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}`);

const handler = {
  get: (target, prop) => {
    if (prop in target) {
      return target[prop] * 2;
    }
    return 100;
  }
};

const nums = new Proxy({ a: 5, b: 10 }, handler);
console.log(nums.a, nums.b, nums.c);

async function fetchData() {
  const promise = new Promise(resolve => {
    setTimeout(() => resolve('first'), 2000);
  });
  
  console.log('start');
  const result = await promise;
  console.log(result);
  console.log('end');
}

fetchData();
const x = 'after';
console.log(x);

function* counter() {
  let count = 1;
  while (true) {
    const reset = yield count;
    count = reset ? 1 : count + 1;
  }
}

const gen = counter();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next(true).value);
console.log(gen.next().value);

const user = {
  profile: {
    name: "Alice",
    settings: null
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

const admin = {
  profile: {
    name: "Admin"
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

console.log(user.getPreferences());
console.log(admin.getPreferences());
console.log(user.profile.extra?.id?.toString());

function Animal(name) {
  this.name = name;
}

Animal.prototype.speak = function() {
  return `${this.name} makes a noise`;
};

function Dog(name) {
  Animal.call(this, name);
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.speak = function() {
  return `${this.name} barks`;
};

const animal = new Animal('Animal');
const dog = new Dog('Rex');

console.log(dog instanceof Animal);