How would you do this without:

• exposing the private property of the base class publicly through setters and getters such as in this answer
• or having to duplicate any relevant methods and properties of the base class into the derived class

The properties should remain truly private except within the derived class declaration, so you can't use the protected variable underscore _ convention.

Suppose I have the following code

class CoffeeMachine {
  #waterLimit = 600;
  #waterAmount = 0;

  constructor() {}

  set waterAmount(amount) {
    if (amount < 0) {
      this.#waterAmount = 0;
    } else if (amount > this.#waterLimit) {
      this.#waterAmount = this.#waterLimit;
    } else {
      this.#waterAmount = amount;
    }
  }

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

class TeaMachine extends CoffeeMachine {
  constructor() {
    super();
  }
}

I would like the TeaMachine to be smaller, so I want it's #waterLimit equal to 400 instead of 600

Simply doing the following doesn't work

class TeaMachine extends CoffeeMachine {
  #waterLimit = 400;
  constructor() {
    super();
  }
}

const teaBox = new TeaMachine();
teaBox.waterAmount = 1000;
console.log(teaBox.waterAmount); // 600

This is the closest I could get

The water limit is set on initiation, but is no longer accessible afterwards. Though obviously this is not a perfect solution

class CoffeeMachine {
  #waterLimit;
  #waterAmount = 0;

  constructor(limit = 600) {
    this.#waterLimit = limit;
  }
}

class TeaMachine extends CoffeeMachine {
  constructor() {
    super(400);
  }
}

const teaBox = new TeaMachine();
teaBox.waterAmount = 1000;
console.log(teaBox.waterAmount); // 400

I believe this is possible in Java

Is it even possible to do this in JavaScript while meeting the aforementioned conditions? Or will I have to just accept the restrictions of the language / go down the WeakMap route?