class EventEmitter {
  constructor() {
    this.events = new Map();
  }
  
  on(event, callback) {
    if (!this.events.has(event)) {
      this.events.set(event, []);
    }
    this.events.get(event).push(callback);
    return this;
  }
  
  emit(event, ...args) {
    const callbacks = this.events.get(event);
    if (callbacks) {
      callbacks.forEach(cb => cb(...args));
    }
    return this;
  }
}

const emitter = new EventEmitter();
emitter.on('test', x => console.log(x * 2))
       .on('test', x => console.log(x + 10))
       .emit('test', 5);

const obj = {
  data: ['x', 'y', 'z'],
  *[Symbol.iterator]() {
    for (let i = this.data.length - 1; i >= 0; i--) {
      yield this.data[i].toUpperCase();
    }
  }
};

const result = [];
for (const item of obj) {
  result.push(item);
  if (result.length === 2) break;
}

console.log(result.join('-'));

const x = 15;
const y = 10;
const z = 3;

const result1 = x & y;
const result2 = x | y;
const result3 = x ^ y;
const result4 = ~x;
const result5 = y << z;
const result6 = y >> 1;

console.log(`${result1},${result2},${result3},${result4},${result5},${result6}`);

const wm = new WeakMap();
let obj1 = { name: 'John' };
let obj2 = { name: 'Jane' };

wm.set(obj1, 'developer');
wm.set(obj2, 'designer');

console.log(wm.get(obj1));
console.log(wm.has(obj2));

obj1 = null;
console.log(wm.get(obj1));

const normalObj = {};
try {
  wm.set('string', 'value');
} catch (e) {
  console.log('error');
}

console.log('start');

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

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

Promise.resolve().then(() => {
  console.log('promise 2');
}).then(() => {
  console.log('promise 3');
});

console.log('end');

const nums = [1, 2, 3];
const obj = { a: 1, b: 2 };
const newObj = { ...obj, b: 3, ...obj };

const arr1 = [4, 5];
const arr2 = [6, 7];
const combined = [...nums, ...arr1, ...arr2];

const [first, ...rest] = combined;
const { a, ...remaining } = newObj;

console.log(newObj.b);
console.log(rest.length);
console.log(remaining.b);

const user = {
  profile: {
    settings: {
      theme: 'dark',
      notifications: null
    }
  }
};

const getNotificationSound = (user) => {
  return user?.profile?.settings?.notifications?.sound ?? 'default';
};

console.log(getNotificationSound(user));
console.log(getNotificationSound(null));
console.log(getNotificationSound({ profile: {} }));

function processData() {
  try {
    console.log('start');
    throw new Error('oops');
    console.log('unreachable');
  } catch (e) {
    console.log('caught');
    return 'error';
  } finally {
    console.log('cleanup');
  }
  console.log('end');
}

const result = processData();
console.log(result);