What is the purpose of the key prop in React lists?

Keys help React identify which items have changed, been added, or removed.

<ul>
  {users.map((user) => (
    <li key={user.id}>{user.name}</li>
  ))}
</ul>

If keys are missing or not unique, React’s diffing may behave unpredictably.

✅ Always use stable, unique keys (like IDs) — not array indexes.