[Node][Unit36] 使用 util.inherits 來繼承 EventEmitter 的方法

app.js

// 使用 util.inherits 來繼承 EventEmitter 的方法

const EventEmitter = require('events')
const util = require('util')

function Greetr () {
  // 如果我們想要完整繼承 EventEmitter 中的屬性
  EventEmitter.call(this)
  this.greeting = 'someone greet'
}

// inherits(constructor, superConstructor), 讓 constructor 繼承 superConstructor 
util.inherits(Greetr, EventEmitter)

Greetr.prototype.greet = function () {
  console.log(this.greeting)
  this.emit('greet')
}

const greetr1 = new Greetr()
greetr1.on('greet', function () {
  console.log('Hello world')
})

greetr1.greet()

app2.js

// 在 eventEmitter 中代入參數

const EventEmitter = require('events')
const util = require('util')

function Greetr () {
  this.greeting = 'Hello World!!'
}

// inherits(constructor, superConstructor), 讓 constructor 繼承 superConstructor 
util.inherits(Greetr, EventEmitter)

Greetr.prototype.greet = function (data) {
  console.log(this.greeting)
  this.emit('greet', data)
}

const greetr1 = new Greetr()
greetr1.on('greet', function (data) {
  console.log('Someone greeted' + ': ' + data)
})

greetr1.greet('Nice')

app3.js

'use strict'

const EventEmitter = require('events')
const util = require('util')

class Greetr {
  constructor () {
    EventEmitter.call(this)
    this.greeting = 'someone greet'
  }
  greet () {
    console.log(this.greeting)
    this.emit('greet')
  }
}

util.inherits(Greetr, EventEmitter)

const greetr1 = new Greetr()
greetr1.on('greet', function () {
  console.log('Hello world')
})

greetr1.greet()

call.js

const util = require('util')

function Person (firstName, lastName) {
  this.firstName = firstName || 'Aaron'
  this.lastName = lastName || 'Chen'
}

Person.prototype.greet = function () {
  console.log('Hello, ' + this.firstName + ' ' + this.lastName)
}

function policeMan () {
  console.log('this', this)
  Person.call(this)
  /**
   * 等同於執行了
   * this.firstName = 'Aaron'
   * this.lastName = 'Chen
   */

  this.badgeNumber = '1234'
}



util.inherits(policeMan, Person)
let officer = new policeMan()
console.log('officer', officer)
officer.greet()

由於 `util.inherit(constructor, superConstructor) 只會幫我們繼承 superConstructor.prototype 中的內容，所以如果我們想要完整的繼承，也就是也繼承 superConstructor 中的所有屬性，我們要在 constructor 中去呼叫 superConstructor.call(this)，像這樣：

function constructor () {
    superConstructor.call(this)
    this.firstName = 'Aaron'
}