Custom Hooks

You are a React custom hooks expert. You help create reusable, well-typed custom hooks that encapsulate common patterns and logic.

Custom Hook Patterns

1. useLocalStorage - Persistent State

// hooks/​useLocalStorage.ts
import { useState, useEffect } from 'react';

export function useLocalStorage<T>(
  key: string,
  initialValue: T
): [T, (value: T | ((val: T) => T)) => void] {
  // Get initial value from localStorage or use provided initial value
  const [storedValue, setStoredValue] = useState<T>(() => {
    if (typeof window === 'undefined') {
      return initialValue;
    }

    try {
      const item = window.localStorage.getItem(key);
      return item ? JSON.parse(item) : initialValue;
    } catch (error) {
      console.error(`Error loading localStorage key "${key}":`, error);
      return initialValue;
    }
  });

  // Update localStorage when value changes
  const setValue = (value: T | ((val: T) => T)) => {
    try {
      const valueToStore = value instanceof Function ? value(storedValue) : value;
      setStoredValue(valueToStore);

      if (typeof window !== 'undefined') {
        window.localStorage.setItem(key, JSON.stringify(valueToStore));
      }
    } catch (error) {
      console.error(`Error setting localStorage key "${key}":`, error);
    }
  };

  return [storedValue, setValue];
}

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

  return (
    <button onClick={() => setTheme(theme === 'light' ? 'dark' : 'light')}>
      Current theme: {theme}
    </​button>
  );
}

2. useDebounce - Delay Value Updates

// hooks/​useDebounce.ts
import { useState, useEffect } from 'react';

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

  useEffect(() => {
    const handler = setTimeout(() => {
      setDebouncedValue(value);
    }, delay);

    return () => {
      clearTimeout(handler);
    };
  }, [value, delay]);

  return debouncedValue;
}

// Usage
function SearchBox() {
  const [searchTerm, setSearchTerm] = useState('');
  const debouncedSearchTerm = useDebounce(searchTerm, 500);

  useEffect(() => {
    if (debouncedSearchTerm) {
      // API call only happens 500ms after user stops typing
      api.search(debouncedSearchTerm);
    }
  }, [debouncedSearchTerm]);

  return <input value={searchTerm} onChange={(e) => setSearchTerm(e.target.value)} />;
}

3. useMediaQuery - Responsive Breakpoints

// hooks/​useMediaQuery.ts
import { useState, useEffect } from 'react';

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

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

    // Set initial value
    setMatches(media.matches);

    // Create event listener
    const listener = (e: MediaQueryListEvent) => setMatches(e.matches);

    // Add listener
    media.addEventListener('change', listener);

    // Cleanup
    return () => media.removeEventListener('change', listener);
  }, [query]);

  return matches;
}

// Usage
function ResponsiveComponent() {
  const isMobile = useMediaQuery('(max-width: 768px)');
  const isTablet = useMediaQuery('(min-width: 769px) and (max-width: 1024px)');
  const isDesktop = useMediaQuery('(min-width: 1025px)');

  return (
    <div>
      {isMobile && <MobileView />}
      {isTablet && <TabletView />}
      {isDesktop && <DesktopView />}
    </​div>
  );
}

4. useOnClickOutside - Detect Outside Clicks

// hooks/​useOnClickOutside.ts
import { useEffect, RefObject } from 'react';

export function useOnClickOutside<T extends HTMLElement>(
  ref: RefObject<T>,
  handler: (event: MouseEvent | TouchEvent) => void
): void {
  useEffect(() => {
    const listener = (event: MouseEvent | TouchEvent) => {
      // Do nothing if clicking ref's element or descendent elements
      if (!ref.current || ref.current.contains(event.target as Node)) {
        return;
      }

      handler(event);
    };

    document.addEventListener('mousedown', listener);
    document.addEventListener('touchstart', listener);

    return () => {
      document.removeEventListener('mousedown', listener);
      document.removeEventListener('touchstart', listener);
    };
  }, [ref, handler]);
}

// Usage
function Dropdown() {
  const [isOpen, setIsOpen] = useState(false);
  const dropdownRef = useRef<HTMLDivElement>(null);

  useOnClickOutside(dropdownRef, () => setIsOpen(false));

  return (
    <div ref={dropdownRef}>
      <button onClick={() => setIsOpen(!isOpen)}>Toggle</​button>
      {isOpen && <div>Dropdown content</​div>}
    </​div>
  );
}

5. useAsync - Async Operation State

// hooks/​useAsync.ts
import { useState, useEffect, useCallback } from 'react';

interface AsyncState<T> {
  data: T | null;
  error: Error | null;
  isLoading: boolean;
}

export function useAsync<T>(
  asyncFunction: () => Promise<T>,
  immediate = true
): AsyncState<T> & { execute: () => Promise<void> } {
  const [state, setState] = useState<AsyncState<T>>({
    data: null,
    error: null,
    isLoading: immediate,
  });

  const execute = useCallback(async () => {
    setState({ data: null, error: null, isLoading: true });

    try {
      const data = await asyncFunction();
      setState({ data, error: null, isLoading: false });
    } catch (error) {
      setState({ data: null, error: error as Error, isLoading: false });
    }
  }, [asyncFunction]);

  useEffect(() => {
    if (immediate) {
      execute();
    }
  }, [execute, immediate]);

  return { ...state, execute };
}

// Usage
function UserProfile({ userId }: { userId: string }) {
  const { data: user, isLoading, error } = useAsync(
    () => api.getUser(userId),
    true
  );

  if (isLoading) return <div>Loading...</​div>;
  if (error) return <div>Error: {error.message}</​div>;
  if (!user) return null;

  return <div>{user.name}</​div>;
}

6. usePrevious - Track Previous Value

// hooks/​usePrevious.ts
import { useRef, useEffect } from 'react';

export function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T>();

  useEffect(() => {
    ref.current = value;
  }, [value]);

  return ref.current;
}

// Usage
function Counter() {
  const [count, setCount] = useState(0);
  const prevCount = usePrevious(count);

  return (
    <div>
      <p>Current: {count}</​p>
      <p>Previous: {prevCount}</​p>
      <button onClick={() => setCount(count + 1)}>Increment</​button>
    </​div>
  );
}

7. useToggle - Boolean State Toggle

// hooks/​useToggle.ts
import { useState, useCallback } from 'react';

export function useToggle(
  initialValue = false
): [boolean, () => void, (value: boolean) => void] {
  const [value, setValue] = useState(initialValue);

  const toggle = useCallback(() => {
    setValue((v) => !v);
  }, []);

  return [value, toggle, setValue];
}

// Usage
function Modal() {
  const [isOpen, toggleOpen, setIsOpen] = useToggle(false);

  return (
    <>
      <button onClick={toggleOpen}>Toggle Modal</​button>
      {isOpen && (
        <div>
          <p>Modal Content</​p>
          <button onClick={() => setIsOpen(false)}>Close</​button>
        </​div>
      )}
    </>
  );
}

8. useWindowSize - Track Window Dimensions

// hooks/​useWindowSize.ts
import { useState, useEffect } from 'react';

interface WindowSize {
  width: number;
  height: number;
}

export function useWindowSize(): WindowSize {
  const [windowSize, setWindowSize] = useState<WindowSize>({
    width: window.innerWidth,
    height: window.innerHeight,
  });

  useEffect(() => {
    const handleResize = () => {
      setWindowSize({
        width: window.innerWidth,
        height: window.innerHeight,
      });
    };

    window.addEventListener('resize', handleResize);
    return () => window.removeEventListener('resize', handleResize);
  }, []);

  return windowSize;
}

// Usage
function ResponsiveComponent() {
  const { width, height } = useWindowSize();

  return (
    <div>
      Window size: {width} x {height}
    </​div>
  );
}

Best Practices for Custom Hooks

1. Naming: Always start with "use" (React requirement)
2. Return Values:
   • Single value: Return directly
   • Multiple related values: Return as object
   • Pair of values (state/​setter): Return as tuple
3. TypeScript: Always add proper type definitions
4. Cleanup: Return cleanup functions from useEffect
5. Dependencies: Carefully manage dependency arrays
6. Memoization: Use useCallback for returned functions
7. Documentation: Add JSDoc comments for complex hooks

When to Create Custom Hooks

Create custom hooks when:

• Logic is reused across multiple components
• Complex state management logic needs encapsulation
• Side effects need to be abstracted
• Component logic becomes too complex
• You find yourself copying code between components

This skill helps you create reusable, well-designed custom hooks following React best practices.