Fetching & Displaying Data

class DataStore {
  constructor() {
    this.state = new Proxy({}, {
      set: (target, property, value) => {
        target[property] = value;
        this.notifyListeners(property);
        return true;
      }
    });
    this.listeners = new Map();
  }

  subscribe(key, callback) {
    if (!this.listeners.has(key)) {
      this.listeners.set(key, new Set());
    }
    this.listeners.get(key).add(callback);
  }

  notifyListeners(key) {
    if (this.listeners.has(key)) {
      this.listeners.get(key).forEach(callback => callback(this.state[key]));
    }
  }