addEvent兼容版

function addEvent(elem,type,handle){
        if (elem.addEventlistener)
        {
            elem.addEventlistener(type,handle,false);
        }else if (elem.attachEvent)
        {
            elem.attachEvent('on'+type,function(){
                handle.call(elem);
            });
        }else {
            elem['on'+type] = handle;
        }
}

handle.call(elem);ie9以下支持，但是this指向window，所以把指向改为事件对象