javascript - 'this' 在子类中未定义

Question

我不能在快速 route 使用“this”。这是为什么？因为我在B类的多个方法中需要this.postRepo。有什么替代方法吗？

// Parent
export default abstract class A {
  // no constructor
  // few methods
}

// Child
export default class B extends A {
  public postRepo: number

  constructor() {
    super();
    this.postRepo = 111;
  }

  public methodA(req?: Request, res?: Response): any {
    console.log(this); // undefined
    console.log(this.postRepo); // TypeError: Cannot read property 'postRepo' of undefined
  }

  // ...methods that required this.postRepo
}

// New
const classB = new B();
classB.methodA(); // <--- this is working
router.get("/", classB.methodA); // <--- undefined

Answer 1

我以为方法正在失去它的上下文。如果是这样，你可以用箭头函数替换方法，它们的上下文是稳定的:

public methodA = (req?: Request, res?: Response) => {
    console.log(this); // undefined
    console.log(this.postRepo); // TypeError: Cannot read property 'postRepo' of undefined
  }