Node.js 事件触发器

🌐 The Node.js Event emitter

如果你在浏览器中使用过 JavaScript，你就会知道用户的大部分交互都是通过事件来处理的：鼠标点击、键盘按键、对鼠标移动的响应，等等。

🌐 If you worked with JavaScript in the browser, you know how much of the interaction of the user is handled through events: mouse clicks, keyboard button presses, reacting to mouse movements, and so on.

在后端方面，Node.js 为我们提供了使用 events 模块 构建类似系统的选项。

🌐 On the backend side, Node.js offers us the option to build a similar system using the events module.

这个模块特别提供了 EventEmitter 类，我们将用它来处理我们的事件。

🌐 This module, in particular, offers the EventEmitter class, which we'll use to handle our events.

你使用该方法进行初始化

🌐 You initialize that using

const EventEmitter = require('node:events');

const eventEmitter = new EventEmitter();

这个对象暴露了包括 on 和 emit 方法在内的许多方法。

🌐 This object exposes, among many others, the on and emit methods.

• emit 用于触发一个事件
• on 用于添加一个回调函数，当事件被触发时将执行该函数

例如，让我们创建一个 start 事件，作为提供示例的一部分，我们通过在控制台记录来作出响应：

🌐 For example, let's create a start event, and as a matter of providing a sample, we react to that by just logging to the console:

eventEmitter.on('start', () => {
  console.log('started');
});

当我们跑步时

🌐 When we run

eventEmitter.emit('start');

触发事件处理程序函数，我们得到控制台日志。

🌐 the event handler function is triggered, and we get the console log.

你可以通过将参数作为 emit() 的附加参数传递来传递给事件处理程序：

🌐 You can pass arguments to the event handler by passing them as additional arguments to emit():

eventEmitter.on('start', number => {
  console.log(`started ${number}`);
});

eventEmitter.emit('start', 23);

多个参数：

🌐 Multiple arguments:

eventEmitter.on('start', (start, end) => {
  console.log(`started from ${start} to ${end}`);
});

eventEmitter.emit('start', 1, 100);

EventEmitter 对象还公开了其他几种与事件交互的方法，例如

🌐 The EventEmitter object also exposes several other methods to interact with events, like

• once(): 添加一次性监听器
• removeListener() / off()：从事件中移除事件监听器
• removeAllListeners(): 移除某个事件的所有监听器

你可以在官方文档中阅读有关这些方法的更多信息。

🌐 You can read more about these methods in the official documentation.