function processData({ a = 10, b = 20 } = { a: 30 }) {
  console.log(a, b);
}

processData({ a: 5, b: 10 });
processData();

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 regex = /^pear/gm;
const str = `dog
cat
bat`;
console.log(str.match(regex));

function* gen() {
  yield* ['x', 2, 3].map(x => x * 2);
}

const iterator = gen();
console.log(iterator.next().value);
console.log(iterator.next().value);
console.log(iterator.next().value);
console.log(iterator.next().value);

function test() {
  console.log(arguments.length);
}

test(1, 2, 3);
test.call(null, null, null, null);

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);

❓Что будет на выходе?

const range = Array.from({ length: 5 }, (_, index) =>
index + 1);
console.log(range);

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);

const map = new Map();
const key1 = {};
const key2 = key1;

map.set(key1, "Value for key1");
map.set(key2, "Value for key2");

console.log(map.get(key2));
console.log(map.get(key1));

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);

function foo() {
    var secondDigit = 1
    let firstDigit = secondDigit
    firstDigit++
    return firstDigit
}
 
foo()
console.log(typeof firstDigit)
console.log(typeof secondDigit)

var a=[1,3,6,9,12,24,36,72,15]
var b=a.filter(x=>x%2==0&&x%3==0&&x%4==0)
console.log(b)

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());

const arr = [3, 8, 12];
const even = (elem) => elem % 2 === 0;

console.log(arr.map(even));

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);

const a = [1,2,3];
const b = a.reverse();
const c = a.reverse();

console.log(a);
console.log(b);
console.log(c);

const obj = { x: 1, y: 2 };
let {x: a, y: b } = obj;
a = 2;
console.log(a, obj.y);

const company = {
  name: 'TechCorp',
  departments: {
    engineering: {
      head: { name: 'Alice', contact: null },
      staff: 50
    },
    marketing: null
  }
};

const engineeringContact = company.departments.engineering.head.contact;
const marketingHead = company.departments.marketing?.head?.name;
const financeStaff = company?.departments?.finance?.staff ?? 'Not available';

console.log(`${engineeringContact} - ${marketingHead} - ${financeStaff}`);

const obj = Object.freeze({
  a: [1, 2, 3],
  b: {
    c: 4
  }
});

obj.a.push(obj.b);
obj.b.c = 5;

console.log(obj.a);
console.log(obj.a.b);

function A() {}
function B() {}

A.prototype = B.prototype = {};

let a = new A();
let b = new B();

console.log( b instanceof A );