JS
React 19 Hooks Mastery

The Rules of Hooks

In this opening chapter, we review the absolute foundation of React 19 state management. The rules of hooks dictate order and determinism in rendering.

Hooks must always be called at the top level of a component function. You cannot nest them inside loops, conditions, or nested functions. This ensures they are called in the exact same order on every render, allowing React to properly preserve state between renders.

Additionally, hooks can only be called from inside React function components or custom hooks, never from regular JavaScript functions.

SnippetTSX
class=class="ttk-str">"ttk-cmt">// ❌ BAD: Conditional hook
if (isLoggedIn) {
  const [user, setUser] = useState(null);
}

class=class="ttk-str">"ttk-cmt">// ✅ GOOD: Hook at top level
const [user, setUser] = useState(null);

if (!isLoggedIn) {
  return <LoginScreen />;
}

Lesson Insights

Hooks must execute in the exact same order every render cycle

Never use hooks inside loops, `if` statements, or nested functions

Only call hooks from React components or custom hooks

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