爲什麼我無法從Node.js中的擴展EventEmitter類捕獲事件？

Question

我一直在抨擊我的頭，因爲我無法捕獲在Node.js中從此代碼發出的事件。我的直覺感覺是有一些超出範圍的，但我無法弄清楚它是什麼。 index.js中的console.log行代碼永遠不會被執行。我的活動沒有被排出？

player.js

index.js

const rocketPlayer = require('./player.js'); 
const player = new rocketPlayer(); 

player.on('nowPlaying', title => { 
    console.log('caught nowPlaying event'); 
}); 

//define a connection 
player.update(connection) 

Answer 1

你有幾個錯字：你缺少你收聽後的支架。您也不會將構造函數參數正確傳遞給超級構造函數。下面的代碼工作對我來說：

const EventEmitter = require('events').EventEmitter; 

class rocketPlayer extends EventEmitter { 
    constructor(options) { 
    super(options); 
    } 

    update(connection) { 
    //do some logic with playlists 
    this.play(connection); 
    } 

    play(connection) { 
    // do some stuff 
    this.emit('nowPlaying', 'song.title'); 
    } 
} 

const player = new rocketPlayer(); 

player.on('nowPlaying', title => { 
    console.log('caught nowPlaying event'); 
}); // <= fixed missing bracket 

//define a connection 
player.update('connection'); 

注：因爲你沒有定義的歌，我只是把它轉換成字符串

Answer 2

我覺得你有一些事情不對您的例子張貼;值得注意的是歌曲方法如同書寫了一個異常。

player.js：

"use strict"; 
let EventEmitter = require('events').EventEmitter; 

class RocketPlayer extends EventEmitter { 
    constructor(options) { 
    super(options); 
    } 

    update(connection) { 
    //do some logic with playlists 
    this.play(connection); 
    } 

    play(song) { 
    // do some stuff 
    this.emit('nowPlaying', song.title); 
    } 
} 

module.exports = RocketPlayer; 

index.js：

const RocketPlayer = require('./player.js'); 
const player = new RocketPlayer(); 

const connection = {title: "Boooboo!"}; 

player.on('nowPlaying', title => { 
    console.log('caught nowPlaying event', title); 
}); 

//define a connection 
player.update(connection); 

結果：

PS D:\Code\data> node -v 
v7.4.0 
PS D:\Code\data> node ./index 
caught nowPlaying event Boooboo!