const user = {
  name: 'John',
  greet() {
    const getName = () => {
      console.log(this.name);
    };
    getName();
  },
  farewell: function() {
    function getName() {
      console.log(this.name);
    }
    getName();
  }
};

user.greet();
user.farewell();

const arr = [1, 2, 3, 4, 5];
const result = arr
  .map(x => x * 2)
  .filter(x => x > 5)
  .reduce((acc, val) => {
    return acc + (val % 3 === 0 ? val : 0);
  }, 0);

console.log(result);

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

items.add(obj1);
items.add(obj2);

obj2.value = 'test';
console.log(items.has(obj2));

obj2 = null;
setTimeout(() => {
  console.log(items.has(obj2));
}, 0);

function* range(start, end) {
  let current = start;
  while (current <= end) {
    if (current % 3 === 0) {
      current++;
      continue;
    }
    yield current++;
  }
}

const gen = range(4, 10);
const result = [...gen];
console.log(result);

async function demo() {
  console.log('1');
  
  setTimeout(() => console.log('2'), 0);
  
  Promise.resolve().then(() => {
    console.log('3');
    setTimeout(() => console.log('4'), 0);
  });
  
  await Promise.resolve();
  console.log('5');
  
  queueMicrotask(() => console.log('6'));
}

demo();
console.log('7');

const config = {
  port: 0,
  timeout: null,
  retries: '',
  cache: false,
  debug: undefined
};

const port = config.port ?? 3000;
const timeout = config.timeout ?? 5000;
const retries = config.retries ?? 3;
const cache = config.cache ?? true;
const debug = config.debug ?? false;

console.log([port, timeout, retries, cache, debug]);

const team = {
  captain: { name: 'Jack', age: 35 },
  players: ['Bob', 'Alice', 'Mike'],
  details: { founded: 2020, league: 'Premier' }
};

const { 
  captain: { name }, 
  players: [, second],
  details: { league: division = 'Amateur' } 
} = team;

console.log(`${name}-${second}-${division}`);