惰性加载函数（js的问题）

var addEvent = function( elem, type, handler ){
        if ( window.addEventListener ){
            return elem.addEventListener( type, handler, false );
 
        }
        if ( window.attachEvent ){
            return elem.attachEvent( 'on' + type, handler );
        }
    };

  var addEvent = function(ele,type,handler){
        if(window.addEventListener){
            addEvent = function(ele,type,handler){
                elem.addEventListener( type, handler, false );
            }
        }
        if(window.attachEvent){
            addEvent = function(ele,type,handler){
                elem.attachEvent( 'on' + type, handler );
            }
        }
        addEvent(ele,type,handler);
    }