Most common React.js interview questions

In this article, I will try to include some of the most common React.js interview questions with their answers.

1. What is React.js?
- React.js is an open-source JavaScript library used for building user interfaces and web applications.

2. What is JSX in React.js?
- JSX is a syntax extension used in React.js that allows developers to write HTML-like code within their JavaScript code.

3. What is the difference between a functional component and a class component in React.js?
- Functional components are simpler and lighter weight than class components, as they are simply JavaScript functions that return React elements.
- Class components are more powerful and can have state and lifecycle methods.

4. What is the virtual DOM in React.js?
- The virtual DOM is a lightweight copy of the actual DOM used in React.js to improve performance by minimizing the number of updates needed to the actual DOM.

5. What is the purpose of state in React.js?
- State is used in React.js to manage the data and state of a component, allowing it to update and re-render based on changes to its data.

6. What is a prop in React.js?
- A prop is a read-only property passed down from a parent component to a child component, allowing the child component to receive data and configuration from the parent.

7. What is the purpose of the componentDidMount() lifecycle method in React.js?
- The componentDidMount() method is used in React.js to perform actions or fetch data after a component has mounted or rendered on the page.

8. What is the purpose of the shouldComponentUpdate() lifecycle method in React.js?
- The shouldComponentUpdate() method is used in React.js to optimize performance by determining whether a component should update and re-render based on changes to its data.

9. What is the purpose of the setState() method in React.js?
- The setState() method is used in React.js to update the state of a component, triggering a re-render of the component and any child components that depend on its state.

10. What is the purpose of the key prop in React.js?
- The key prop is used in React.js to give each child component in a list a unique identifier, allowing React to efficiently update and re-render the list as needed.

That’s all, now you have good knowledge about the most common React.js questions being asked in interviews.

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