node概念笔记之eventemitter

Posted 2020-08-04

1、产生事件分发的对象都是eventemitter的实例

2、events模块只提供一个对象events.EventEmitter,核心就是事件触发和事件监听功能的封装

引入方式　　

//引入events模块
var events = require(‘events‘);
//创建eventEmitter对象
var eventEmitter = new events.EventEmitter();

EventEmitter对象如果在实例化时发生错误，会触发error事件，当添加新的监听器时newListener事件触发，移除时removeListener事件被触发

//event.js文件
var EventEmitter = require(‘events‘).EventEmitter;
var event = new EventEemitter();
event.on(‘some_event‘,function(){
   console.log(‘some_event 事件触发‘) 
});
setTimeOut(function(){
    event.emit(‘some_event‘);
},1000)

一秒后触发some_event，然后监听到这个事件的分发

 

支持若干事件监听器，顺序执行，事件参数作为会掉函数的参数传递

var events = require(‘events‘);
var emitter = new events.EventEmitter();
emitter.on(‘someEvent‘,function(arg1,arg2){
   console.log(‘listener1‘,arg1,arg2); 
});
emitter.on(‘someEvent‘,function(arg1,arg2){
   console.log(‘listener2‘,arg1,arg2); 
});
emitter.emit(‘someEvent‘,arg1,arg2);

下面是是EventEmitter的属性介绍

1、addListener(event,listener)

2、on(event,listener)//回调函数

3、once,单次事件监听，触发后立即解除

4、removeListener

5、removeAllListeners

6、setMaxListeners

7、listeners返回执行事件的监听器数组

8、emit，按参数执行每个监听器

 

实例

var events = require(‘events‘);
var eventEmitter = new events.EventEmitter();

//监听器#1
var listener1 = function listener1(){
  console.log(‘监听器Listener1执行‘)
}
//监听器#2
var listener2 = function listener2(){
  console.log(‘监听器Listener2执行‘)
}
eventEmitter.addListener(‘connect‘,listener1);

eventEmitter.addListener(‘connect‘,listener2);

var eventListeners = require(‘events‘).EventEmitter.EventEmitterCount(eventEmitter,‘connect‘);
console.log(evnetListeners+‘个监听器监听连接事件‘);

eventEmitter.emit(‘connect‘);

// 移除监绑定的 listener1 函数
eventEmitter.removeListener(‘connection‘, listener1);
console.log("listener1 不再受监听。");

// 触发连接事件
eventEmitter.emit(‘connection‘);

eventListeners = require(‘events‘).EventEmitter.listenerCount(eventEmitter,‘connection‘);
console.log(eventListeners + " 个监听器监听连接事件。");

console.log("程序执行完毕。");

 

error事件

继承EventEmitter