cancelable-promise.js

class Cancelable extends Promise {
  // Symbol.species specifies a function-valued property that the constructor function uses to create derived objects.
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/species
  static get [Symbol.species]() {
    return Promise;
  }
  
  constructor(executor) {
    let _reject;
    super((resolve, reject) => {
      executor(resolve, reject);
      _reject = reject;
    });
    this._reject = _reject;
    this.canceled = false;
  }

  cancel() {
    this.canceled = true;
    this._reject(new Error('Canceled'));
  }
}