30 Most Common React Native Interview Questions for 2023 - IQCode

React Native: A Powerful JavaScript-Based Mobile Application Framework for iOS and Android

React Native is a popular mobile application framework that allows developers to use React to create exceptional mobile applications for both iOS and Android platforms. One of the significant benefits of using React Native is that developers can write code once and use it across both platforms. The applications created with React Native are highly end-user-friendly, providing a native look and feel to both the end-users and the developers. If you are interested in learning more about React Native, visit their official website at https://reactnative.dev/.

React Native Basic Interview Questions

Q: How is React Native different from ReactJS?</br>
A: React Native is a mobile application framework that allows developers to create native mobile applications for iOS and Android platforms using the React library. On the other hand, ReactJS is a JavaScript library that is used for building user interfaces and is used primarily for web development applications. </br>

Understanding Flexbox and its Most Commonly Used Properties

Flexbox is a layout module in CSS that helps developers efficiently arrange and align elements within a container. Its most commonly used properties include:

1. display: flex; - This property defines a flex container, enabling flexbox properties to be applied to its children.

2. flex-direction: row/column - This property specifies the direction in which flex items are arranged within the flex container - either horizontally in a row or vertically in a column.

3. justify-content: center/flex-start/flex-end/space-between/space-around - This property defines how flex items are positioned along the main axis of the flex container.

4. align-items: center/flex-start/flex-end/stretch/baseline - This property specifies how flex items are positioned along the cross axis of the flex container.

5. flex-wrap: wrap/nowrap - This property determines whether flex items should wrap onto a new line when the container overflows.

6. flex: none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]

i. flex-grow - This property specifies how much a flex item will grow relative to its siblings when there is extra space. ii. flex-shrink - This property determines how much a flex item will shrink relative to its siblings when there isn't enough space. iii. flex-basis - This property sets the initial size of a flex item before any available extra space is distributed.

By mastering Flexbox and its various properties, developers can easily and effectively create flexible and responsive layouts.

Advantages of Using React Native

React Native is a popular JavaScript framework for building native mobile applications. Here are some advantages of using React Native:

1. Cross-Platform Compatibility: React Native enables developers to build applications for both Android and iOS platforms with a single codebase. This helps save time and resources.

2. Faster Development: React Native's modular architecture and pre-built components allow for faster app development and easier maintenance.

3. Reusable Code: React Native's code can be shared across multiple platforms, which significantly reduces development time and cost.

4. Improved Performance: Since React Native apps are built with native components, they have better performance than hybrid apps.

5. Hot Reloading: React Native’s hot reloading feature allows developers to see the changes made in real-time, which speeds up the testing and debugging process.

Overall, React Native is a popular choice among developers because it allows for faster development, improved performance, and easier maintenance of mobile applications.

Threads in React Native

In general, a thread is a unit of execution within a process. It allows a program to perform multiple tasks concurrently. In React Native, there are three types of threads:

1. Main Thread - This is the thread where the UI rendering takes place. All React Native UI updates and state changes occur on this thread. It should not be blocked, as that would cause the application to freeze.

2. JavaScript Thread - This is where the JavaScript code of the application is executed. All JavaScript code runs on this thread, including event handling and network requests. This thread can be blocked by long-running JavaScript code, which can cause the application to become unresponsive.

3. Native Modules Thread - This thread is used to execute native code that is called from the JavaScript thread. It is a separate thread to prevent blocking the JavaScript thread.

It's important to understand these thread types and how they interact with each other to write efficient and responsive React Native applications.

Default Props in React Native

Yes, default props are available in React Native. Default props are used to provide default values for props in case they are not passed by the parent component.

Here's an example of how to use default props in a functional component:

  import React from 'react';
  import { Text } from 'react-native';

  const MyComponent = ({ name, age }) => {
    return (
      <Text>
        My name is {name} and I am {age} year(s) old.
      </Text>
    );
  };

  MyComponent.defaultProps = {
    name: 'John Doe',
    age: 30,
  };

  export default MyComponent;

In the above example, if the parent component uses without passing any props, default props of name: 'John Doe' and age: 30 will be used instead.

Default props can also be used in class components by defining a static defaultProps object:

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

  class MyComponent extends Component {
    static defaultProps = {
      name: 'John Doe',
      age: 30,
    };

    render() {
      const { name, age } = this.props;
      return (
        <Text>
          My name is {name} and I am {age} year(s) old.
        </Text>
      );
    }
  }

  export default MyComponent;

By using default props, you can avoid having to handle cases where props are not provided in your component's logic.

Handling User Input in React Native

In React Native, you can handle user input by using various UI components such as TextInput, Button, TouchableHighlight, TouchableOpacity, and TouchableWithoutFeedback. These components provide different types of interactions that can be used to capture user input and trigger specific actions.

To capture user input from TextInput, you can use the onChangeText prop to define a function that updates the component's state. For example:

import React, { useState } from 'react';
import { TextInput } from 'react-native';

const MyTextInput = () => {
  const [text, setText] = useState('');

  const handleInputChange = (inputValue) => {
    setText(inputValue);
  }

  return (
    <TextInput
      placeholder="Type here"
      onChangeText={handleInputChange}
      value={text}
     />
  );
};

In the above example, we define a TextInput component that captures user input and updates the value of the text state using the handleInputChange function. The text state is then used to display the user's input within the TextInput component.

Button, TouchableHighlight, TouchableOpacity, and TouchableWithoutFeedback can be used to capture user input and trigger specific actions. For example:

import React from 'react';
import { View, Button, TouchableHighlight, TouchableOpacity, TouchableWithoutFeedback } from 'react-native';

const MyButtons = () => {
  const handleButtonClick = () => {
    // Do something when button is clicked
  }

  const handleHighlightPress = () => {
    // Do something when touchable highlight is pressed
  }

  const handleOpacityPress = () => {
    // Do something when touchable opacity is pressed
  }

  const handleFeedbackPress = () => {
    // Do something when touchable without feedback is pressed
  }

  return (
    <View>
      <Button
        onPress={handleButtonClick}
        title="Click me"
      />
      <TouchableHighlight onPress={handleHighlightPress}>
        <View>
          <Text>Highlight me</Text>
        </View>
      </TouchableHighlight>
      <TouchableOpacity onPress={handleOpacityPress}>
        <View>
          <Text>Opacity me</Text>
        </View>
      </TouchableOpacity>
      <TouchableWithoutFeedback onPress={handleFeedbackPress}>
        <View>
          <Text>No feedback needed</Text>
        </View>
      </TouchableWithoutFeedback>
    </View>
  );
};

In the above example, we define four different components that capture different types of user input and trigger specific actions when pressed or clicked. These actions can be defined using functions that perform specific operations or update state.

Understanding the Role of State in React Native

In React Native, state is a built-in feature that allows developers to manage and store data within a component. It is a JavaScript object that contains data that can be updated over time, typically as a response to user actions or changes in the application's state.

State is commonly used to update a component’s UI based on user interactions, such as showing a notification after a user completes an action or displaying the current value of an input field. It can also be used to manage application logic, such as tracking the application’s current mode or determining which data to display based on user preferences.

In order to use state in a React Native component, you need to initialize it in the constructor method as a JavaScript object. You can then update the state using the setState() method, which will trigger a re-render of the component and update the UI as needed.

Overall, using state in React Native can help simplify your code and make it easier to manage complex data structures and application logic. Just be sure to use it wisely and avoid overcomplicating the state management process.

Understanding Redux in React Native and its Key Components

Redux is a state management library that facilitates the development of complex applications by making it easy to manage the data flow. It is primarily used in React Native apps to enable efficient state management and thus, streamline app development.

Some of the essential components used in Redux for React Native apps include:

1. Store: This holds the app state and provides a way to access it.

2. Reducer: This is a pure function that “reduces” the existing state and updates it with the new state.

3. Actions: These are plain JavaScript objects that describe the changes in the app state.

4. Dispatch: This is a method that dispatches actions to the reducers to update the app state.

5. Middleware: This is an optional feature that allows developers to extend the behavior of Redux.

By using Redux in your React Native app, you can easily manage state changes and make the development process more efficient.

Timers in React Native Application

In React Native, timers are used to execute a block of code after a specific time interval. There are three types of timers that can be used in a React Native application:

1. setTimeout - It executes the block of code once after a specified time interval in milliseconds. 2. setInterval - It executes the block of code repeatedly after a specified time interval in milliseconds until it is stopped. 3. requestAnimationFrame - It executes the block of code before the next repaint in the browser and is used for animations.

To use timers in a React Native application, we can use the global functions setTimeout, setInterval, and requestAnimationFrame provided by the JavaScript environment. We can also use the TimerMixin provided by the React package to create timers in a React component.

It's important to handle timers correctly in a React Native application as it can cause memory leaks if not implemented properly. Therefore, it's recommended to clear the timers using clearTimeout or clearInterval when they are no longer needed or when the component is unmounted.

Debugging React Native Applications: Tools and Techniques

Debugging is an essential process for ensuring the smooth functioning of any software. In the case of React Native applications, debugging becomes all the more important due to the unique development environment. Below are some tools and techniques that can be used for debugging React Native applications:

<!-- Code here -->

Some of the commonly used tools for debugging React Native applications include:

- React Developer Tools: A Chrome extension that allows developers to debug their React Native application by providing a visual representation of the component hierarchy, as well as the current state and props of each component.
- React Native Debugger: A standalone app that enables developers to debug their applications by providing a console to execute code, inspect the application state, and more.
- Chrome DevTools: A built-in debugging tool in Chrome that offers a range of features to debug React Native applications, including real-time reloading, live editing, network analysis, and more.
- Redux DevTools: For debugging Redux state management, including time-travel debugging, state inspection, and more.

In addition to these tools, there are also techniques that can be used while debugging React Native applications. One of the most common techniques is to use React Native's built-in debugging tools, such as the console.log function. Another technique is to use the React Native Debugger, which provides a range of debugging features and can be used to launch the application with debugging enabled.

Debugging React Native applications can be a challenging task, but with the right tools and techniques, it can help identify and fix errors, ensuring the application is running smoothly.

Understanding Props Drilling and How to Avoid it

Props drilling refers to the process of passing data through multiple levels of components in a React application. This can be a problem as it can make the code more complex and reduce its readability.

To avoid props drilling, we can use React's Context API which allows us to pass data to components without having to explicitly pass the data down through each level. We can create a context object using the createContext() method and use the Provider component to pass the data down to the child components.

Another way to avoid props drilling is by using higher-order components (HOC) which are functions that take a component and return a new component. With HOCs, we can wrap components with additional functionality without modifying its code.

By implementing these techniques, we can make our React code more efficient, maintainable and readable.

Networking in React Native: Making AJAX Network Calls

Networking is a crucial aspect of mobile development and React Native provides tools to enable making AJAX network calls. The XMLHttpRequest (XHR) API, compatible with modern web browsers, can be used to make network requests in React Native.

To make a network request, we need to import the ‘XMLHttpRequest’ module, create a new instance of it, and configure it with desired headers and options. We then use the ‘open()’ method to create a new HTTP request and specify the method, URL, and asynchronous mode. We then set the request header by calling ‘setRequestHeader()’ method and use the ‘send()’ method to send the request.

Once the request is sent, we need to handle the response. This can be done using the ‘onreadystatechange’ event listener that listens for state changes in the request. We can then check the status and response and handle it accordingly.

React Native also provides the ‘fetch()’ API that can be used to make network requests. It is a modern version of XHR with a simpler syntax and better error handling. We can use the ‘fetch()’ method to make a network request and handle the response using Promises.

Overall, networking in React Native is similar to web development, but with tools specific to mobile development. Understanding how to make network requests is a critical skill for mobile developers.

Key Points for Integrating React Native in an Existing Android Mobile Application:

When integrating React Native in an existing Android mobile application, here are the key points to consider:

1. Install Node.js and React Native
2. Create a new React Native project in the existing Android app
3. Configure the React Native project
4. Integrate native modules into the React Native project
5. Use React Native components in the existing Android app
6. Check compatibility with Android APIs and versions
7. Debug and test the React Native integration
8. Optimize the React Native integration for performance and stability

React Native Intermediate Interview Question:

Question 14: Can you describe the process of how React Native code is processed to display the final output on a mobile screen?

// The React Native code processing to display the final output on a mobile screen involves the following steps:
// 1. Once the developer writes React Native code and saves it in a file with .js extension, the Metro Bundler processes the code.
// 2. The Metro Bundler, which is the default JavaScript bundler for React Native, is responsible for taking all the JS code and organizing it into modules, processing dependencies and generating a single bundle file.
// 3. The generated bundle file is then sent to the JavaScriptBridge on the mobile device.
// 4. The JavaScriptBridge is responsible for executing the code and communicating with the native modules through the Native Modules Interface.
// 5. The Native Modules Interface allows communication between JavaScript and native code where there is a need to use native functionality, such as camera, accelerometer, or device storage.
// 6. The native code then processes the request and returns the data or result to the JavaScript side.
// 7. Once the data is received, the JavaScriptBridge creates a view hierarchy and sends instructions to the native module to render the views.
// 8. Finally, the view hierarchy is rendered on the mobile screen.

Bridge in React Native: Usage and Significance for Android and iOS

In React Native, a "bridge" is a communication layer between the JavaScript code and native platform-specific code, which enables a React Native application to run on both Android and iOS platforms.

The bridge allows for efficient communication over a network domain, improving the overall performance of the application, as well as acting as a mediator between the two platforms. For instance, if there is a function that needs to be executed on the native side, the bridge ensures that the correct functionality is called on the correct platform without any discrepancies.

On the Android platform, the bridge uses the Java Native Interface (JNI) to leverage the native code. JNI defines a standard interface that native implementations must adhere to, helping React Native to bypass unexpected errors or crashes during the app development.

On the iOS platform, the bridge makes use of Apple's Objective-C runtime to bind function calls between the React Native JavaScript code and the Objective-C code. It relies on a dynamic system of method resolution, which helps in binding methods during compile-time.

In summary, the Bridge in React Native is a fundamental part of the framework that provides an efficient way of communicating between the native and JavaScript code. Its usage and significance for both Android and iOS platforms enable developers to create a seamless user experience while leveraging their existing knowledge of JavaScript and native programming paradigms.

Core Components in React Native and their analogies with Web Components

React Native and Web development have similar concepts of components. Here are some of the core components in React Native and their analogies with web development:

- View: Similar to the `

#ifdef TARGET_IOS
    // iOS-specific code here
#endif

#ifdef TARGET_ANDROID
    // Android-specific code here
#endif

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

const CustomButton = ({ onPress, title }) => (
  <TouchableOpacity onPress={onPress}>
    <Text>{title}</Text>
  </TouchableOpacity>
);

export default CustomButton;

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

const data = [
  { id: 1, text: 'Item 1' },
  { id: 2, text: 'Item 2' },
  { id: 3, text: 'Item 3' },
  { id: 4, text: 'Item 4' },
  { id: 5, text: 'Item 5' },
];

const App = () => {
  const [listData, setListData] = useState(data);

  const renderItem = ({ item }) => (
    <View style={{ padding: 10 }}>
      <Text>{item.text}</Text>
    </View>
  );

  return (
    <FlatList
      data={listData}
      renderItem={renderItem}
      keyExtractor={(item) => item.id.toString()}
    />
  );
};

export default App;

<Text style={{ color: 'red', fontSize: 18 }}>Hello, World!</Text>

const styles = StyleSheet.create({
  text: {
    color: 'red',
    fontSize: 18
  },
  button: {
    backgroundColor: 'blue',
    paddingVertical: 10,
    paddingHorizontal: 20,
    borderRadius: 5
  }
});

<Text style={styles.text}>Hello, World!</Text>
<TouchableOpacity style={styles.button}>
  <Text style={{ color: 'white' }}>Click Me!</Text>
</TouchableOpacity>

const styles = StyleSheet.create({
  text: {
    fontSize: 18,
    ...Platform.select({
      ios: {
        color: 'blue',
      },
      android: {
        color: 'green',
      },
    }),
  }
})

<Text style={styles.text}>Hello, World!</Text>

1. Identify the areas of the application that need optimization.
<br>
2. Use caching to reduce the load on the server.
<br>
3. Minimize the use of external libraries and plugins.
<br>
4. Optimize images and other media files to reduce their file size.
<br>
5. Improve database performance by optimizing queries and minimizing requests.
<br>
6. Implement lazy loading for images and other media files.
<br>
7. Use Gzip compression to reduce the size of responses from the server.
<br>
8. Minimize the use of redirects to reduce server requests.
<br>
9. Optimize the code by removing unnecessary code and using more efficient coding practices.
<br>
10. Perform regular testing and monitoring to identify areas for further optimization.

1. Use "NativeDriver" for Animations <br>
2. Use "useMemo" or "useCallback" hooks to Memoize Animations <br>
3. Use "shouldComponentUpdate" or "React.memo" to Optimize Rerenders <br>
4. Use "requestAnimationFrame" to Schedule Animations <br>
5. Use "InteractionManager" to Prioritize Animations<br>
6. Use "FlatList" or "SectionList" for Large Lists<br>
7. Use "Touchable" Components Instead of "PanResponder"<br>