Don’t Skip | Top 5 ReactJS Interview Topics and Detailed Solutions

Preparing for a ReactJS interview can be daunting, especially with the breadth of topics covered. To help you focus your study efforts, here are the top five ReactJS interview topics along with detailed explanations and solutions.

• Virtual DOM

Explanation: The Virtual DOM is a lightweight representation of the actual DOM. React uses it to optimize rendering performance by minimizing direct interactions with the real DOM.

Solution:

• When a component’s state changes, React creates a new Virtual DOM tree.
• It then compares this new tree with the previous one using a process called “reconciliation.”
• Only the differences (or “diffs”) are updated in the real DOM, which enhances performance.

  Example Question: “Explain how React updates the DOM using the Virtual DOM.”

• Components and Props

Explanation: Components are the building blocks of any React application. They can be functional or class-based and can accept inputs called props.

Solution:

• Functional Components: These are JavaScript functions that return JSX.
• Class Components: These extend `React.Component` and use `this.props` to access props.

Example Question: “What are props in React, and how do you pass data between components?”

• State Management

Explanation: State is an object that determines how that component renders and behaves. It is mutable and can change over time, typically in response to user actions.

Solution:

• Use “useState” hook in functional components to manage state:

•  In class components, use `this.state` and `this.setState()`:

Example Question: “How do you manage state in a React application?”

• Lifecycle Methods

Explanation: Lifecycle methods allow you to run code at specific points in a component’s life cycle (e.g., when it mounts, updates, or unmounts).

Solution:

•  Common lifecycle methods in class components include:

• ‘componentDidMount()’: Invoked immediately after a component is mounted.
• ‘componentDidUpdate(prevProps, prevState)’: Invoked immediately after updating occurs.
•  ‘componentWillUnmount()’: Invoked immediately before a component is unmounted.

• For functional components, use the useEffect hook to replicate lifecycle behavior:

Example Question: “What are the different lifecycle methods in React?”

• React Hooks

Explanation: Hooks are functions that let you use state and other React features without writing a class. They were introduced in React 16.8.

Solution:

• Common hooks include:

•  ‘useState’: For managing state in functional components.
•  ‘useEffect’: For performing side effects like data fetching or subscriptions.
• ‘useContext’: For accessing context values without prop drilling.

Example Question: “What are hooks in React, and how do they differ from class components?”

Conclusion

Focusing on these five key topics Virtual DOM, Components and Props, State Management, Lifecycle Methods, and React Hooks will provide you with a solid foundation for your upcoming ReactJS interview. Understanding these concepts not only prepares you for technical questions but also demonstrates your proficiency in building efficient and scalable applications with React.