const user = {
  profile: {
    name: 'Alice',
    settings: {
      notifications: {
        email: true,
        sms: false
      }
    }
  },
  getPreference(type) {
    return this.profile?.settings?.notifications?.[type] ?? 'not configured';
  }
};

const admin = {
  profile: {
    name: 'Admin',
    settings: null
  },
  getPreference: user.getPreference
};

console.log(admin.getPreference('email'));

const companies = [
  { name: 'TechCorp', founded: 2010 },
  { name: 'DataSystems', founded: 2015 },
  { name: 'WebSolutions', founded: 2008 }
];

const activeClients = new WeakSet();

activeClients.add(companies[0]);
activeClients.add(companies[2]);

companies.pop();

const result = [
  activeClients.has(companies[0]),
  activeClients.has(companies[1]),
  typeof activeClients.size
];

console.log(result);

function processConfig(config) {
  const defaults = {
    timeout: 1000,
    retries: 3,
    enabled: false,
    count: 0
  };
  
  const settings = {
    ...defaults,
    ...config
  };
  
  const effectiveTimeout = settings.timeout ?? 500;
  const effectiveRetries = settings.retries ?? 1;
  const effectiveEnabled = settings.enabled ?? true;
  const effectiveCount = settings.count ?? 5;
  
  console.log([effectiveTimeout, effectiveRetries, effectiveEnabled, effectiveCount]);
}

processConfig({ timeout: null, retries: 0, enabled: undefined });

console.log('Start');

setTimeout(() => {
  console.log('Timeout 1');
}, 0);

Promise.resolve().then(() => {
  console.log('Promise 1');
}).then(() => {
  console.log('Promise 2');
});

setTimeout(() => {
  console.log('Timeout 2');
}, 0);

console.log('End');

const a = 9007199254740991n;
const b = 2n;

function performCalculation() {
  const c = a + 1n;
  const d = c / b;
  const e = d * 2n - 1n;
  
  const result = Number(e) === Number(a);
  console.log(result);
}

performCalculation();

const obj = {
  [Symbol('a')]: 'hidden',
  a: 'visible',
  [Symbol.for('b')]: 'registered',
  b: 123
};

const symbol1 = Symbol.for('b');
const symbol2 = Symbol.for('b');

console.log(obj.a + ', ' + 
  obj[Symbol('a')] + ', ' + 
  obj[symbol1] + ', ' + 
  (symbol1 === symbol2));

function* counter() {
  let i = 0;
  while (true) {
    const direction = yield i;
    if (direction === 'up') i += 2;
    else if (direction === 'down') i -= 1;
    else i += 1;
  }
}

const count = counter();
console.log(count.next().value);
console.log(count.next('up').value);
console.log(count.next('down').value);
console.log(count.next().value);