10+ React Js Software Engineer Interview Questions and Answers

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

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

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.

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

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

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.

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

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.

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.

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

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

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