javascript监听事件兼容

	function addEvent(el ,type ,fn){
		if(el.addEventListener){
			el.addEventListener(type,fn,false);
		}else if(el.attachEvent){
			el.attachEvent('on'+type,fn);
		}else{
			el['on'+type] = fn;
		}
	}

    function alertIndex(){
    	alert(2);
    }
    addEvent(ipt[0],'click',function(){
    	alert(1)
    });
    addEvent(ipt[0],'click',alertIndex);