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));

function outer() {
  let x = 10;
  
  function inner() {
    console.log(x);
    
    if(true) {
      let x = 20;
      console.log(x);
    }
    
    console.log(x);
  }
  
  inner();
}

outer();

const ws = new WeakSet();
const obj1 = { id: 1 };
const obj2 = { id: 2 };

ws.add(obj1);
ws.add(obj2);
ws.delete(obj1);

const obj3 = { id: 2 };

console.log([
  ws.has(obj2),
  ws.has(obj1),
  ws.has(obj3),
  ws.has({ id: 2 })
]);

class Task {
  constructor(name) {
    this.name = name;
  }
  async execute() {
    const result = await Promise.resolve(this.name);
    return { result };
  }
}

const task = new Task('test');
task.execute().then(console.log);

const users = [
  { id: 1, name: 'Alice', age: 25 },
  { id: 2, name: 'Bob', age: 30 },
  { id: 3, name: 'Charlie', age: 35 }
];

const result = users
  .filter(user => user.age > 25)
  .map(user => user.name.toUpperCase())
  .reduce((acc, name) => acc + name[0], '');

console.log(result);