js中addEventListener与attachEvent兼容

function addEvent(obj,type,fn){     if(obj.addEventListener){ //支持addEventListener 则为W3C        obj.addEventListener(type,fn,false);    }else if(obj.attachEvent){ //支持attachEvent则为IE        obj.attachEvent(('on'+type),function(){            fn.call(obj); //传递this  IE必须通过call传递this        });    }}//使用var fm=document.getElementById('myForm');var user=fm.elements['user'];var content=fm.elements['content'];  addEvent(user,'select',function(){    alert(this.value);});