/*原文地址：http://ejohn.org/blog/flexible-javascript-events/*/
　　　　http://blog.csdn.net/qi1271199790/article/details/53458043

     /**

      * [addEvent &&removeEvent description]

      * @param {[obj]}   obj  [绑定事件的对象]

      * @param {str}   type [绑定的事件的名称]

      * @param {Function} fn   [事件触发的回调函数]

      */

     var txt=document.getElementById('txt');

     function addEvent(obj,type,fn){

         if(obj.attachEvent){

             obj['e'+type+fn] = fn;

             obj[type+fn] = function(){

                 obj['e'+type+fn](window.event);

             };

             obj.attachEvent('on'+type,obj[type+fn]);

         }else{

             obj.addEventListener(type,fn,false);

         }

     }

     function removeEvent(obj,type,fn){

         if(obj.detachEvent()){

             obj.detachEvent('on'+type,obj[type+fn]);

             obj[type+fn] = null;

         }else{

             obj.removeEventListener(type,fn,false);

         }

     }