javascript - 无法在 es6 类中设置未定义的属性 'value'

Question

<分区>

Answer 1

当你将this.resolve传递给fn时，你需要bind它到 APromise 实例:

fn(this.resolve.bind(this));

演示:

class APromise {
  constructor(fn) {
    this.state = 'pending';
    this.value = null;
    this.deferred = undefined;
    fn(this.resolve.bind(this));
  }

  resolve(newValue) {
    this.value = newValue; // ERROR HERE
    this.state = 'resolved';
    if (this.deferred) {
      this.handle(this.deferred);
    }
  }

  handle(onResolved) {
    if (this.state == 'pending') {
      this.deferred = onResolved;
    } else {
      onResolved(this.value);
    }
  }

  then(onResolved) {
    this.handle(onResolved);
  }
}

const log = v => {
  console.log(v);
};
const myFun = () => {
  return new APromise(resolve => {
    resolve('Hello World');
  });
};

myFun().then(log);