Patrones practicos

Fetch con async/await

function Users() {
  const [users, setUsers] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    // No puedes hacer useEffect async directamente
    // Crea una funcion async dentro
    const fetchUsers = async () => {
      try {
        setLoading(true);
        const res = await fetch('/api/users');

        if (!res.ok) throw new Error('Error al cargar');

        const data = await res.json();
        setUsers(data);
      } catch (err) {
        setError(err.message);
      } finally {
        setLoading(false);
      }
    };

    fetchUsers();
  }, []);

  if (loading) return <p>Cargando...</p>;
  if (error) return <p>Error: {error}</p>;

  return (
    <ul>
      {users.map(u => <li key={u.id}>{u.name}</li>)}
    </ul>
  );
}

Debounce de busqueda

function Search() {
  const [query, setQuery] = useState('');
  const [results, setResults] = useState([]);

  useEffect(() => {
    if (!query) {
      setResults([]);
      return;
    }

    // Espera 300ms antes de buscar
    const timer = setTimeout(() => {
      fetch(`/api/search?q=${query}`)
        .then(res => res.json())
        .then(setResults);
    }, 300);

    return () => clearTimeout(timer);
  }, [query]);

  return (
    <div>
      <input
        value={query}
        onChange={(e) => setQuery(e.target.value)}
        placeholder="Buscar..."
      />
      <ul>
        {results.map(r => <li key={r.id}>{r.title}</li>)}
      </ul>
    </div>
  );
}

Local Storage

function useLocalStorage(key, initialValue) {
  const [value, setValue] = useState(() => {
    const saved = localStorage.getItem(key);
    return saved ? JSON.parse(saved) : initialValue;
  });

  useEffect(() => {
    localStorage.setItem(key, JSON.stringify(value));
  }, [key, value]);

  return [value, setValue];
}

// Uso
function App() {
  const [theme, setTheme] = useLocalStorage('theme', 'light');

  return (
    <button onClick={() => setTheme(t => t === 'light' ? 'dark' : 'light')}>
      Tema: {theme}
    </button>
  );
}

Evitar efectos innecesarios

// MAL - efecto innecesario
function Form() {
  const [firstName, setFirstName] = useState('');
  const [lastName, setLastName] = useState('');
  const [fullName, setFullName] = useState('');

  useEffect(() => {
    setFullName(firstName + ' ' + lastName);
  }, [firstName, lastName]);
}

// BIEN - calcula durante el render
function Form() {
  const [firstName, setFirstName] = useState('');
  const [lastName, setLastName] = useState('');

  // Derivado, no necesita estado
  const fullName = firstName + ' ' + lastName;
}