React JS is one of the most popular JavaScript libraries for building user interfaces, especially for single-page applications. If you're preparing for a React JS interview at Accenture, this blog will help you get familiar with common interview questions and answers to showcase your knowledge of React concepts and best practices.
1. What is React, and why is it used?
React is a JavaScript library developed by Facebook for building fast, interactive user interfaces for web applications. It uses a component-based architecture, making code reusable and easier to maintain. React is used for handling the view layer of web and mobile apps.
2. What are the key features of React?
- JSX (JavaScript XML): Allows embedding HTML within JavaScript.
- Components: Building blocks of any React application.
- Virtual DOM: Boosts performance by reducing direct manipulation of the real DOM.
- One-Way Data Binding: Ensures that data flows in a single direction, improving control.
- Declarative UI: Makes code more predictable and easier to debug.
3. What is JSX, and how is it different from HTML?
JSX is a syntax extension for JavaScript, resembling HTML but allowing JavaScript expressions inside it. Unlike HTML, JSX needs to be transpiled by tools like Babel to convert it into valid JavaScript.
4. Can you explain the difference between state and props in React?
- State: A local data storage managed inside the component and can change over time.
- Props: Short for properties, props are passed from parent components to child components and are immutable.
5. What is the Virtual DOM, and how does it improve performance?
The Virtual DOM is a lightweight copy of the real DOM. Instead of updating the actual DOM immediately, React updates the Virtual DOM and compares it with the real DOM (a process known as reconciliation). Only the changed elements are updated in the real DOM, improving performance.
6. What are React components, and what types of components are there?
React components are the building blocks of a React application. There are two types:
- Class Components: ES6 classes that extend
React.Componentand have lifecycle methods. - Functional Components: Functions that take props and return JSX. They are simpler and easier to test, and with React Hooks, they can handle state and side effects.
7. What are React Hooks? Can you name some commonly used hooks?
Hooks are functions that allow you to use state and other React features in functional components. Common hooks include:
- useState(): For managing state.
- useEffect(): For side effects, such as fetching data or updating the DOM.
- useContext(): For consuming context in functional components.
8. Explain the useState() hook in React.
The useState hook is used to add state to functional components. It takes the initial state as an argument and returns an array containing the current state and a function to update the state.
const [count, setCount] = useState(0);
9. What is the useEffect() hook, and how is it used?
useEffect() is used for handling side effects in functional components. It runs after every render by default, but you can control it by passing a dependency array to specify when it should re-run.
useEffect(() => {
document.title = `Count is ${count}`;
}, [count]);
10. How do you optimize performance in React applications?
Performance optimization techniques include:
- Memoization: Using
React.memo()to prevent unnecessary re-renders. - Code Splitting: Dynamically loading components with
React.lazy()andSuspense. - Using Keys: Ensuring that list items have unique keys.
- Avoiding Inline Functions: Declaring functions outside render to prevent unnecessary re-creations.
11. What are controlled and uncontrolled components in React?
- Controlled Components: The form data is handled by the React component, with state controlling the input value.
- Uncontrolled Components: Form data is managed by the DOM itself, with a
refused to access the input value.
12. How do you handle events in React?
React handles events similarly to HTML but uses camelCase for event names (e.g., onClick instead of onclick). Event handlers can be passed as functions to elements.
<button onClick={handleClick}>Click Me</button>
13. Can you explain how the React Router works?
React Router is a standard library used for routing in React applications. It allows for declarative routing, enabling dynamic rendering of different components based on the URL.
<BrowserRouter>
<Route path="/" component={Home} />
<Route path="/about" component={About} />
</BrowserRouter>
14. What is Redux, and how does it manage state in React applications?
Redux is a predictable state container for JavaScript apps, often used with React for managing global application state. It follows three principles: single source of truth (state stored in a single object), state is read-only, and changes are made with pure functions called reducers.
15. How does Redux work with actions and reducers?
- Actions: Objects that send data from the application to the Redux store.
- Reducers: Pure functions that take the current state and an action and return the next state.
const reducer = (state = initialState, action) => {
switch (action.type) {
case 'INCREMENT':
return { count: state.count + 1 };
default:
return state;
}
};
16. What is the difference between Context API and Redux?
The Context API is a simpler solution for passing data through the component tree without having to manually pass props. Redux is more complex and provides features like middleware, making it better suited for larger applications with complex state management needs.
17. What are higher-order components (HOCs)?
HOCs are functions that take a component and return a new component. They allow code reusability and sharing of logic between components without modifying them directly.
const withLogger = (WrappedComponent) => {
return class extends React.Component {
componentDidMount() {
console.log('Component Mounted');
}
render() {
return <WrappedComponent {...this.props} />;
}
};
};
18. What is React Fiber, and how does it improve React's performance?
React Fiber is the new reconciliation algorithm in React 16, designed to enable incremental rendering of the virtual DOM. It breaks rendering work into chunks, allowing React to pause, prioritize, or reuse rendering work, resulting in improved performance.
19. How do you handle forms in React?
Handling forms in React involves using controlled components where the form data is managed via state. You can also handle form submission with an event handler.
const handleSubmit = (event) => {
event.preventDefault();
alert('Form Submitted');
};
20. How do you implement code splitting in a React application?
Code splitting in React can be achieved with React.lazy() and Suspense, which allow components to load on-demand, improving the app's performance.
const OtherComponent = React.lazy(() => import('./OtherComponent'));
21. What are React Fragments, and why are they used?
React Fragments let you group multiple elements without adding extra nodes to the DOM. This is useful when returning multiple elements from a component without wrapping them in a div.
<>
<ChildA />
<ChildB />
</>
22. How do you handle errors in a React application?
React 16 introduced Error Boundaries, which are components that catch JavaScript errors anywhere in their child component tree and display a fallback UI.
class ErrorBoundary extends React.Component {
componentDidCatch(error, info) {
// Log or handle the error
}
render() {
return this.props.children;
}
}
23. What is PropTypes in React, and how is it used?
PropTypes is a mechanism for checking the types of props passed to a component. It improves code quality by catching potential bugs during development.
MyComponent.propTypes = {
name: PropTypes.string,
age: PropTypes.number,
};
24. How do you debug a React application?
Debugging in React can be done using:
- React Developer Tools: Chrome/Firefox extension to inspect the component hierarchy.
- console.log(): Adding logs to trace errors.
- React Profiler: To analyze performance issues.
25. What is reconciliation in React?
Reconciliation is the process through which React updates the DOM. It involves comparing the new Virtual DOM with the previous one and updating only the changed elements in the real DOM.
26. How does lifting state up help in React applications?
Lifting state up involves moving the shared state to the closest common ancestor of the components that need access to it. This ensures that both components are updated with the same state and helps prevent duplication of logic.
27. What is the significance of keys in React lists?
Keys help React identify which items have changed, been added, or been removed. Keys should be unique among siblings to ensure that the UI is updated efficiently.
const listItems = items.map((item) => <li key={item.id}>{item.name}</li>);
28. How can you memoize a component in React?
You can use React.memo() to memoize a functional component. This prevents re-renders if the props remain the same, improving performance.
const MyComponent = React.memo((props) => {
return <div>{props.name}</div>;
});
29. How do you handle routing in a React application?
React Router allows you to handle routing by mapping components to different paths. It uses the BrowserRouter, Route, Link, and Switch components to enable navigation within a single-page application.
<BrowserRouter>
<Route exact path="/" component={Home} />
<Route path="/about" component={About} />
</BrowserRouter>
30. What are the benefits of server-side rendering (SSR) in React?
Server-side rendering improves performance by generating HTML on the server and sending it to the client. This reduces the time for the first contentful paint and enhances SEO by allowing search engines to crawl the rendered content.
Conclusion
These 30 React JS interview questions and answers will help you confidently face your Accenture interview. Ensure you understand each concept deeply, as it will allow you to provide clear and accurate responses in real interview situations.
Good luck!
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