Question

我一直在抨击为什么我无法捕获Node.js中此代码发出的事件。我的直觉是超出范围，但我无法弄清楚它是什么。 console.log中的index.js代码行永远不会被执行。我的活动没有被发出吗？

player.js

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);
  }
}

module.exports = rocketPlayer

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

你有一些拼写错误：你在听众之后错过了一个支架。您也没有将构造函数参数正确地传递给超级构造函数。以下代码适用于我：

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');

注意：由于您没有定义歌曲，我只是将其转换为字符串

Answer 2

我认为您发布的示例有一些问题;值得注意的是，所写的歌曲方法是抛出异常。

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);

结果：

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

为什么我不能从Node.js中的扩展EventEmitter类中捕获事件？

2 个答案: