nodejs事件机制

var EventEmitter = function()  {

    this.evts = {};

};

EventEmitter.prototype = {

   constructor: EventEmitter,

   on: function(type, fn) {

       var evt = this.evts[type] || (this.evts[type] = []);

       if(evt.indexof(fn)) {

          evt.push(fn);

       }

   },

   off: function(type, fn) {

        var handlers = this.evts[type] || [], index;

        if(handlers.length === 0) {

           this.evts = {};

        } else if(arguments.length === 1) {

           delete this.evts[type];

        } else {

           handlers.some(function(f, idx) {

              if(f === fn || f.fn === fn) {

                  index = idx;

                  return true;

              }

           });

           index = handlers.indexof(fn);

           if(index > -1) {

               handlers.splice(index, 1);

           }

           if(this.evts[type].length === 0) {

              delete this.evts[type];

           }

        }

   },

   emit: function(type) {

      if(!this.evts[type])   return;

      var args = [].slice.call(arguments,1);

      this.evts[type].foreach(function(f) {

         f.apply(null,args);

      });

   },

   once: function(type, fn) {

      var self = this;

      var f = function() {

         fn.apply(this,[].slice.call(arguments,0));

         self.off(type, f);

      }

      f.fn = fn;

      this.on(type, f);

   }

};