Interview question

What are keys and why are they important in rendering lists? Keys क्या हैं और lists render करते समय क्यों महत्वपूर्ण हैं?

Answer

// GOOD - using unique ID
function TodoList({ todos }) {
  return (
    <ul>
      {todos.map(todo => (
        <li key={todo.id}>{todo.text}</li>
      ))}
    </ul>
  );
}

// BAD - using index (can cause bugs)
function TodoList({ todos }) {
  return (
    <ul>
      {todos.map((todo, index) => (
        <li key={index}>{todo.text}</li>
      ))}
    </ul>
  );
}

// Why keys matter:
// 1. Help React identify changed items
// 2. Preserve component state
// 3. Maintain form input values
// 4. Avoid UI bugs when reordering

Keys का महत्व:
1. React को identify करने में help
2. State preserve करता है
3. Form values maintain करता है
4. Always use unique IDs, not index

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