Top 50 Reactjs Interview Questions

React.js has emerged as one of the most popular JavaScript libraries for building user interfaces, thanks to its efficient and flexible approach to front-end development. As React continues to gain prominence in the web development landscape, the demand for skilled React developers has soared. Whether you’re a seasoned React developer or just beginning your journey with the library, preparing for React.js interviews is essential to showcasing your expertise and securing coveted positions in the field.

In this guide, we’ve compiled a comprehensive list of the top 50 React.js interview questions to help you navigate the interview process with confidence. These questions cover a wide range of topics, including React fundamentals, component lifecycle, state management, hooks, and more. Whether you’re brushing up on your knowledge or diving deep into React concepts for the first time, this resource serves as a valuable tool to help you ace your React.js interviews.

From basic concepts to advanced techniques, each question is designed to test your understanding of React.js principles and best practices. By familiarizing yourself with these questions and their answers, you’ll be better equipped to tackle technical interviews, demonstrate your proficiency in React development, and land your dream job in the dynamic world of web development.

So, whether you’re gearing up for your first React.js interview or looking to level up your skills as a seasoned developer, dive into these top 50 React.js interview questions to sharpen your knowledge and excel in your next career opportunity.

Table of Content

  • What is React?
  • Explain JSX
  • What is the Virtual DOM?
  • What is the Significance of the keys in React?
  • What are state and props in React?
  • What is the difference between state and props?
  • Explain the concept of lifting state up.
  • What is the purpose of setState in React?
  • What is React Router?
  • Explain the useEffect hook.
  • What are controlled components in React?
  • What is Redux, and Why is it used?
  • Explain the concept of Higher-order components (HOC).
  • What is the purpose of the useReducer Hook?
  • What is the significance of the key attribute in React lists?
  • What is the difference between class components and functional components?
  • Explain the concept of refs in React
  • What are React Hooks?
  • Explain the purpose of the useContext hook.
  • What is the significance of the dangerouslySetInnerHTML property in React?

What is Reactjs?

React in an open-source JavaScript library for building user interfaces or UI components, developed by Facebook.

Explain JSX

JSX stands for JavaScript XML. JSX is a syntax extension for JavaScript recommended by React for describing What the UI should look like.

What is the Virtual DOM?

The Virtual DOM is a lightweight copy of the actual DOM in memory. React uses it to improve performance by updating only the changed parts of the actual DOM.

What is the Significance of Keys in React?

Keys are used to uniquely identify & differentiate between components in React. They help React identify which items have changed, added, or removed in the Application.

What are State & Props in React?

State is an Internal data store that belongs to specific components & it can be changed over time. Props are properties passed to components from its parent & they are immutable.

What is the difference between State and Props?

Stats is internal to a Component & can be changed over time, while Props are external and passed to a component.

Explain the concept of lifting state up.

Lifting state up is a pattern where the state of a child components is moved to its parent component, allowing multiple child components to share the same state.

What is the purpose of the setState in React?

setState is used to update the state of a component and trigger a re-render.

What is React Router?

React Router is a library that enables navigation among views in a React Application, allowing for the development of single-page applications.

Explain the useEffect hook.

The useEffect hook in React is used for side effects in function components, such as data fetching, subscriptions, or manually changing the DOM.

What are controlled Components in React?

Controlled components are components where the form data is controlled by React state. The input elements receive their current value from the state and have their value updated through a callback function.

What is Redux & Why is it Used?

Redux is a State management library for JavaScript applications, commonly used with React. It Helps manage the state of an application in a predictable way.

Explain the concept of higher-order components (HOC).

Higher-order components are functions that take a component and return a New component with additional features or props.

What is the purpose of the useReducer Hook?

The useReducer hook is used for managing complex state logic in React applications. It is an alternative to useState when state transitions are more complex.

What is the significance of the key attribute in React lists?

The key attributes are used to uniquely identify elements in a list. It helps React efficiently update the DOM when the list changes.

What is the difference between Class Components & Functional Components?

Class Components use ES6 classes and have While features like state and lifecycle methods, while Functional Components are simpler and are often used with Hooks.

Explain the Concept of Refs in React.

Refs are used to access the DOM directly or to reference a React element. They provide a way to interact with the underlying DOM nodes in React.

What are React Hook?

React Hooks are functions that allow functional components to use state, lifecycle methods & other React features.

Explain the purpose of the useContext Hook.

The useContext Hook is used to access the Value of a React Context within a functional component.

What is the Significance of the dangerouslySetHTML property in React?

dangerouslySetInnerHTML is used to inject HTML directly into a component, but it should be used with caution to avoid cress-side scripting (XSS) vulnerabilities.

What is the purpose of the componentDidMount lifecycle method?

componentDidMount is invoked immediately after a component is mounted, making it suitable for initial AJAX requests or setting up subscriptions.

What is the Reactjs Developer Tools?

The React Developer Tools is a browser extension that allows developers to inpect and debug React component hierarchies in the Chrome and Firefox browsers.

Explain the concept of context in Reactjs.

Context provides a way to pass data through the component tree without having to pass props manually at every level. It is often used to share values like themes or authentication status.

What are the Advantages of Using Reactjs?

React offers a virtual DOM for improved performance, a component-based architecture for modular development, and strong community support, among other advantages.

How does Reactjs Handle prop drilling, and How can it be avoided?

Prop Drilling occurs when props are passed down through multiple levels of components. It can be avoided by using context or state management libraries like Redux.

What is the purpose of the shouldComponentUpdate Method?

shouldComponentUpdate is a lifecycle method that determines if a component should re-render. Developers can use it to optimize performance by preventing unnecessary renders.

Explain the Significance of Reactjs Fragments.

Reactjs Fragments allows developers to group multiple elements without adding an extra node to the DOM, helping to keep the structure clean.

What is the significance of the key prop in Reactjs Router?

the key prop in Reactjs Router is used to force the remounting of a component when the key changes, ensuring that the component is fully reinitialized.

What is the purpose of the forwardRef function in Reactjs?

forwardRef is used to forward refs through components, allowing parent components to interact with the child’s DOM node.

Explain the concept of error boundaries in Reactjs.

Error boundaries are components that catch JavaScript errors anywhere in their child component tree and log those errors, display a fallback UI, or take other actions.

What is the significance of the memo functions in Reactjs?

memo is a higher-order component that memories the rendering of a functional component, preventing unnecessary re-renders if the props have not changed.

How does Reactjs handle forms?

Reactjs handles forms by using controlled components, where form data is controlled by the Reactjs state.

Explain the purpose of the useMemo Hook.

The useMemo Hook is used to memorize the result of a function, preventing unnecessary calculations an improving performance.

What is the significance of the useCallback Hook?

useCallback is used to memorize callback functions, preventing them from being recreated on every render.

What are Reactjs portals?

Reactjs portals provide a way to a render children into a DOM node that exists outside the parent component’s hierarchy.

Explain the concept of suspense in Reactjs.

Suspense is a feature in Reactjs that allows components to “wait” for something before rending, such as data fetching or code splitting.

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