// 把所有方法封装到一个对象里面，充分考虑兼容写法
var EventUtil = {
  // 添加DOM事件
  addEvent: function(element, type, handler) {
    if(element.addEventListener) { //DOM2级
      element.addEventListener(type, handler, false);
    }else if(element.attachEvent) {  //IE
      element.attachEvent("on"+ type, handler);
    }else {
      element["on" + type] = handler;
    }
  },
  // 移除DOM事件
  removeEvent: function(element, type, handler) {
    if(element.removeEventListener) { //DOM2级
      element.removeEventListener(type, handler, false);
    }else if(element.detachEvent) {  //IE
      element.detachEvent("on"+ type, handler);
    }else {
      element["on" + type] = null;
    }
  },
  // 阻止事件冒泡
  stopPropagation: function(ev) {
    if(ev.stopPropagation) {
      ev.stopPropagation();
    }else {
      ev.cancelBubble = true;
    }
  },
  // 阻止默认事件
  preventDefault: function(ev) {
    if(ev.preventDefault) {
      ev.preventDefaule();
    }else {
      ev.returnValue = false;
    }
  },
  // 获取事件源对象
  getTarget: function(ev) {
    return event.target || event.srcElement;
  },
  // 获取事件对象
  getEvent: function(e) {
    var ev = e || window.event;
    if(!ev) {
      var c = this.getEvent.caller;
      while(c) {
        ev = c.arguments[0];
        if(ev && Event == ev.constructor) {
          break;
        }
        c = c.caller;
      }
    }
    return ev;
  }
};