03.node.js事件类EventEmitter

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1. EventEmitter类
   EventEmitter的核心就是事件触发和事件监听功能的封装.
   支持事件响应的核心模块都是EventEmitter的子类,一般使用子类就可以了.
   EventEmitter的简单例子EventEmitterDemo.js如

   var events = require('events');//引入模块
   //events模块只提供了一个对象events.EventEmitter
   var eventEmitter = new events.EventEmitter();//创建eventEmitter对象
   
   eventEmitter.on('event_name',function(arg1,arg2){//回调参数接收事件参数
       console.log('event_name 1 with two arguments',arg1,arg2);
   });
   
   //为相同事件注册第二个事件监听器
   eventEmitter.on('event_name',function(arg1,arg2,arg3){
       console.log('event_name 2 with three arguments',arg1,arg2,arg3);
   });
   
   //为相同事件注册第三个事件监听器
   eventEmitter.on('event_name',function(){
       console.log('event_name 3 without  argument');
   });
   
   eventEmitter.emit('event_name');//触发事件
   console.log('----------');
   
   setTimeout(function(){
   	eventEmitter.emit('event_name','参数1','参数2');//触发事件,包含事件参数
   
   },1000);
   
   
   

     运行结果
   

   >node EventEmitterDemo.js
   event_name 1 with two arguments undefined undefined
   event_name 2 with three arguments undefined undefined undefined
   event_name 3 without  argument
   ----------
   event_name 1 with two arguments 参数1 参数2
   event_name 2 with three arguments 参数1 参数2 undefined
   event_name 3 without  argument

    
   
   
2. EventEmitter类方法,EventEmitter实例方法与事件
   EventEmitter.js内容如
   

   var events = require('events');
   
   var eventEmitter = new events.EventEmitter();
   /*--------------事件---------------*/
   //EventEmitter内置事件,程序异常触发error事件,没有监听器Node.js输出错误并退出
   //建议为会触发error事件的对象添加监听器,避免整个程序奔溃
   eventEmitter.on('error',function(){
   	console.log('error catched');
   });
   eventEmitter.emit('error');
   //EventEmitter内置事件,eventEmitter实例移除监听器时removeListener事件会被触发
   eventEmitter.on('removeListener',function(event,fn){
   	console.log('remove a Listener',event,fn);
   });
   //EventEmitter内置事件,eventEmitter实例添加新的监听器时newListener事件会被触发
   eventEmitter.on('newListener',function(event,fn){
   	console.log('add new Listener',event,fn);
   });
   
   
   /*--------------类方法----------------*/
   //返回eventEmitter实例指定事件的监听器个数
   var event_name_count = events.EventEmitter.listenerCount(eventEmitter,'event_name');
   var remove_listener_count = events.EventEmitter.listenerCount(eventEmitter,'removeListener');
   console.log('event_name_count:' + event_name_count, 'remove_listener_count:' + remove_listener_count);
   
   /*--------------方法----------------*/
   //单个事件的监听器数量默认为10,超出会有警告信息,可以提高监听器默认限制的数量
   eventEmitter.setMaxListeners(3);
   
   //注册一个监听器
   eventEmitter.on('event_name',function(arg1){
   	console.log('this is a listener added by on with argument',arg1);
   });
   //注册监听器到监听器数组的尾部
   eventEmitter.addListener('event_name',function(arg1,arg2){
   	console.log('this is a listener added by addListener with arguments',arg1,arg2);
   });
   //注册一个单次监听器,被触发后先触发removeListener事件后再执行本监听器,最后移除本监听器
   eventEmitter.once('event_name',function(){
       console.log('this is a listener added by once');
   });
   
   
   var eventHandler = function(){
   	console.log('this is a listener with a name eventHandler');
   };
   eventEmitter.on('event_name',eventHandler);
   
   console.log('------------------event_name事件的监听器数组-------------');
   //返回指定事件的监听器数组
   var eventListenersArray = eventEmitter.listeners('event_name');
   console.log(eventListenersArray);
   
   console.log('-------------------触发event_name事件---------------------');
   //触发监听事件,有监听器返回true,否则返回false
   var hasEventHandler = eventEmitter.emit('event_name','参数1','参数2');
   console.log('hasEventHandler:' + hasEventHandler);
   
   setTimeout(function(){
   	eventEmitter.emit('event_name');
   },1000);
   
   console.log('---------------------------------------------');
   var event_name_count = events.EventEmitter.listenerCount(eventEmitter,'event_name');
   var remove_listener_count = events.EventEmitter.listenerCount(eventEmitter,'removeListener');
   console.log('event_name_count:' + event_name_count, 'remove_listener_count:' + remove_listener_count);
   
   console.log('-----------------移除eventHandler监听器----------------------');
   //移除指定监听器
   eventEmitter.removeListener('event_name',eventHandler);
   
   
   var event_name_count = events.EventEmitter.listenerCount(eventEmitter,'event_name');
   var remove_listener_count = events.EventEmitter.listenerCount(eventEmitter,'removeListener');
   console.log('event_name_count:' + event_name_count, 'remove_listener_count:' + remove_listener_count);
   
   console.log('----------------移除event_name事件所有监听器-------------------');
   //移除指定事件的所有监听器
   eventEmitter.removeAllListeners('event_name');
   var event_name_count = events.EventEmitter.listenerCount(eventEmitter,'event_name');
   var remove_listener_count = events.EventEmitter.listenerCount(eventEmitter,'removeListener');
   console.log('event_name_count:' + event_name_count, 'remove_listener_count:' + remove_listener_count);
   
   console.log('---------------移除eventEmitter实例所有监听器-----------------------');
   //移除所有的监听器
   eventEmitter.removeAllListeners();
   var event_name_count = events.EventEmitter.listenerCount(eventEmitter,'event_name');
   var remove_listener_count = events.EventEmitter.listenerCount(eventEmitter,'removeListener');
   console.log('event_name_count:' + event_name_count, 'remove_listener_count:' + remove_listener_count);
   
   
   
   

    运行结果如
   

   >node EventEmitter.js
   error catched
   event_name_count:0 remove_listener_count:1
   add new Listener event_name function (arg1){
           console.log('this is a listener added by on with argument',arg1);
   }
   add new Listener event_name function (arg1,arg2){
           console.log('this is a listener added by addListener with arguments',ar
   1,arg2);
   }
   add new Listener event_name function (){
       console.log('this is a listener added by once');
   }
   add new Listener event_name function (){
           console.log('this is a listener with a name eventHandler');
   }
   ------------------event_name事件的监听器数组-------------
   [ [Function],
     [Function],
     { [Function: g] listener: [Function] },
     [Function: eventHandler] ]
   -------------------触发event_name事件---------------------
   this is a listener added by on with argument 参数1
   this is a listener added by addListener with arguments 参数1 参数2
   remove a Listener event_name function (){
       console.log('this is a listener added by once');
   }
   this is a listener added by once
   this is a listener with a name eventHandler
   hasEventHandler:true
   ---------------------------------------------
   event_name_count:3 remove_listener_count:1
   -----------------移除eventHandler监听器----------------------
   remove a Listener event_name function (){
           console.log('this is a listener with a name eventHandler');
   }
   event_name_count:2 remove_listener_count:1
   ----------------移除event_name事件所有监听器-------------------
   remove a Listener event_name function (arg1,arg2){
           console.log('this is a listener added by addListener with arguments',ar
   1,arg2);
   }
   remove a Listener event_name function (arg1){
           console.log('this is a listener added by on with argument',arg1);
   }
   event_name_count:0 remove_listener_count:1
   ---------------移除eventEmitter实例所有监听器-----------------------
   remove a Listener error function (){
           console.log('error catched');
   }
   remove a Listener newListener function (event,fn){
           console.log('add new Listener',event,fn);
   }
   event_name_count:0 remove_listener_count:0
   (node:26660) Warning: Possible EventEmitter memory leak detected. 4 event_name
   isteners added. Use emitter.setMaxListeners() to increase limit