Dean Edwards大神写的addEvent库

直接晒代码：

 // written by Dean Edwards, 2005
 // with input from Tino Zijdel, Matthias Miller, Diego Perini

 // http://dean.edwards.name/weblog/2005/10/add-event/

 function addEvent(element, type, handler) {
     if (element.addEventListener) {
         element.addEventListener(type, handler, false);
     } else {
         // assign each event handler a unique ID
         if (!handler.$$guid) handler.$$guid = addEvent.guid++;
         // create a hash table of event types for the element
         if (!element.events) element.events = {};
         // create a hash table of event handlers for each element/event pair
         var handlers = element.events[type];
         if (!handlers) {
             handlers = element.events[type] = {};
             // store the existing event handler (if there is one)
             if (element["on" + type]) {
                 handlers[0] = element["on" + type];
             }
         }
         // store the event handler in the hash table
         handlers[handler.$$guid] = handler;
         // assign a global event handler to do all the work
         element["on" + type] = handleEvent;
     }
 };
 // a counter used to create unique IDs
 addEvent.guid = 1;

 function removeEvent(element, type, handler) {
     if (element.removeEventListener) {
         element.removeEventListener(type, handler, false);
     } else {
         // delete the event handler from the hash table
         if (element.events && element.events[type]) {
             delete element.events[type][handler.$$guid];
         }
     }
 };

 function handleEvent(event) {
     var returnValue = true;
     // grab the event object (IE uses a global event object)
     event = event || fixEvent(((this.ownerDocument || this.document || this).parentWindow || window).event);
     // get a reference to the hash table of event handlers
     var handlers = this.events[event.type];
     // execute each event handler
     for (var i in handlers) {
         this.$$handleEvent = handlers[i];
         if (this.$$handleEvent(event) === false) {
             returnValue = false;
         }
     }
     return returnValue;
 };

 function fixEvent(event) {
     // add W3C standard event methods
     event.preventDefault = fixEvent.preventDefault;
     event.stopPropagation = fixEvent.stopPropagation;
     return event;
 };
 fixEvent.preventDefault = function() {
     this.returnValue = false;
 };
 fixEvent.stopPropagation = function() {
     this.cancelBubble = true;
 };