Reaktive Array-Unterklassen mittels Proxy-Traps und Symbol.species

class ObservableArray extends Array {
  static get [Symbol.species]() {
    return Array;
  }
 
  static create(onMutation, ...items) {
    const instance = new ObservableArray(...items);
    return new Proxy(instance, {
      set(target, prop, value, receiver) {
        const res = Reflect.set(target, prop, value, receiver);
        if (typeof prop !== 'symbol' && !isNaN(Number(prop))) {
          onMutation({ type: 'set', index: Number(prop), value });
        }
        return res;
      }
    });
  }
}
 
const list = ObservableArray.create(m => console.log('Mutated:', m), 'a', 'b');
const sub = list.slice(0, 1);
list[2] = 'c';