What is React Native and how does it differ from React?

React is a JavaScript library for building web UIs. React Native uses the same component model and JSX syntax but renders to native mobile components instead of HTML. A View in React Native becomes a UIView on iOS and android.view.View on Android. You write JavaScript but the user sees a native app.

What is the difference between a functional component and a class component?

Functional components are plain functions that accept props and return JSX. Class components extend React.Component and use lifecycle methods. Since React 16.8, functional components with hooks are the standard.

Explain the useState and useEffect hooks.

useState declares a state variable and returns the current value and a setter function. useEffect runs side effects after render. Pass it a function and a dependency array. Empty array means it runs once on mount. Return a cleanup function for subscriptions or timers.

How does the Virtual DOM work in React Native?

React Native uses a virtual representation of the native UI tree. When state changes, React creates a new virtual tree, diffs it against the previous one, and sends only the minimal set of changes to the native side through the bridge.

What is the difference between ScrollView and FlatList?

ScrollView renders all its children at once, which eats memory on long lists. FlatList virtualizes the list, only rendering items currently visible on screen. Always use FlatList for lists longer than a couple dozen items.

React Native Interview Questions: Junior to Senior