static-components

// ❌ Component defined inside component
function Parent() {
  const ChildComponent = () => { // New component every render!
    const [count, setCount] = useState(0);
    return <button onClick={() => setCount(count + 1)}>{count}</button>;
  };

  return <ChildComponent />; // State resets every render
}

// ❌ Dynamic component creation
function Parent({type}) {
  const Component = type === 'button'
    ? () => <button>Click</button>
    : () => <div>Text</div>;

  return <Component />;
}

// ✅ Components at module level
const ButtonComponent = () => <button>Click</button>;
const TextComponent = () => <div>Text</div>;

function Parent({type}) {
  const Component = type === 'button'
    ? ButtonComponent  // Reference existing component
    : TextComponent;

  return <Component />;
}

// ❌ Wrong: Inner component to access parent state
function Parent() {
  const [theme, setTheme] = useState('light');

  function ThemedButton() { // Recreated every render!
    return (
      <button className={theme}>
        Click me
      </button>
    );
  }

  return <ThemedButton />;
}

// ✅ Better: Pass props to static component
function ThemedButton({theme}) {
  return (
    <button className={theme}>
      Click me
    </button>
  );
}

function Parent() {
  const [theme, setTheme] = useState('light');
  return <ThemedButton theme={theme} />;
}