const handler = {
  get: (target, prop) => {
    if (prop in target) {
      return target[prop] * 2;
    }
    return 100;
  }
};

const nums = new Proxy({ a: 5, b: 10 }, handler);
console.log(nums.a, nums.b, nums.c);

async function fetchData() {
  const promise = new Promise(resolve => {
    setTimeout(() => resolve('first'), 2000);
  });
  
  console.log('start');
  const result = await promise;
  console.log(result);
  console.log('end');
}

fetchData();
const x = 'after';
console.log(x);

function* counter() {
  let count = 1;
  while (true) {
    const reset = yield count;
    count = reset ? 1 : count + 1;
  }
}

const gen = counter();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next(true).value);
console.log(gen.next().value);

const user = {
  profile: {
    name: "Alice",
    settings: null
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

const admin = {
  profile: {
    name: "Admin"
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

console.log(user.getPreferences());
console.log(admin.getPreferences());
console.log(user.profile.extra?.id?.toString());

function Animal(name) {
  this.name = name;
}

Animal.prototype.speak = function() {
  return `${this.name} makes a noise`;
};

function Dog(name) {
  Animal.call(this, name);
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.speak = function() {
  return `${this.name} barks`;
};

const animal = new Animal('Animal');
const dog = new Dog('Rex');

console.log(dog instanceof Animal);

const company = {
  name: 'TechCorp',
  departments: {
    engineering: {
      head: { name: 'Alice', contact: null },
      staff: 50
    },
    marketing: null
  }
};

const engineeringContact = company.departments.engineering.head.contact;
const marketingHead = company.departments.marketing?.head?.name;
const financeStaff = company?.departments?.finance?.staff ?? 'Not available';

console.log(`${engineeringContact} - ${marketingHead} - ${financeStaff}`);

const userMap = new WeakMap();

const user1 = { name: 'Alice' };
const user2 = { name: 'Bob' };

userMap.set(user1, { visits: 10 });
userMap.set(user2, { visits: 5 });

// Later in the code...
const entries = [];
for (const obj of [user1, null, user2]) {
  if (obj !== null && userMap.has(obj)) {
    entries.push(userMap.get(obj).visits);
  }
}

console.log(entries.reduce((sum, visits) => sum + visits, 0));