React js interview question with answer

What is ReactJS and why is it popular?
ReactJS is a popular JavaScript library used for building user interfaces. It was developed by Facebook and has gained popularity due to its simplicity, flexibility, and performance. React uses a virtual DOM, which makes it fast and efficient, and its component-based architecture makes it easy to maintain and reuse code.

What are the differences between ReactJS and AngularJS?
ReactJS is a library, while AngularJS is a framework. React focuses mainly on the view layer of the application, while Angular provides a more complete set of features for building complex applications. React uses JSX syntax for defining components, while Angular uses HTML templates. React encourages a functional programming style, while Angular is more object-oriented.

What are React Hooks?
React Hooks are a new feature in React that allows developers to use state and other React features without writing a class component. Hooks allow developers to reuse stateful logic between components, making code more modular and easier to maintain.

What is Redux and how does it work with React?
Redux is a predictable state container for JavaScript applications. It helps manage the state of an application in a consistent and predictable way. Redux can be used with React to manage the state of a React application. React components can interact with the Redux store using the connect() function.

What is the significance of Virtual DOM in React?
The Virtual DOM is a lightweight representation of the actual DOM in memory. When a change occurs in the state of a React component, React creates a new Virtual DOM tree and compares it with the previous one. It then updates the actual DOM with only the changes that have occurred, minimizing the number of DOM manipulations and making the application faster.

How do you handle user input in React?
User input can be handled in React using form elements and event handlers. Form elements such as input, select, and textarea can be used to capture user input. Event handlers such as onChange, onSubmit, and onClick can be used to handle the user input and update the state of the application.

How do you optimize the performance of a React application?
There are several ways to optimize the performance of a React application, including:

Using the shouldComponentUpdate() method to prevent unnecessary re-renders
Using the React.memo() function to memoize components
Using the React.lazy() function to lazy-load components
Using the useCallback() hook to memoize event handlers
Using the useMemo() hook to memoize expensive computations
What are the differences between ReactJS and React Native?
ReactJS is used for building web applications, while React Native is used for building native mobile applications. React Native allows developers to write code once and deploy it on multiple platforms, while ReactJS is limited to the web. React Native uses native components, while ReactJS uses web components.

How do you handle errors in a React application?
Errors in a React application can be handled using error boundaries. An error boundary is a component that catches JavaScript errors anywhere in its child component tree and displays an error message instead of crashing the entire application. Error boundaries can be implemented using the componentDidCatch() method.

How do you test a React application?
React applications can be tested using various testing frameworks such as Jest, Enzyme, and React Testing Library. Unit tests can be written to test individual components, while integration tests can be written to test the interaction between components. End-to-end tests can be written to test the entire application flow. The testing can be automated using continuous integration and delivery tools such as Travis CI and Jenkins.


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