跨平台添加和删除事件—冒泡阶段

var EventUtil = {
        addHandler : function(element,type,handler){
            if (element.addEventListener)//标准
            {
                element.addEventListener(type,handler,false);
            }else if (element.attachEvent)//老IE
            {    //handler,必须保证this指向调用的对象，因为在IE下指向window
                element.attachEvent('on'+type,handler);
            }else {
                element['on'+type] = handler;
            }
        },
        removeHandler : function(element,type,handler){
            if (element.removeEventListener)
            {
                element.removeEventListener(type,handler,false);
            }else if (element.detachEvent)
            {
                element.detachEvent('on'+type,handler);
            }else {
                element['on'+type] = null;
            }
        }
    }