React Snippets

import { useState, useEffect } from 'react';

function useLocalStorage<T>(key: string, initialValue: T) {
  const [value, setValue] = useState<T>(() => {
    if (typeof window === 'undefined') return initialValue;
    try {
      const stored = localStorage.getItem(key);
      return stored ? JSON.parse(stored) : initialValue;
    } catch {
      return initialValue;
    }
  });

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

  return [value, setValue] as const;
}

// Usage
const [theme, setTheme] = useLocalStorage('theme', 'dark');

import { useState, useEffect } from 'react';

function useDebounce<T>(value: T, delay = 300): T {
  const [debouncedValue, setDebouncedValue] = useState(value);

  useEffect(() => {
    const timer = setTimeout(() => setDebouncedValue(value), delay);
    return () => clearTimeout(timer);
  }, [value, delay]);

  return debouncedValue;
}

// Usage
function SearchComponent() {
  const [query, setQuery] = useState('');
  const debouncedQuery = useDebounce(query, 300);

  useEffect(() => {
    if (debouncedQuery) fetchResults(debouncedQuery);
  }, [debouncedQuery]);
}

import { useState, useEffect } from 'react';

function useMediaQuery(query: string): boolean {
  const [matches, setMatches] = useState(false);

  useEffect(() => {
    const media = window.matchMedia(query);
    setMatches(media.matches);

    const listener = (e: MediaQueryListEvent) =>
      setMatches(e.matches);
    media.addEventListener('change', listener);
    return () => media.removeEventListener('change', listener);
  }, [query]);

  return matches;
}

// Usage
const isMobile = useMediaQuery('(max-width: 768px)');
const prefersDark = useMediaQuery('(prefers-color-scheme: dark)');

// && short-circuit (careful with 0/NaN)
{items.length > 0 && <List items={items} />}

// Ternary
{isLoading ? <Spinner /> : <Content />}

// Early return (recommended for complex cases)
function UserProfile({ user }) {
  if (!user) return <NotFound />;
  if (user.banned) return <Banned />;
  return <Profile user={user} />;
}

// Object map (replaces switch)
const statusComponent = {
  loading: <Spinner />,
  error: <Error />,
  success: <Content />,
}[status];