event事件对象的兼容

var event = {

// 添加事件监听
    add: function(element, type, callback){

if(element.addEventListener){
            element.addEventListener(type, callback, false);
        } else if(element.attachEvent){
            element.attachEvent('on' + type, callback);
        } else {
            element['on' + type] = callback;
        }
    },

// 移除事件监听
    remove: function(element, type, callback){

if(element.removeEventListener){
            element.removeEventListener(type, callback, false);
        } else if(element.detachEvent){
            element.detachEvent('on' + type, callback);
        } else {
            element['on' + type] = null;
        }

    },

//  event 对象
    getEvent: function(event){

return event ? event : window.event;
    },

// 获取目标元素
    getTarget: function(event){

return event.target || event.srcElement;
    },

//   阻止事件的默认行为
    preventDefault: function(event){

if(event.preventDefault){
            event.preventDefault();
        } else {
            event.returnValue = false;
        }
    },

// 阻止冒泡
    stopPropagation: function(){

if(event.stopPropagation){
            event.stopPropagation();
        } else {
            event.cancelBubble = true;
        }
    }

};