var btn= document.getElementById("myBtn"); 
btn.onclick = function{ //具体代码段 }

/*可跨浏览器的事件处理程序
构造EventUtil对象，为其添加可兼容各浏览器的事件处理方法
*/
var EventUtil = {
  /*添加事件处理程序*/
  addHandler: function (element, type, handler) {
    if (element.addEventListener) {
      addEventListener(type, handler, false);
    } else if (element.attachEvent) {
      attachEvent("on" + type, handler);
    } else {
      element["on" + type] = handler;
    }
  },
  /*移除事件处理程序*/
  removeHandler: function (element, type, handler) {
    if (element.removeEventListener) {
      removeEventListener(type, handler, false);
    } else if (element.detachEvent) {
      detachEvent("on" + type, handler);
    } else {
      element["on" + type] = null;
    }
  },
  /*获得事件对象*/
  getEvent: function (event) {
    return event ? event : window.event;
  },
  /*获得事件的目标*/
  getTarget: function (event) {
    return event.target || event.scrElement;
  },
  /*取消事件的默认行为*/
  preventDefault: function (event) {
    if (event.preventDefault) {
      event.preventDefault;
    } else {
      event.returValue = false;
    }
  },
  /*阻止事件进一步冒泡*/
  stopPropagation: function (event) {
    if (event.stopPropagation) {
      event.stopPropagation;
    } else {
      event.cancelBubble = true;
    }
  }
};