JavaScript

type User = {
  id: number;
  name: string;
  email?: string;
};

function processUser<T extends User>(user: T): T & { processed: boolean } {
  return { ...user, processed: true };
}

const partialUser = { id: 1, name: 'Alice' };
const result = processUser(partialUser);

console.log(typeof result.email);

function processUserData(data) {
  const settings = {
    theme: data.preferences?.theme ?? 'light',
    notifications: data.preferences?.notifications ?? true,
    fontSize: data.preferences?.fontSize ?? 16
  };
  
  let status = data.status ?? 'active';
  let reputation = data.reputation ?? 0;
  
  console.log(reputation || 'No reputation yet');
  return settings;
}

processUserData({ status: '', reputation: 0 });

function processConfig(config) {
  const defaultPort = 8080;
  const defaultTimeout = 5000;
  
  const port = config?.port ?? defaultPort;
  const timeout = config?.timeout ?? defaultTimeout;
  const debug = config?.debug ?? false;
  
  return { 
    summary: `Port: ${port}, Timeout: ${timeout}, Debug: ${debug ? 'enabled' : 'disabled'}`,
    isUsingDefaults: port === defaultPort && timeout === defaultTimeout
  };
}

const result = processConfig({ port: 0, timeout: null });
console.log(result.summary);

// What will be logged when this code runs?
const counter = (() => {
  let count = 0;
  
  return {
    increment() {
      count += 1;
      return this;
    },
    reset() {
      count = 0;
      return this;
    },
    get value() {
      return count;
    }
  };
})();

const { increment, value } = counter;

increment();
counter.increment();

console.log(value);

function createCounter() {
  let count = 0;
  
  return function() {
    count++;
    return count;
  };
}

const counter1 = createCounter();
const counter2 = createCounter();

counter1();
counter1();
counter2();

const result = counter1() + counter2();
console.log(result);

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

const symbols = Object.getOwnPropertySymbols(obj);
const keys = Object.keys(obj);
const allProps = Reflect.ownKeys(obj);

console.log(symbols.length, keys.length, allProps.length);

const p1 = Promise.resolve(1);
const p2 = new Promise(resolve => resolve(2));
const p3 = new Promise(resolve => setTimeout(() => resolve(3), 0));
const p4 = Promise.reject(4).catch(err => err);

Promise.all([p1, p2, p3, p4])
  .then(values => {
    const result = values.reduce((acc, val) => {
      return acc + val;
    }, 0);
    console.log(result);
  })
  .catch(err => console.log('Error:', err));