在类中链接承诺[重复]

Question

我有一堂课，我试图像这样链接承诺：

class Parent {
  constructor() {
    this.driver = []
  }
  test() {
    this.method1()
    .then(this.method2)
    .then(() => {
      console.log('all done', this.driver)
    })
    .catch(err => {
      console.log('Something went wrong', err);
    });
  }
  method1() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        this.driver.push('0');
        resolve();
      },200)
    });
  }
  method2() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        this.driver.push('1');
        resolve();
      },200)
    });
  }
}

let instance = new Parent();
instance.test();

但method2 导致错误

未捕获的类型错误：无法读取未定义的属性“驱动程序”

Answer 1

这是因为您将一个方法传递给then 回调并且this 被重新定义。要让this 指向Parent 的实例，请在then 回调中使用箭头函数。

还有其他方法可以做到这一点，请参阅上一个问题的优秀答案：How to access the correct `this` inside a callback?

带有箭头功能的代码

class Parent {
  constructor() {
    this.driver = []
  }
  test() {
    this.method1()
    .then(() => this.method2())
    .then(() => {
      console.log('all done', this.driver)
    })
    .catch(err => {
      console.log('Something went wrong', err);
    });
  }
  method1() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        this.driver.push('0');
        resolve();
      },200)
    });
  }
  method2() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        this.driver.push('1');
        resolve();
      },200)
    });
  }
}

let instance = new Parent();
instance.test();

Answer 2

当你在这里传递method2时

.then(this.method2)

method2 失去与this 的绑定

试试

.then(x => this.method2(x))

或者

.then(this.method2.bind(this))