Simple callback tracker for changed values

ChangeNotifier.ts

export class ChangeNotifier {
  callbacks: Array<() => void> = [];
  onChange(callback: () => void) {
    this.callbacks.push(callback);
    return () => {
      const index = this.callbacks.indexOf(callback);
      if (index >= 0) {
        this.callbacks.splice(index, 1);
      }
    };
  }
  notify() {
    this.callbacks.forEach((cb) => cb());
  }
}