React Native Interview Questions & Answers for Beginners - Part 1

 Came up with the list of React Native interview question which i usually ask for candidates in Interviews.

• What is React Native?

                React Native is an open-source framework developed by Facebook for building mobile applications using JavaScript and React. It allows developers to build native mobile apps for iOS and Android platforms with a single JavaScript codebase. 

                React Native works by invoking native rendering APIs in Objective-C (for iOS) or Java (for Android). Thus, your application will render using real mobile UI components, not webviews, and will look and feel like any other mobile application. React Native also exposes JavaScript interfaces for platform APIs, so your React Native apps can access platform features like the phone camera, or the user's location.

• How does React Native differ from React?

                React is a JavaScript library for building user interfaces, primarily for web applications. It introduces the concept of reusable components with a virtual DOM to optimize rendering and provide a fast and responsive user experience.

                React Native, on the other hand, is a framework that allows you to build mobile applications in JavaScript while still offering the performance of native applications. It's based on React, so it uses the same design and principles, but it targets mobile platforms instead of the browser.

                In React, for the web, you would use components like div, span, etc., which are HTML elements. In React Native, you use components like View, Text, and Image, which are native components, not HTML elements.

                React Native allows you to write some components in Swift, Objective-C, Java, or Kotlin if you need to optimize some aspects of your application for better performance, something you can't do with just React.

                So, while both React and React Native are used to build user interfaces with reusable components, React is used for web development, and React Native is used for mobile application development.

• What are some advantages of using React Native?

1. Code Reusability: React Native allows developers to use the same code for developing both iOS and Android applications. This can significantly reduce development time and cost.
2. Community Support: React Native has a large and active community of developers. This means that it's easy to find resources, tutorials, and third-party plugins.
3. Live and Hot Reloading: React Native supports both live and hot reloading, which can speed up development by automatically refreshing the app during development as soon as you save changes.
4. Performance: React Native performance is close to native because it uses native components for rendering.
5. Integration with JavaScript ecosystem: React Native allows you to leverage the vast JavaScript ecosystem, including libraries, tools, and more.
6. Expo Integration: Expo is a toolchain built around React Native to help you build native iOS and Android projects using JavaScript and React. It provides a set of tools that simplify the process of building, deploying, and quickly iterating on iOS, Android, and web apps from the same JavaScript/TypeScript codebase.
7. Familiarity for Web Developers: For developers already familiar with web development in React, transitioning to mobile app development with React Native can be smoother and faster.

• Can you explain the concept of the Virtual DOM?

                The Virtual DOM (VDOM) is a programming concept where an ideal, or "virtual", representation of a UI is kept in memory and synced with the "real" DOM by a library such as ReactDOM. This process is called reconciliation.

                In React, when a component's state changes, the entire UI is re-rendered in the Virtual DOM representation. Then, the difference between the previous Virtual DOM representation and the new one is calculated. Once these differences, or "diffs", are calculated, React updates the real DOM with only these differences. This is significantly more efficient than re-rendering the entire UI in the real DOM, which is what would happen without the Virtual DOM.

                This process allows for highly efficient updates and changes to the DOM, leading to smoother and faster performance of React applications. It's one of the reasons why React is so popular for building fast and responsive web applications.

• What is JSX and how is it used in React Native?

            JSX (JavaScript XML) is a syntax extension for JavaScript that is used to describe what the UI should look like. It is used in React and React Native to write the render methods of components. JSX produces React "elements" and has a syntax very similar to HTML.

            In React Native, you use JSX to define your components' UI. It's a mix of JavaScript and XML-like syntax inside the same script.

            Here's an example from your App.js file:

        export default function App() {

              return (

                <View style={styles.container} testID="app-container">

                  <Text>My First RN Expo App!</Text>

                  <StatusBar style="auto" />

                </View>

              );

        }

            In this example, <View>, <Text>, and <StatusBar> are all JSX elements. They look like HTML tags, but they are actually instances of React components.

            JSX is not required to use React or React Native, but it makes the code more readable and writeable, especially for developers coming from an HTML or XML background. It's also worth noting that JSX is compiled into regular JavaScript objects during the build process, so it doesn't have any performance impact.

• How do you handle local state in a React Native application?

            In a React Native application, state is handled in a similar way to how it's handled in a React application. State represents a part of the app that can change over time, and it can be handled in a few different ways:

            Local Component State: This is the state that is local to a component and can be managed using the useState hook in functional components or this.state and this.setState in class components. This is useful for state that is only relevant to a single component or closely related components.

        // Using useState hook in a functional component

        import React, { useState } from 'react';

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

        const MyComponent = () => {

              const [count, setCount] = useState(0);

              return (

                <>

                  <Text>You clicked {count} times</Text>

                  <Button onPress={() => setCount(count + 1)} title="Click me" />

                </>

              );

        };