private static subclassing.js

// code which works

class Box {
  #producerStamp;

  constructor(items) {
    this.items = items;
  }

  get producerStamp() {
    return this.#producerStamp;
  }

  static of(...items) {
    const box = new this(items);
    box.#producerStamp = 'made by: ' + this.name;
    return box;
  }

  static from(items) {
    const box = new this(items);
    box.#producerStamp = 'made by: ' + this.name;
    return box;
  }
}


class RedBox extends Box {}

console.log(Box.of(0).producerStamp); // 'made by: Box'

console.log(RedBox.of(0).producerStamp); // 'made by: RedBox'


// reasonable refactoring of that, which doesn't:

class Box {
  #producerStamp;

  constructor(items) {
    this.items = items;
  }

  get producerStamp() {
    return this.#producerStamp;
  }

  static #makeWithStamp(items) {
    const box = new this(items);
    box.#producerStamp = 'made by: ' + this.name;
    return box;
  }

  static of(...items) {
    return this.#makeWithStamp(items);
  }

  static from(items) {
    return this.#makeWithStamp(items);
  }
}


class RedBox extends Box {}

console.log(Box.of(0).producerStamp); // 'made by: Box'

console.log(RedBox.of(0).producerStamp); // throws an error at `this.#makeWithStamp`, complaining that #makeWithStamp is missing on RedBox