node.JS事件機(jī)制說(shuō)明

多數(shù) Node.js 核心 API 都是采用慣用的異步事件驅(qū)動(dòng)架構(gòu)，其中某些類型的對(duì)象（稱為觸發(fā)器）會(huì)周期性地觸發(fā)命名事件來(lái)調(diào)用函數(shù)對(duì)象（監(jiān)聽(tīng)器）。例如，一個(gè)net.Server對(duì)象會(huì)在每次有新連接時(shí)觸發(fā)一個(gè)事件；一個(gè) fs.ReadStream 會(huì)在文件被打開(kāi)時(shí)觸發(fā)一個(gè)事件；一個(gè) stream會(huì)在數(shù)據(jù)可讀時(shí)觸發(fā)事件。

EventEmitter

EventEmitter 類由 events 模塊定義和開(kāi)放的，所有能觸發(fā)事件的對(duì)象都是 EventEmitter 類的實(shí)例

var EventEmitter = require('events');/*{ [Function: EventEmitter] EventEmitter: [Circular], usingDomains: false, defaultMaxListeners: [Getter/Setter], init: [Function], listenerCount: [Function] } */console.log(EventEmitter);

events模塊的EventEmitter屬性指向該模塊本身

var events = require('events');console.log(events.EventEmitter === events);//trueEventEmitter是一個(gè)構(gòu)造函數(shù)，可以用來(lái)生成事件發(fā)生器的實(shí)例emittervar EventEmitter = require('events');var emitter = new EventEmitter();/*EventEmitter { domain: null, _events: {}, _eventsCount: 0, _maxListeners: undefined } */console.log(emitter);

方法

emitter.emit(eventName[, ...args])

eventName <any>

...args <any>

該方法按監(jiān)聽(tīng)器的注冊(cè)順序，同步地調(diào)用每個(gè)注冊(cè)到名為eventName事件的監(jiān)聽(tīng)器，并傳入提供的參數(shù)。如果事件有監(jiān)聽(tīng)器，則返回true，否則返回false

var EventEmitter = require('events');var emitter = new EventEmitter();emitter.on('test1',function(){});console.log(emitter.emit('test1'));//trueconsole.log(emitter.emit('test2'));//false

emitter.on(eventName, listener)

該方法用于添加listener函數(shù)到名為eventName的事件的監(jiān)聽(tīng)器數(shù)組的末尾

eventName <any> 事件名

listener <Function> 回調(diào)函數(shù)

[注意]不會(huì)檢查listener是否已被添加。多次調(diào)用并傳入相同的eventName和listener會(huì)導(dǎo)致listener被添加與調(diào)用多次

var EventEmitter = require('events');var emitter = new EventEmitter();emitter.on('test',function(){  console.log(1);});emitter.on('test',function(){  console.log(2);});emitter.emit('test');//1 2

該方法返回一個(gè) EventEmitter 引用，可以鏈?zhǔn)秸{(diào)用

var EventEmitter = require('events');var emitter = new EventEmitter();emitter.on('test',function(){  console.log(1);}).on('test',function(){  console.log(2);});emitter.emit('test');//1 2

emitter.addListener(eventName, listener)

emitter.on(eventName, listener) 的別名

var EventEmitter = require('events');var emitter = new EventEmitter();emitter.addListener('test',function(){  console.log(1);});emitter.emit('test');//1

emitter.prependListener()

與on()方法不同，prependListener()方法可用于將事件監(jiān)聽(tīng)器添加到監(jiān)聽(tīng)器數(shù)組的開(kāi)頭