当一个函数中有两个类时会出现这个问题

Question

我在一个函数中有两个类，由于某种原因，第二个函数this没有被正确识别。类是Emitter和Receiver。我试图弄清楚为什么this这里没有被正确拾取。该日志包含在以下代码中：const chat = (messages) => {  class Emitter {    constructor(messages = []) {      this.messages = messages;      this.event = () => {};    }    setEvent(fn) {      this.event = fn;    }    trigger() {      this.messages.forEach(message => this.event(message));    }  }  class Receiver {    constructor() {      this.messages = [];      // this prints correctly here      ---> Receiver { messages: [] }      console.log('this  ===> ', this)    }    ping(message) {      console.log('this ===>', this)      // this here prints the following      this ===> Emitter {        messages: [ 'Hi', 'Hola', 'Bonjour', 'Hi' ],        event: [Function: ping] }          this.messages.push(message);       }  }  const myReceiver = new Receiver();  const myEmitter = new Emitter(messages);  myEmitter.setEvent(myReceiver.ping);  myEmitter.trigger();  return myReceiver.messages;};

Answer 1

this取决于调用它的范围，而不是定义它的范围 。https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this 在调用 myEmitter.setEvent(myReceiver.ping) 时，只有函数 ping 被传递给 myEmitter，而不是它的作用域我的收件人。如果您想传递 myRevciever 范围，可以将其绑定到函数调用。

myEmitter.setEvent(myReceiver.ping.bind(myReceiver));