const target = { name: "Sarah", age: 25 };

const handler = {
  get(obj, prop) {
    if (prop === 'greeting') {
      return `Hello, I'm ${obj.name}`;
    }
    return obj[prop]?.toString().toUpperCase() || 'UNKNOWN';
  },
  
  set(obj, prop, value) {
    if (typeof value === 'string') {
      obj[prop] = value.toLowerCase();
    } else {
      obj[prop] = value * 2;
    }
    return true;
  }
};

const proxy = new Proxy(target, handler);
console.log(proxy.name);
proxy.city = "Boston";
proxy.score = 15;
console.log(proxy.greeting);
console.log(proxy.city + " " + proxy.score);