Little value wrapper, animation purpose (tracking value changes)

Variable.ts

/**
 * TO BE DISCUSSED.
 * This is a little wrapper that allows to animate any "abstract" variable.
 * Callback may be provided to react on any value change.
 * "old" allows to know the "old" (previous) value.
 */

type Callback = (variable: Variable) => void

export default class Variable {
  #value = 0;

  #old = 0;

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

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

  set value(value: number) {
    this.setValue(value);
  }

  #callback = new Set<Callback>();

  constructor(initialValue: number, callback?: Callback) {
    this.#value = initialValue;
    this.#old = initialValue;
    if (callback !== undefined) {
      this.#callback.add(callback);
    }
  }

  addCallback(callback: Callback) {
    this.#callback.add(callback);
    const unsubscribe = () => this.#callback.delete(callback);
    return unsubscribe;
  }

  setValue(value: number) {
    if (value === this.#value) {
      return;
    }
    this.#old = this.#value;
    this.#value = value;
    this.#callback.forEach((cb) => cb(this));
  }

  goneThrough(threshold: number) {
    return (
      (this.#value >= threshold && this.#old < threshold)
      || (this.#value < threshold && this.#old >= threshold)
    );
  }
}