var EventUtil = {
  addHandler : function (element , type, handler {
     if ( element.addEventListener){
        element.addEventListener(type, handler, false);
      }else if ( element.attachEvent) {
        element.attachEvent("on"+type,handler);
      }else {
         element["on" + type] = handler;
      }
    },
  getEvent : function (event){
      return event ? event : window.event;
     },
   preventDefault : function(event){
      if(event.preventDefault){
         event.preventDefault();
      }else{
         event.returnValue = false;
      }
   },
  removeHandsler : 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] = handler;
     }
    }
   stopPropagation : function(event){
      if(event.stopPropagation){
         event.stopPropagation();
      }else {
          event.cancelBubble = true;
      }
    },
   getRelatedTarget : function(event){
      if(event.relatedTarget){
          return event.relatedTarget;
      }else if (event.toElement){
          return event.toElement;
      }else if(event.fromElement){
          return event.fromElement;
      }esle {
          return null;
       }
    },
    getButton : function (event){
       if(document.implementation.hasFeature("MouseEvents" , "2.0")){
          return event.button;
       }else{
           switch(event.button){
             case 0:
             case 1:
             case 3:
             case 5:
             case 7:
               return 0;
             case 2:
             case 6:
               return 2;
             case 4:
               return 1;
            }
        }
     }
} ;

var btn = document.getElementById("myBtn");
var handler = function(){
  alert("Clicked");
};
EventUtil.addHandler(btn , "click", handler);
//略去其他代码
EventUtil.removeHandler(btn, "click", handler);