Are you preparing for a ReactJS interview? If yes, you’re in the right place! In this article, we will go over the most frequently asked ReactJS interview questions, providing clear, easy-to-understand answers that will help you succeed in your interview. By the end, you’ll feel confident and ready to tackle any React-related questions that come your way.

Q1: How Does React Work?

Answer:
React uses a virtual DOM (Document Object Model) to enhance performance. When the state of a component changes, React runs a diffing algorithm to identify changes in the virtual DOM. After identifying the changes, React performs reconciliation to update the actual DOM with the differences. This results in efficient updates, minimizing expensive DOM manipulations.

Q2: What Are React Hooks?

Answer:
React Hooks, introduced in React 16.8, allow you to use state and other React features without writing class components. They enable you to extract stateful logic from a component and reuse it across multiple components. Hooks are great for testing and sharing stateful logic, making your components simpler and more readable. Some of the most commonly used hooks include useState, useEffect, and useContext.

Q3: What is Context API in ReactJS?

Answer:
The Context API allows you to pass data through the component tree without manually passing props at every level. It’s especially useful for sharing global data such as user authentication status, theme settings, or preferred language. Context allows you to avoid prop drilling, making your code cleaner and easier to maintain.

Example:

const ThemeContext = React.createContext('light');

In this example, the ThemeContext is provided at the top of the component tree and accessed by any component inside that tree.

Q4: What Are the Major Features of ReactJS?

Answer:
ReactJS comes with several powerful features:

• Virtual DOM for improved performance.
• Supports server-side rendering for better SEO and faster load times.
• Unidirectional data flow, making state management predictable.
• Reusable components that help build UI efficiently.

Q5: What Are the Advantages of ReactJS?

Answer:
ReactJS has several advantages that make it a popular choice among developers:

• Increased performance through Virtual DOM.
• JSX syntax simplifies writing and understanding code.
• Supports both client-side and server-side rendering.
• Easy integration with other frameworks (Angular, BackboneJS).
• Simplifies testing and integrates well with tools like JEST for UI testing.

Q6: What Are Props in React?

Answer:
Props (short for properties) are the mechanism by which data is passed from a parent component to a child component in React. Props allow you to customize or configure child components when they are created. These are read-only and help in triggering state changes in child components.

Example:

<Element reactProp="1" />

Here, reactProp is passed down to the Element component as part of the props object.

Q7: What is the Use of Refs?

Answer:
Refs provide a way to access DOM elements directly or interact with instances of a component. Refs are generally used for cases such as:

• Managing focus or text selection.
• Triggering animations.
• Integrating third-party libraries that require direct access to the DOM.

Refs are created using React.createRef() and assigned via the ref attribute.

Example:

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.myRef = React.createRef();
  }
  render() {
    return <div ref={this.myRef} />;
  }
}

Q8: How Would You Write an Inline Style in React?

Answer:
In React, you can apply inline styles by using the style attribute and passing an object with CSS properties as key-value pairs.

Example:

<div style={{ height: '10px' }}></div>

In this case, the style attribute is directly applying a height of 10 pixels to the div.

Q9: What is React?

Answer:
React is an open-source JavaScript library developed by Facebook, used to build interactive and dynamic user interfaces (UIs) for web and mobile applications. React is often referred to as the “V” (view) in the MVC (Model-View-Controller) architecture, allowing developers to efficiently manage the view layer.

Q10: What Are Inline Conditional Expressions in ReactJS?

Answer:
React allows you to conditionally render elements using JavaScript logic. You can use if statements or ternary operators to decide which components to render. Additionally, the && logical operator is commonly used in JSX to render components based on a condition.

Example:

{this.state.mode === 'view' ? (
  <button onClick={this.handleEdit}>Edit</button>
) : (
  <button onClick={this.handleSave}>Save</button>
)}

Q11: What Are Refs Used for in React?

Answer:
Refs provide direct access to DOM elements or a React component instance. They are often used for tasks like focusing on a specific input field or triggering an animation in an imperative way.

Example:

Practice Questions FAQ

To help you prepare further, here are some practice questions you can try on your own:

Beginner-Level Questions:

1. What is JSX, and how is it different from HTML?
2. How do you create a functional component in React?
3. What is the difference between state and props?
4. How do you handle events in React?
5. What is the significance of keys in React lists?

Intermediate-Level Questions:

6. How do you optimize performance in a React application?
7. What are Higher-Order Components (HOCs), and how do you use them?
8. How do you handle forms in React?
9. What is React Router, and how do you implement it?
10. How do you manage global state in React without using Redux?

Advanced-Level Questions:

11. What is the difference between useMemo and useCallback?
12. How do you implement code-splitting in React?
13. What are error boundaries, and how do you use them?
14. How do you test React components using Jest and React Testing Library?
15. What are the differences between class components and functional components?

Try solving these questions on your own, and refer to the official React documentation for detailed explanations.

Read More…

If you found this article helpful, check out our other posts on JavaScript, Node.js, and Data Structure to expand your knowledge and prepare for your next interview. Don’t forget to subscribe to our newsletter for the latest updates and tutorials!