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React Native Interview Questions and Answers

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React Native Interview Questions and Answers

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Most Asked React Native Interview Questions and Answers

Q1. What is React Native?

Ans: React Native is a JavaScript framework for building natively rendered mobile applications for iOS and Android. It uses React along with native platform capabilities to create cross-platform apps.

Q2. What is the difference between React and React Native?

Ans:

  • React: A library for building UIs, typically for web apps.
  • React Native: A framework for building native mobile apps using React. React Native uses components like <View> and <Text> instead of <div> and <span>.

Q3. What are props in React Native?

Ans: Props (short for properties) are immutable parameters passed to a component to control its behavior or appearance.

Q4. How does React Native achieve cross-platform functionality?

Ans: React Native uses a bridge to communicate between JavaScript and native modules, allowing developers to write code once and run it on multiple platforms.

Q5. What are the advantages of using React Native?

Ans:

  • Faster development due to code reuse.
  • Cross-platform support.
  • Large community support and libraries.
  • Live reload for quicker debugging.

Q6. What is the purpose of StyleSheet.create() in React Native?

Ans: It optimizes styles by ensuring immutability and minimizing bridge transfers between JavaScript and native code.

Q7. What is Flexbox, and how is it used in React Native?

Ans: Flexbox is a layout model used in React Native for creating responsive designs. It provides properties like flexDirection, justifyContent, and alignItems.

Q8. Explain the role of the JavaScript thread in React Native.

Ans: The JavaScript thread handles business logic, component rendering, and communication with the native side via the bridge.

Q9. How do you implement animations in React Native?

Ans: React Native provides Animated and LayoutAnimation APIs for creating smooth, native-like animations.

Q10. What is the difference between React Native and hybrid apps?

Ans: React Native uses native components, providing better performance, while hybrid apps use WebView, which can be slower.

Q11. How does React Native handle performance optimization?

Ans: By minimizing bridge usage, leveraging useNativeDriver for animations, and using tools like Hermes for better runtime performance.

Q12. How does React Native manage state?

Ans: It uses local state (useState) and external libraries like Redux, MobX, or Context API for global state management.

Q13. Can you use native code in a React Native app?

Ans: Yes, native code written in Java/Swift/Objective-C can be integrated for tasks requiring platform-specific functionality.

Q14. What is the difference between a controlled and uncontrolled component?

Ans: Controlled components have their state managed by React, while uncontrolled components manage their own state using refs.

Q15. What debugging tools can be used with React Native?

Ans:

  • React Native Debugger
  • Flipper
  • Chrome DevTools

Q16. How do you optimize images in React Native?

Ans: By using libraries like react-native-fast-image or resizing images on the server side to reduce load time.

Q17. What are some popular navigation libraries in React Native?

Ans:

  • React Navigation
  • React Native Navigation

Q18. What is the role of Metro bundler?

Ans: Metro is a JavaScript bundler specifically designed for React Native apps. It optimizes the delivery of JS code to the app.

Q19. How do you implement localization in React Native?

Ans: Use libraries like react-native-i18n or react-intl to provide multi-language support.

Q20. What are common performance pitfalls in React Native apps?

Ans:

  • Overloading the bridge with data.
  • Inefficient re-renders.
  • Poor image handling.

Q21. How do you handle deep linking in React Native?

Ans: By using libraries like @react-navigation/native and configuring platform-specific files.

Q22. Explain how you’d set up push notifications in a React Native app.

Ans: Use services like Firebase Cloud Messaging and integrate with native modules for iOS and Android

Q23. How do you handle permissions in React Native?

Ans: Use libraries like react-native-permissions to manage user permissions.

Q24. What is the purpose of useNativeDriver in animations?

Ans: It allows animations to run directly on the native side, bypassing the bridge for better performance.

Q25. How do you implement offline support in React Native?

Ans: Use libraries like react-native-offline or cache data locally using AsyncStorage or SQLite.

Q26. How would you fetch data from an API and display it in a FlatList?

Ans:

import React, { useEffect, useState } from 'react';
import { FlatList, Text, View, StyleSheet } from
    'react-native';
const FetchDataList = () => {
    const [data, setData] = useState([]);
    const [loading, setLoading] = useState(true);
    useEffect(() => {
        fetch('https://jsonplaceholder.typicode.com/posts')
            .then((response) => response.json())
            .then((json) => {
                setData(json);
                setLoading(false);
            })
            .catch((error) => console.error(error));
    }, []);

    if (loading) {
        return (
            <View style= { styles.loading } >
            <Text>Loading...</Text>
                </View>
);
}

return (
    <FlatList data= { data }
keyExtractor = {(item) => item.id.toString()}
renderItem = {({ item }) => (
    <View style= { styles.item } >
    <Text style={ styles.title }> { item.title } </Text>
        < Text > { item.body } </Text>
        </View>
)}
/>
);
};

const styles = StyleSheet.create({
    loading: {
        flex: 1,
        justifyContent: 'center',
        alignItems: 'center',
    },
    item: {
        padding: 10,
        borderBottomWidth: 1,
        borderBottomColor: '#ccc',
    },
    title: {
        fontWeight: 'bold',
    },
});

export default FetchDataList;

Q27. How does Flexbox work in React Native?

Ans: Flexbox is a layout system in React Native for creating responsive designs. It allows you to define the direction (flexDirection), alignment (alignItems), and space distribution (justifyContent) of elements.

Code Example:

import React from 'react';
import { View, Text, StyleSheet } from 'react-native';

const FlexboxExample = () => {
  return (
    <View style={styles.container}>
      <View style={styles.box}>
        <Text>Box 1</Text>
      </View>
      <View style={styles.box}>
        <Text>Box 2</Text>
      </View>
      <View style={styles.box}>
        <Text>Box 3</Text>
      </View>
    </View>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'row', // Horizontal layout
    justifyContent: 'space-between', // Space between items
    alignItems: 'center', // Align items vertically
    padding: 20,
  },
  box: {
    width: 80,
    height: 80,
    backgroundColor: 'lightblue',
    justifyContent: 'center',
    alignItems: 'center',
    margin: 5,
  },
});

export default FlexboxExample;

Q28 What is the role of Hermes in React Native?

Ans: Hermes is a lightweight JavaScript engine designed to improve app startup time and performance.

Q29  How do you handle navigation in React Native?

Ans: React Navigation is a popular library for routing and navigation in React Native apps. It provides different types of navigators, such as stack, tab, and drawer navigators.

Code Example: Basic Stack Navigation

npm install @react-navigation/native @react-navigation/stack react-native-screens 
react-native-safe-area-context react-native-gesture-handler 
react-native-reanimated react-native-vector-icons

import React from 'react';

import { Button, View, Text } from 'react-native';

import { NavigationContainer } from '@react-navigation/native';

import { createStackNavigator } from '@react-navigation/stack';


const HomeScreen = ({ navigation }) => (
  <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
    <Text>Home Screen</Text>
    <Button title="Go to Details" onPress={() => navigation.navigate('Details')} />
  </View>
);

const DetailsScreen = () => (
  <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
    <Text>Details Screen</Text>
  </View>
);

const Stack = createStackNavigator();

const App = () => (

  <NavigationContainer>
    <Stack.Navigator initialRouteName="Home">
      <Stack.Screen name="Home" component={HomeScreen} />
      <Stack.Screen name="Details" component={DetailsScreen} />
    </Stack.Navigator>
  </NavigationContainer>
);

export default App;

Q30. Handling Image Loading with FastImage ?

Ans: FastImage is a React Native library that provides fast image rendering and caching. It’s optimized for performance compared to the standard Image component and reduces loading times for images, especially large ones.

Code Example:

npm install react-native-fast-image


import React from 'react';
import FastImage from 'react-native-fast-image';
import { View, StyleSheet } from 'react-native';

const FastImageExample = () => {
  return (
    <View style={styles.container}>
      <FastImage style={styles.image}
        source={{
          uri: 'https://example.com/image.jpg',
          priority: FastImage.priority.high,
        }}
        resizeMode={FastImage.resizeMode.contain}
      />
    </View>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
  },
  image: {
    width: 200,
    height: 200,
  },
});

export default FastImageExample;

 

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