React Js Software Engineer
10+ React Js Software Engineer Interview Questions and Answers

Asked in UBS

Q. ES6 features Shallow cloning and deep cloning How to deep clone nested objects? Hoisting JS execution cycle - call stack, event loop and callbacks
ES6 features, shallow and deep cloning, hoisting, JS execution cycle.
ES6 features include arrow functions, template literals, let and const, destructuring, spread and rest operators, etc.
Shallow cloning creates a new object with the same properties as the original object. Deep cloning creates a new object with all nested objects also cloned.
To deep clone nested objects, use a recursive function or a library like lodash.
Hoisting is the behavior of moving variable and function ...read more

Asked in UBS

Q. What does strict mode do? Accessibility in react How forwardRef works? Keys in react controlled components, uncontrolled components, how to use those?
Explaining the features and usage of ReactJS
Strict mode catches common mistakes and enforces best practices
ForwardRef allows passing refs to child components
Keys help React identify which items have changed, added, or removed
Controlled components are stateful and rely on props to update, while uncontrolled components manage their own state
Accessibility in React involves using ARIA attributes and semantic HTML

Asked in NeoSOFT

Q. What are getStaticProps and getServerSideProps used for?
staticSideProps and serverSideProps are used in Next.js for data fetching and pre-rendering.
staticSideProps is used for pre-rendering static data at build time.
serverSideProps is used for pre-rendering dynamic data at request time.
staticSideProps is used for data that does not change frequently.
serverSideProps is used for data that changes frequently or needs to be fetched at request time.

Asked in NeoSOFT

Q. What is Server Side Rendering and Static Site Generation?
Server Side Rendering (SSR) is the process of rendering web pages on the server side before sending them to the client. Static Site Generation (SSG) is the process of generating static HTML files at build time.
SSR improves performance by reducing the time to first paint and providing better SEO.
SSR can be implemented using frameworks like Next.js in React.
SSG pre-renders pages at build time, resulting in faster loading times and improved SEO.
SSG is commonly used in static sit...read more

Asked in NeoSOFT

Q. What are fallbacks in getStaticPaths in Next.js?
Fallback in getStaticPaths in NextJs allows dynamic routes to be pre-rendered on-demand.
Fallback value can be true, false, or 'blocking'.
When fallback is true, Next.js will serve a static page for paths not generated at build time.
When fallback is 'blocking', Next.js will server a static page for paths not generated at build time, but will also server-render the page on the first request.
Fallback is useful for dynamic routes with a large number of possible values.

Asked in NeoSOFT

Q. What is the nextHat package used for in Next.js?
nextHat package in NextJs is used for server-side rendering and managing server-side logic.
nextHat package helps in handling server-side logic in NextJs applications
It allows for server-side rendering of pages in NextJs
nextHat package can be used for managing API calls and server-side data fetching
React Js Software Engineer Jobs




Asked in NeoSOFT

Q. What is dynamic Import in NextJs?
Dynamic Import in NextJs allows for code splitting and loading components only when needed.
Dynamic Import in NextJs is a feature that allows you to import components asynchronously, improving performance by loading components only when needed.
It helps in code splitting, where different parts of the application can be loaded separately, reducing the initial load time.
Dynamic Import is achieved using the dynamic import() function in NextJs.
Example: const MyComponent = dynamic((...read more

Asked in Inara Consultancy Services

Q. Create a stopwatch in React.
Create a stopwatch in React using state and lifecycle methods.
Use state to store the current time and whether the stopwatch is running.
Use lifecycle methods like componentDidMount and componentWillUnmount to start and stop the stopwatch.
Use setInterval to update the time every second.
Display the time in a user-friendly format like HH:MM:SS.
Share interview questions and help millions of jobseekers 🌟

Asked in UBS

Q. React testing How to test hooks?
Hooks can be tested using React Testing Library or Enzyme.
Use React Testing Library's renderHook() method to test hooks
Test the hook's return value and its behavior on re-renders
Use Enzyme's shallow() or mount() methods to test hooks
Mock any external dependencies used in the hook
Test edge cases and error handling

Asked in NeoSOFT

Q. What are PWAs?
PWA's are Progressive Web Applications that use modern web capabilities to provide a user experience similar to native mobile apps.
PWA's can work offline or on low-quality networks.
They can be installed on the user's device like a native app.
PWA's are built using web technologies like HTML, CSS, and JavaScript.
Examples of PWA's include Twitter Lite, Pinterest, and Starbucks.

Asked in Cognizant

Q. What is the virtual DOM?
Virtual DOM is a lightweight copy of the actual DOM that React uses to improve performance by minimizing direct manipulation of the actual DOM.
Virtual DOM is a concept in React where a lightweight copy of the actual DOM is created and updated in memory.
When changes are made to the virtual DOM, React compares it with the actual DOM and only updates the necessary parts, reducing the number of direct manipulations to the actual DOM.
This helps improve performance by minimizing th...read more

Asked in Infosys

Q. What is useEffect?
useEffect is a hook in React that allows performing side effects in function components.
useEffect is used to perform side effects in function components.
It runs after every render by default.
It can be used to fetch data, subscribe to events, or update the DOM.
It can also clean up effects from previous renders.
It takes two arguments: a function and an optional array of dependencies.

Asked in Genpact

Q. What is Reconciliation?
Reconciliation is the process of updating the UI to match the current state of the application.
Reconciliation is the algorithm used by React to update the DOM efficiently.
It compares the virtual DOM with the actual DOM and only updates the parts that have changed.
Reconciliation is a key feature of React that helps in optimizing performance.
Examples include adding, removing, or updating elements in a list without re-rendering the entire list.

Asked in NeoSOFT

Q. Eager loading Vs Lazy loading?
Eager loading loads all related data upfront, while lazy loading loads data only when needed.
Eager loading is more efficient for small datasets or when all related data is needed at once.
Lazy loading is better for large datasets or when only specific data is needed.
Eager loading can lead to performance issues if unnecessary data is loaded, while lazy loading can cause additional queries to be made.
Examples: Eager loading in React can be achieved using libraries like Redux, wh...read more

Asked in IMPACT Infotech

Q. What are the differences between useMemo and React.memo?
useMemo is a hook used for memoization of expensive calculations, while react.memo is a higher order component used for memoizing functional components.
useMemo is used to memoize expensive calculations and can be used inside functional components.
react.memo is used to memoize functional components to prevent unnecessary re-renders.
useMemo returns a memoized value, while react.memo returns a memoized component.
Example: useMemo can be used to memoize the result of a complex com...read more
Interview Questions of Similar Designations
Interview Experiences of Popular Companies






Calculate your in-hand salary
Confused about how your in-hand salary is calculated? Enter your annual salary (CTC) and get your in-hand salary


Reviews
Interviews
Salaries
Users

