React

Hooks and state

• Do not use useEffect for simple state updates or derived state.
• Prefer direct calculations, useMemo, or useCallback when appropriate.
• Keep effects for real side effects: subscriptions, network sync, DOM/browser APIs, timers, external systems.

Avoid unnecessary declarations

• Inline simple logic directly in JSX.
• Do not extract simple handlers, variables, components, or helpers just for naming.
• Declare functions only when logic is complex, reused, or improves readability.

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

  return <button => setCount(count + 1)}>Count: {count}</button>;
}

Use a named handler only when the body is non-trivial:

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

  function handleIncrement() {
    // complex logic here eg: analytics, validation, side effects, 50 lines of code, etc.
    setCount(count + 1);
  }

  return <button {count}</button>;
}

Keep pure utilities outside components

• Pure functions that do not depend on component scope must live outside the component. This avoids recreating them on every render and keeps components focused.

function Message() {
  const [text, setText] = useState("");

  return (
    <>
      <p>{formatDisplayText(text)}</p>
      <input value={text} => setText(e.target.value)} />
    </>
  );
}

function formatDisplayText(text: string) {
  return text.toUpperCase();
}

Tailwind classes

• Prefer direct inline Tailwind classes in JSX.
• Do not extract class strings into variables, functions, or helpers.
• For conditional classes, avoid template literals and ternaries; use cn, clsx, or classnames inline.

<input
  className={cn(
    "w-full rounded-lg border px-4 py-2 focus:outline-none focus:ring-4",
    hasWarning && "border-yellow-500 bg-yellow-50 focus:ring-yellow-200",
    hasError && "border-red-500 bg-red-50 focus:ring-red-200",
  )}
/>