;">我是老三</a>