const arr = [1, [2, 3], [4, [5]]];
console.log(arr.flat()); // [1, 2, 3, 4, [5]]

const arr = [1, [2, 3], [4, [5, [6]]]];
console.log(arr.flat(2)); // [1, 2, 3, 4, 5, [6]]

const arr = [1, [2, [3, [4, [5]]]]];
console.log(arr.flat(Infinity)); // [1, 2, 3, 4, 5]

string.padStart(targetLength, padString)

const num = '42';
console.log(num.padStart(5, '0')); // "00042"

const day = '7';
const month = '3';
console.log(day.padStart(2, '0')); // "07"
console.log(month.padStart(2, '0')); // "03"
// Получаем: "03.07"

interface Device {
  print(doc: string): void;
  scan(doc: string): void;
  fax(doc: string): void;
}

class SimplePrinter implements Device {
  print(doc: string): void {
    console.log(`Печатаю: ${doc}`);
  }
  scan(doc: string): void {
    throw new Error('Не поддерживает сканирование');
  }
  fax(doc: string): void {
    throw new Error('Не поддерживает факс');
  }
}

interface Printable {
  print(doc: string): void;
}
interface Scannable {
  scan(doc: string): void;
}
interface Faxable {
  fax(doc: string): void;
}

class SimplePrinter implements Printable {
  print(doc: string): void {
    console.log(`Печатаю: ${doc}`);
  }
}

const users = [
  { name: "Аня", age: 25, city: "Москва" },
  { name: "Иван", age: 30, city: "Москва" },
  { name: "Оля", age: 22, city: "Казань" },
  { name: "Петя", age: 30, city: "Казань" },
];

const byCity = Object.groupBy(users, user => user.city);
console.log(byCity);
// {
//   "Москва": [ { name: "Аня", age: 25 }, { name: "Иван", age: 30 } ],
//   "Казань": [ { name: "Оля", age: 22 }, { name: "Петя", age: 30 } ]
// }

const byAge = Map.groupBy(users, user => user.age);
console.log(byAge);
// Map(3) {
//   25 => [ { name: "Аня", age: 25 } ],
//   30 => [ { name: "Иван", age: 30 }, { name: "Петя", age: 30 } ],
//   22 => [ { name: "Оля", age: 22 } ]
// }

{condition && <div>Component</div>}

{condition || secondCondition && <div>Component</div>}

{condition || (secondCondition && <div>Component</div>)}

{(condition || secondCondition) && <div>Component</div>}

{condition || secondCondition ? <div>Component</div> : null}

const { promise, resolve, reject } = Promise.withResolvers();

const { promise, resolve, reject } = Promise.withResolvers();

const ws = new WebSocket('wss://example.com');
ws.onmessage = event => resolve(event.data);
ws.onerror = error => reject(error);

promise
.then(data => console.log('Получено:', data))
.catch(error => console.error('Ошибка:', error));

let resolve, reject;
const promise = new Promise((res, rej) => {
  resolve = res;
  reject = rej;
});

function App() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    console.log("Effect:", count);
  }, [count]);

  const handleClick = () => {
    setCount(count + 1);
    setCount(count + 1);
    setCount(count + 1);
  };

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={handleClick}>+3</button>
    </div>
  );
}

function App() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    console.log("Effect:", count);
  }, [count]);

  const handleClick = () => {
    setCount(prev => prev + 1);
    setCount(prev => prev + 1);
    setCount(prev => prev + 1);
  };

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={handleClick}>+3</button>
    </div>
  );
}

<style>
  .wrapper {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
  }

  .inner {
    display: contents;
  }

  p {
    background: lightblue;
    padding: 10px;
  }
</style>

<div class="wrapper">
  <div class="inner">
    <p>Привет</p>
    <p>Мир</p>
  </div>
</div>

class Database {
  save(data: string): void {
    console.log(`Сохранено в базе: ${data}`);
  }
}

class UserService {
  private db = new Database();

  saveUser(user: string): void {
    this.db.save(user);
  }
}

const service = new UserService();
service.saveUser("Alice"); // Сохранено в базе: Alice

interface Storage {
  save(data: string): void;
}

class Database implements Storage {
  save(data: string): void {
    console.log(`Сохранено в базе: ${data}`);
  }
}

class FileStorage implements Storage {
  save(data: string): void {
    console.log(`Сохранено в файл: ${data}`);
  }
}

class UserService {
  constructor(private storage: Storage) {}

  saveUser(user: string): void {
    this.storage.save(user);
  }
}

const dbService = new UserService(new Database());
dbService.saveUser("Alice"); // Сохранено в базе: Alice

const fileService = new UserService(new FileStorage());
fileService.saveUser("Bob"); // Сохранено в файл: Bob

const users = [
  { name: 'Алиса', age: 21 },
  { name: 'Макс', age: 25 },
  { name: 'Ваня', age: 21 },
];

groupBy(users, user => user.age);
// Результат:
// {
//   21: [{ name: 'Алиса', age: 21 }, { name: 'Ваня', age: 21 }],
//   25: [{ name: 'Макс', age: 25 }]
// }

function groupBy(array, fn) {
  return array.reduce((acc, item) => {
    const key = fn(item);
    (acc[key] ||= []).push(item);
    return acc;
  }, {});
}