Meta React JS Interview Questions

Meta React JS Interview Questions

On December 8, 2025, Posted by , In Reactjs, With Comments Off on Meta React JS Interview Questions
Meta React JS Interview Questions

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As I embark on my journey to secure a role at Meta, I know that mastering React JS is essential to stand out in a highly competitive landscape. The Meta React JS Interview Questions dive deep into both the technical and behavioral aspects of candidates. They often focus on JavaScript, TypeScript, and React fundamentals, challenging my understanding of component lifecycles, hooks, state management, and performance optimization. By preparing for questions that range from theoretical concepts to hands-on coding challenges, I can showcase my ability to build high-quality applications effectively.

To bolster my preparation for the upcoming Meta React JS interview, I’m committed to exploring a variety of potential questions that could arise during the process. This guide on Meta React JS Interview Questions will serve as a roadmap, helping me understand what to expect and how to respond confidently. Additionally, I’ve discovered that React developers at Meta enjoy attractive salaries, averaging between $120,000 and $180,000 annually, which adds to my motivation. With this comprehensive content, I’m ready to enhance my skills and increase my chances of landing a coveted position at one of the leading tech giants.

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1. What is the significance of React’s virtual DOM?

The significance of React’s virtual DOM lies in its ability to optimize performance and enhance the user experience. When I create a user interface in React, it maintains a lightweight copy of the actual DOM in memory. This virtual DOM allows React to efficiently determine which parts of the UI need to be updated when the state changes. Instead of directly manipulating the real DOM, React first updates the virtual DOM, then compares it with the previous version to identify changes. This process is known as “diffing.”

By using the virtual DOM, React minimizes the number of direct manipulations to the actual DOM, which is often slow and resource-intensive. For example, consider a scenario where I have a large list of items that need to be updated. Instead of re-rendering the entire list, React can update only the items that have changed, significantly improving performance. The virtual DOM’s efficiency means that I can build dynamic and responsive applications without worrying about performance bottlenecks.

See also: Amazon Angular JS interview Questions

2. How does React handle reconciliation?

Reconciliation is a crucial process in React that determines how the UI is updated efficiently when the state or props change. When I update the state of a component, React uses the virtual DOM to identify what has changed. It performs a “diffing” algorithm to compare the newly rendered virtual DOM with the previous one. This algorithm is optimized to quickly find differences and determine the minimal set of changes needed to update the actual DOM.

I appreciate that React prioritizes performance during reconciliation. For instance, React uses keys to identify which items have changed, been added, or removed in lists. By assigning unique keys to elements, I help React optimize its rendering process.

Here’s a simple example:

const ListItem = ({ item }) => <li>{item}</li>;

const ItemList = ({ items }) => {
    return (
        <ul>
            {items.map(item => (
                <ListItem key={item.id} item={item.name} />
            ))}
        </ul>
    );
};

In this example, each list item has a unique key (item.id), allowing React to efficiently reconcile changes in the list.

See also: React JS Interview Questions for 5 years Experience

3. Can you explain the concept of “lifting state up” in React?

The concept of “lifting state up” in React refers to the practice of moving state from child components to a common parent component. I often find myself in situations where multiple child components need access to the same state data. Instead of maintaining separate state instances in each child, I can lift the state up to the nearest common ancestor. This approach promotes better state management and ensures that all child components can access and update the same state.

When I lift state up, I pass the state and any necessary functions down to the child components as props. This enables the child components to read the state and invoke functions to update it while the parent component holds the actual state. For example:

const ParentComponent = () => {
    const [count, setCount] = useState(0);

    return (
        <div>
            <ChildComponent count={count} setCount={setCount} />
        </div>
    );
};

const ChildComponent = ({ count, setCount }) => {
    return (
        <div>
            <p>Count: {count}</p>
            <button onClick={() => setCount(count + 1)}>Increment</button>
        </div>
    );
};

In this example, the ParentComponent lifts the count state and the setCount function up, allowing ChildComponent to access and modify the count state. By doing this, I maintain a single source of truth, making it easier to manage the flow of data and keep the UI in sync.

See also: Basic React JS Interview Questions for beginners

4. What are the differences between controlled and uncontrolled components?

In React, the primary difference between controlled and uncontrolled components lies in how they manage form data. A controlled component has its form data managed by React through state. This means that I control the input value through the component’s state, making it easier to implement features like validation or conditional rendering. For example, when I use a controlled input, I set its value with a state variable and update that variable on each change event.

import React, { useState } from 'react';

const ControlledInput = () => {
    const [value, setValue] = useState('');

    const handleChange = (e) => {
        setValue(e.target.value);
    };

    return (
        <input type="text" value={value} onChange={handleChange} />
    );
};

In the above example, the input field is controlled by the value state, which is updated with each keystroke. This allows me to maintain full control over the input.

On the other hand, an uncontrolled component manages its own state internally using the DOM. In this case, I can directly access the input value using a ref instead of storing it in the component’s state. Here’s how an uncontrolled component looks:

import React, { useRef } from 'react';

const UncontrolledInput = () => {
    const inputRef = useRef(null);

    const handleSubmit = (e) => {
        e.preventDefault();
        alert('Input value: ' + inputRef.current.value);
    };

    return (
        <form onSubmit={handleSubmit}>
            <input type="text" ref={inputRef} />
            <button type="submit">Submit</button>
        </form>
    );
};

In this uncontrolled example, I use a ref to access the input value directly. While this can be simpler for quick implementations, I’ve noticed that uncontrolled components can make it more challenging to track and manage form data effectively. Therefore, for applications that require more control and consistency, I typically prefer controlled components.

See also: Lifecycle Methods in React JS Interview Questions

5. How does React handle events differently from native JavaScript events?

React handles events differently from native JavaScript events by utilizing a synthetic event system. This system is designed to normalize events across different browsers, ensuring consistent behavior. When I use event handlers in React, I can directly pass them as props to components without worrying about cross-browser discrepancies. This is one of the reasons I appreciate working with React, as it simplifies event handling.

Another significant difference is that React uses the event delegation approach. Instead of attaching event listeners to each individual element, React attaches a single event listener to the root of the component hierarchy. When an event occurs, it bubbles up through the component tree, allowing React to efficiently manage events without needing to bind listeners for every element. For example:

const Button = ({ handleClick }) => {
    return <button onClick={handleClick}>Click Me!</button>;
};

const App = () => {
    const handleClick = (e) => {
        console.log('Button clicked:', e.target);
    };

    return (
        <div>
            <Button handleClick={handleClick} />
        </div>
    );
};

In this example, I define an event handler in the App component and pass it to the Button component as a prop. This keeps the event management centralized and straightforward, allowing for better performance, especially in applications with many interactive elements.

See also: Data Binding in AngularJS Interview Questions

6. What are the advantages of using React’s context API?

One of the key advantages of using React’s context API is its ability to simplify state management in larger applications. When I have multiple components that need to share the same data or state, using props can become cumbersome and lead to “prop drilling,” where I have to pass props through many layers of components. The context API allows me to create a global state that can be accessed by any component in the tree without needing to pass props explicitly.

Here’s a simple example of how to set up and use context:

import React, { createContext, useContext, useState } from 'react';

const ThemeContext = createContext();

const ThemeProvider = ({ children }) => {
    const [theme, setTheme] = useState('light');

    return (
        <ThemeContext.Provider value={{ theme, setTheme }}>
            {children}
        </ThemeContext.Provider>
    );
};

const ThemedComponent = () => {
    const { theme, setTheme } = useContext(ThemeContext);
    
    return (
        <div style={{ background: theme === 'light' ? '#fff' : '#333', color: theme === 'light' ? '#000' : '#fff' }}>
            <p>The current theme is {theme}.</p>
            <button onClick={() => setTheme(theme === 'light' ? 'dark' : 'light')}>
                Toggle Theme
            </button>
        </div>
    );
};

In this example, I create a ThemeContext to share the theme state across components. The ThemedComponent uses the useContext hook to access the theme and the function to update it. This approach reduces the need for prop drilling and keeps my code organized.

Additionally, the context API promotes better organization and scalability. I can create separate context providers for different pieces of state, which helps keep my code modular and easier to manage. However, I always ensure that I don’t overuse the context API, as it can make debugging more complex if not used judiciously.

See also: Flipkart Angular JS interview Questions

7. How does server-side rendering (SSR) work in React?

Server-side rendering (SSR) in React involves rendering a React application on the server rather than in the browser. This process generates the initial HTML of the application on the server and sends it to the client, allowing users to see the content immediately without waiting for the JavaScript to load. I find this approach particularly beneficial for improving the performance of my applications and enhancing SEO.

To implement SSR in React, I typically use frameworks like Next.js or Gatsby, which provide built-in support for SSR.

Here’s a basic example of how SSR works using Next.js:

// pages/index.js
const Home = ({ data }) => {
    return (
        <div>
            <h1>Server-Side Rendered Page</h1>
            <p>{data}</p>
        </div>
    );
};

export async function getServerSideProps() {
    const res = await fetch('https://api.example.com/data');
    const data = await res.json();

    return {
        props: {
            data: data.message,
        },
    };
}

export default Home;

In this example, the getServerSideProps function fetches data from an API before the page is rendered. This data is then passed as props to the Home component, which renders the content on the server. When the client receives the HTML, it already contains the data, improving the perceived load time and enabling better SEO since search engines can crawl the content.

8. Can you explain the concept of “higher-order components” (HOCs)?

Higher-order components (HOCs) are a powerful pattern in React that involves creating a function that takes a component as an argument and returns a new component with additional props or behavior. HOCs are often used for code reuse, logic abstraction, and enhancing components with additional functionalities.

For instance, an HOC can be used to add authentication logic to a component:

const withAuth = (WrappedComponent) => {
    return (props) => {
        const isAuthenticated = checkAuthentication(); // hypothetical function
        return isAuthenticated ? <WrappedComponent {...props} /> : <Redirect to="/login" />;
    };
};

// Usage
const ProtectedComponent = withAuth(MyComponent);

In this example, withAuth checks the authentication status before rendering MyComponent. If the user is authenticated, it renders the wrapped component; otherwise, it redirects to the login page. This approach allows me to encapsulate authentication logic in one place and apply it to multiple components.

See also: Full Stack developer Interview Questions

9. What are the trade-offs between using React with TypeScript versus plain JavaScript?

Using TypeScript with React offers several benefits and trade-offs compared to plain JavaScript:

Benefits:

Type Safety: TypeScript helps catch type-related errors during development, making the codebase more robust and reducing runtime errors.
Enhanced IDE Support: With TypeScript, I get better autocompletion, navigation, and refactoring capabilities in my IDE, improving developer productivity.
Improved Documentation: Type annotations serve as documentation, making it easier for other developers to understand component props and state.

Trade-offs:

Learning Curve: Developers need to learn TypeScript’s syntax and type system, which can add complexity for those unfamiliar with it.
Increased Initial Setup: Setting up a React project with TypeScript may require more configuration compared to a plain JavaScript project.
Compilation Step: TypeScript requires a compilation step to convert TypeScript code into JavaScript, which can slow down the development process compared to using plain JavaScript directly.

Overall, while TypeScript adds some overhead, its benefits in terms of type safety and improved developer experience often outweigh the drawbacks, especially in larger codebases.

10. How does React’s diffing algorithm improve performance?

React’s diffing algorithm (also known as reconciliation) optimizes performance by minimizing the number of updates made to the actual DOM. Here’s how it works:

1. Virtual DOM: React maintains a lightweight representation of the DOM in memory called the virtual DOM. When the state of a component changes, React creates a new virtual DOM tree.
2. Diffing Process: React compares the new virtual DOM tree with the previous one to identify changes.
This Diffing process involves:
Element Type Comparison: React checks if the elements are of the same type. If they are, it proceeds to compare their attributes.
Key Comparison: For lists of elements, React uses keys to identify which items have changed, been added, or removed.
3. Batch Updates: After identifying the differences, React batches updates and applies them to the real DOM in a single operation. This reduces the number of direct manipulations to the DOM, which are expensive in terms of performance.

By efficiently updating only the parts of the DOM that have changed, React significantly improves performance, especially in applications with complex UIs and frequent updates.

See also: Infosys FullStack Developer Interview Questions

11. What are prop types, and why are they useful in React?

Prop types are a feature in React that allows developers to define the types of props a component should receive. This is achieved using the prop-types library, which helps in validating the data types and shapes of props passed to a component.

Here’s an example of how to use prop types:

import PropTypes from 'prop-types';

const MyComponent = ({ name, age }) => (
    <div>
        <h1>{name}</h1>
        <p>Age: {age}</p>
    </div>
);

MyComponent.propTypes = {
    name: PropTypes.string.isRequired,
    age: PropTypes.number.isRequired,
};

Why are Prop Types Useful?

Validation: Prop types validate the props passed to a component, helping catch bugs and errors early in development.
Documentation: They serve as a form of documentation, making it easier for other developers to understand what data a component expects.
Runtime Checks: Prop types provide runtime checks for prop values, ensuring they conform to the specified types during development.

While Prop Types are not a replacement for TypeScript, they are a lightweight alternative for type checking in JavaScript applications.

See also: Deloitte Senior Developer Interview Questions

12. How do you handle error boundaries in a React application?

Error boundaries are components that catch JavaScript errors in their child component tree and render a fallback UI instead of crashing the entire application. I can implement error boundaries using the componentDidCatch lifecycle method and getDerivedStateFromError method.

Here’s an example:

class ErrorBoundary extends React.Component {
    constructor(props) {
        super(props);
        this.state = { hasError: false };
    }

    static getDerivedStateFromError(error) {
        // Update state to display fallback UI
        return { hasError: true };
    }

    componentDidCatch(error, errorInfo) {
        // Log error to an error reporting service
        console.error("Error caught by Error Boundary: ", error, errorInfo);
    }

    render() {
        if (this.state.hasError) {
            return <h1>Something went wrong.</h1>;
        }
        return this.props.children; 
    }
}

// Usage
<ErrorBoundary>
    <MyComponent />
</ErrorBoundary>

In this example, if any child component throws an error, the ErrorBoundary component will catch it and display a fallback UI (in this case, an error message). This prevents the entire app from crashing and provides a better user experience.

13. What is the significance of keys in lists of elements?

Keys are unique identifiers that React uses to identify which elements in a list have changed, been added, or removed. Keys help optimize the rendering performance of lists by enabling React to determine which components need to be re-rendered.

Importance of Keys:

Identity: Keys provide a stable identity for each element, allowing React to track elements across renders. This is crucial for efficient updates, especially in dynamic lists.
Performance Optimization: When keys are correctly implemented, React can minimize re-renders by reusing existing components rather than recreating them. This results in better performance, especially in large lists.
Avoiding Issues: Using the index of an array as a key can lead to issues with component state and behavior when items are reordered or removed. Instead, I should use unique identifiers (e.g., database IDs) whenever possible.

Here’s an example of using keys in a list:

const items = ['Apple', 'Banana', 'Cherry'];
const listItems = items.map((item) => <li key={item}>{item}</li>);

In this case, each list item has a unique key, enabling React to efficiently manage the list.

14. Can you explain the concept of “render props”?

Render props is a pattern for sharing code between React components using a prop that is a function. This function returns a React element and allows for more flexible and reusable components.

Here’s an example of a component that uses the render props pattern:

const DataProvider = ({ render }) => {
    const data = fetchData(); // hypothetical data fetching function
    return render(data);
};

// Usage
<DataProvider render={(data) => <DisplayComponent data={data} />} />

In this example, DataProvider fetches data and uses the render prop to pass the data to DisplayComponent. This allows DataProvider to share its logic while keeping the rendering flexible.

Benefits of Render Props:

Reusability: I can create components that encapsulate specific logic while allowing consumers to define how to render the output.
Decoupling Logic from Presentation: This pattern separates data logic from presentation, leading to cleaner and more maintainable code.
Dynamic Rendering: Render props allow for dynamic rendering based on the current state or props.

See also: Tech Mahindra FullStack Developer Interview Questions

15. What are some common patterns for state management in React applications?

There are several patterns for managing state in React applications, including:

1. Local State Management: I can use the built-in useState hook for local state management within functional components. This is suitable for simple state management needs.

2. Context API: React’s Context API allows me to create a global state that can be accessed by multiple components without prop drilling. This is useful for themes, user authentication, and other global settings.

const ThemeContext = React.createContext();

const App = () => {
    const [theme, setTheme] = useState('light');
    
    return (
        <ThemeContext.Provider value={{ theme, setTheme }}>
            <ChildComponent />
        </ThemeContext.Provider>
    );
};

3. Redux: Redux is a popular state management library for managing complex state in larger applications. It follows a unidirectional data flow and helps centralize application state. I can use middleware like Redux Thunk or Redux Saga for handling side effects.

4. MobX: MobX is another state management library that uses observables for state management. It provides a more flexible and less boilerplate-heavy approach than Redux.

5. Recoil: Recoil is a relatively new state management library that integrates well with React. It allows for fine-grained control of state and provides a simple API for managing state across components.

Choosing the right state management pattern depends on the complexity and requirements of the application.

16. How do you optimize the performance of a React application?

To optimize the performance of a React application, I can employ several strategies:

1. Memoization: Using React.memo for functional components and PureComponent for class components helps prevent unnecessary re-renders by shallowly comparing props.

2. Code Splitting: I can use dynamic imports and React.lazy to load components only when needed. This reduces the initial bundle size, improving load times.

const LazyComponent = React.lazy(() => import('./LazyComponent'));

const App = () => (
    <React.Suspense fallback={<div>Loading...</div>}>
        <LazyComponent />
    </React.Suspense>
);

3. Use of Keys: As mentioned earlier, using keys correctly in lists helps React optimize rendering.

4. Avoid Inline Functions and Objects: Inline functions and objects in props can cause unnecessary re-renders. I should define them outside the render method or use useCallback and useMemo hooks for memoization.

5. Optimize Context Usage: When using Context API, ensure that only components that need to re-render on state changes do so by separating contexts or using multiple contexts.

6. Use Production Build: Always ensure I’m serving a production build of my application, as it is optimized for performance.

By implementing these optimizations, I can significantly enhance the performance of a React application, ensuring a smoother user experience.

See also: Tech Mahindra React JS Interview Questions

17. What role do third-party libraries play in the React ecosystem?

Third-party libraries play a significant role in the React ecosystem by providing additional functionalities, enhancing the development experience, and speeding up the development process. Here are some key areas where third-party libraries are commonly used:

1. State Management: Libraries like Redux, MobX, and Recoil help manage complex application states, providing structured approaches to state management beyond React’s built-in capabilities.

2. Routing: Libraries like React Router enable dynamic routing in React applications, making it easy to handle navigation and rendering of different components based on the URL.

3. Form Handling: Libraries such as Formik and React Hook Form simplify form management, including validation, submission handling, and state management.

4. UI Component Libraries: Libraries like Material-UI, Ant Design, and Bootstrap provide pre-built components that follow design guidelines, enabling faster UI development.

5. Data Fetching: Libraries like Axios and React Query help simplify API requests and manage server state, making data fetching more efficient and easier to handle.

6. Testing Utilities: Libraries like Jest, React Testing Library, and Enzyme provide tools for writing and executing tests, ensuring the application behaves as expected.

Using third-party libraries allows me to leverage community-driven solutions, saving time and effort while enhancing the capabilities of my React applications. However, it’s essential to evaluate the performance, size, and maintenance of these libraries to ensure they fit the project’s needs.

18. How does React Router enhance the navigation experience in single-page applications?

React Router is a powerful library that enables dynamic routing in single-page applications (SPAs). It enhances the navigation experience by providing a seamless and efficient way to manage views and routes without full page reloads.

Here are some key benefits:

Declarative Routing: With React Router, I can define routes declaratively using JSX syntax. This makes it easy to visualize the structure of my application and manage routing logic.

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';

const App = () => (
    <Router>
        <Switch>
            <Route path="/" exact component={Home} />
            <Route path="/about" component={About} />
            <Route path="/contact" component={Contact} />
        </Switch>
    </Router>
);

Dynamic Route Matching: React Router allows me to define dynamic routes that can match varying URL patterns. This is useful for displaying different components based on URL parameters.
Nested Routes: I can create nested routes to structure my application logically. This enables components to have their own child routes, making it easier to manage complex layouts.
Navigation Components: React Router provides built-in components like Link and NavLink for navigation, making it simple to create links between routes while maintaining the SPA experience.
History Management: It handles browser history management, allowing users to navigate using the back and forward buttons seamlessly.

By utilizing React Router, I can create a smooth and intuitive navigation experience for users, enhancing the overall usability of my application.

See also: Amazon React JS Interview Questions

19. What are some best practices for structuring a React application?

Structuring a React application effectively is crucial for maintainability and scalability. Here are some best practices:

1. Organize by Feature: Structure your folders and files based on features rather than file types. Each feature folder should contain all relevant components, styles, and tests, making it easier to manage and reason about.

2. Use Components Wisely: Break down the UI into reusable components. Each component should have a single responsibility, promoting reusability and easier testing.

3. Maintain a Clear State Management Strategy: Decide on a state management approach (like Redux, Context API, or local state) early on and keep your state centralized when necessary.

4. Follow Naming Conventions: Consistent naming conventions help improve code readability. Use clear and descriptive names for files, folders, and components.

5. Utilize a CSS Methodology: Use a CSS methodology like BEM or CSS Modules to manage styles. This helps prevent class name collisions and keeps styles organized.

6. Implement Routing Early: If your application requires routing, set it up from the beginning to keep your structure aligned with navigation needs.

7. Document Your Code: Maintain clear documentation and comments to explain complex logic, making it easier for others (or future you) to understand the codebase.

By following these best practices, I can create a well-structured React application that is easier to maintain and scale as it grows.

20. How do you ensure accessibility in your React components?

Ensuring accessibility in React components is crucial for creating inclusive applications. Here are some strategies to follow:

1. Semantic HTML: Use semantic HTML elements (e.g., <header>, <nav>, <main>, <footer>, <article>) to provide meaningful structure to the content. This helps screen readers understand the layout of the page.

2. ARIA Attributes: Implement ARIA (Accessible Rich Internet Applications) attributes when necessary to enhance accessibility for dynamic content. For example, use aria-live for notifications or aria-expanded for toggle buttons.

3. Keyboard Navigation: Ensure that all interactive elements are accessible via keyboard navigation. Use tabIndex to manage focus and ensure that custom components behave like native HTML elements.

4. Color Contrast: Check color contrast ratios to ensure that text is readable against its background. Tools like the WebAIM Contrast Checker can help assess color contrast.

5. Focus Management: Manage focus appropriately, especially when displaying modal dialogs or transitioning between pages. Set focus to the first interactive element in a modal when it opens.

6. Form Accessibility: Label all form inputs clearly with <label> elements and associate them using the htmlFor attribute. Provide descriptive error messages for validation.

7. Testing Tools: Use accessibility testing tools like aXe or Lighthouse to evaluate the accessibility of your components and identify areas for improvement.

By implementing these strategies, I can ensure that my React components are accessible to all users, including those with disabilities.

See also: React Redux Interview Questions And Answers

21. Can you explain how to implement code splitting in a React application?

Code splitting is a technique used to optimize the performance of a React application by splitting the code into smaller bundles that can be loaded on demand. This helps reduce the initial load time of the application. Here’s how to implement code splitting using React’s built-in features:

1. Dynamic Imports: Use dynamic imports to load components lazily. This is typically done with the React.lazy() function and Suspense component.

Here’s an example:

import React, { Suspense } from 'react';

const LazyComponent = React.lazy(() => import('./LazyComponent'));

const App = () => (
    <Suspense fallback={<div>Loading...</div>}>
        <LazyComponent />
    </Suspense>
);

In this example, LazyComponent will be loaded only when it is needed, improving the performance of the initial render.

2. React Router Integration: Code splitting can also be integrated with React Router to load route components lazily. For example:

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';

const Home = React.lazy(() => import('./Home'));
const About = React.lazy(() => import('./About'));

const App = () => (
    <Router>
        <Suspense fallback={<div>Loading...</div>}>
            <Switch>
                <Route path="/" exact component={Home} />
                <Route path="/about" component={About} />
            </Switch>
        </Suspense>
    </Router>
);

3.Third-Party Libraries: Libraries like react-loadable can also be used for more advanced code-splitting strategies. They provide a more customizable way to load components and manage loading states.

See also: Deloitte Angular JS Developer interview Questions

22. What is the purpose of React.memo, and how does it work?

React.memo is a higher-order component that optimizes the performance of functional components by preventing unnecessary re-renders. It does this by memoizing the component, meaning it will only re-render when its props change.

Purpose of React.memo:

Performance Optimization: It helps optimize functional components by avoiding re-renders when the props remain the same, reducing the rendering workload.

How It Works:

When a component wrapped in React.memo receives new props, React performs a shallow comparison of the previous and next props.
If the props have not changed, React will skip the re-render and return the last rendered output.

Here’s an example:

const MyComponent = React.memo(({ name }) => {
    console.log("Rendering:", name);
    return <div>{name}</div>;
});

// Usage
<MyComponent name="John" />

In this example, if the name prop does not change, MyComponent will not re-render, even if its parent component renders multiple times.

Custom Comparison:

React.memo also allows for a custom comparison function if I need to compare complex props. This function should return true if the props are equal (thus preventing re-render) and false otherwise.

const MyComponent = React.memo(
    ({ data }) => {
        // Component logic
    },
    (prevProps, nextProps) => {
        return prevProps.data.id === nextProps.data.id; // Custom comparison
    }
);

Using React.memo effectively can lead to performance improvements, especially in components that receive complex objects or are part of larger, frequently updating components.

See also: Accenture Angular JS interview Questions

23. How can you manage global state in a React application?

Managing global state in a React application can be achieved through various methods. Here are some common approaches:

1. Context API: The built-in Context API is a lightweight solution for managing global state. It allows me to create a context and provide it to the component tree, enabling any child component to access the state. Example:

const GlobalStateContext = React.createContext();

const GlobalStateProvider = ({ children }) => {
    const [state, setState] = useState(initialState);
    return (
        <GlobalStateContext.Provider value={{ state, setState }}>
            {children}
        </GlobalStateContext.Provider>
    );
};

// Usage in a component
const MyComponent = () => {
    const { state, setState } = useContext(GlobalStateContext);
};

2. Redux: Redux is a popular state management library that provides a centralized store for managing global state. It uses a unidirectional data flow and encourages a predictable state structure through actions and reducers. Example:

const initialState = { count: 0 };

const reducer = (state = initialState, action) => {
    switch (action.type) {
        case 'INCREMENT':
            return { count: state.count + 1 };
        default:
            return state;
    }
};

const store = createStore(reducer);

3. MobX: MobX is another state management library that provides a reactive programming model. It allows me to create observable state, and components automatically re-render when observables change.

4. Recoil: Recoil is a modern state management library designed for React applications. It offers a more flexible and intuitive API for managing global state and allows for derived state and asynchronous queries.

5. Jotai: Jotai is a minimalistic state management library that uses atoms to represent state. It provides a straightforward API for managing global state without the boilerplate associated with Redux.

Choosing the right approach depends on the complexity of the application and personal preferences. For smaller applications, the Context API may be sufficient, while larger applications may benefit from using Redux or Recoil for better state management.

See more: TCS AngularJS Developer Interview Questions

24. What are some common challenges you may face when testing React components?

Testing React components is essential for ensuring application reliability and functionality. However, it can present several challenges:

1. Asynchronous Code: Many React components rely on asynchronous operations (like data fetching). Testing components that involve promises, async/await, or timers can be challenging and may require tools like act to manage updates.
2. Component State Management: Components with complex state management may be difficult to test. Understanding how to simulate state changes and testing various states can be cumbersome.
3. Mocking Dependencies: When components depend on external libraries or APIs, mocking these dependencies is essential. This can become complicated, especially if the dependencies have intricate behavior or state.
4. Props and Context: Testing components that rely heavily on props or context can be challenging. Setting up the necessary context or providing the right props for tests may require additional setup.
5. Snapshot Testing: While snapshot testing is a useful feature, it can lead to fragile tests if overused. Changes in the component’s structure can cause frequent updates to snapshots, making it difficult to determine if the component behaves correctly.
6. Testing User Interactions: Simulating user interactions (clicks, form submissions) may require additional tools or libraries, such as React Testing Library. Understanding how to effectively simulate these interactions can be a challenge.
7. Performance Concerns: Large components or applications may lead to performance issues during testing, especially if tests are not well-optimized.

To mitigate these challenges, I can adopt a comprehensive testing strategy that combines unit testing, integration testing, and end-to-end testing, using libraries like Jest and React Testing Library. Writing clear, focused tests and using proper mocking techniques can also help alleviate these issues.

See also: Infosys AngularJS Interview Questions

25. How does the React lifecycle differ between class components and functional components with hooks?

The React lifecycle varies significantly between class components and functional components that utilize hooks. Here’s a breakdown of the differences:

Class Components:

Lifecycle Methods: Class components have specific lifecycle methods that can be overridden to perform actions at different points in a component’s life cycle. Key methods include:

componentDidMount: Invoked immediately after a component is mounted.
componentDidUpdate: Called after updates are flushed to the DOM.
componentWillUnmount: Invoked immediately before a component is unmounted and destroyed.

Example:

class MyComponent extends React.Component {
    componentDidMount() {
        // Fetch data or set up subscriptions
    }

    componentDidUpdate(prevProps) {
        // Respond to prop changes
    }

    componentWillUnmount() {
        // Clean up subscriptions
    }
}

Functional Components with Hooks:

1. useEffect Hook: Functional components use the useEffect hook to manage side effects, combining the functionalities of componentDidMount, componentDidUpdate, and componentWillUnmount into a single API.

Example:

const MyComponent = () => {
    useEffect(() => {
        // Fetch data or set up subscriptions

        return () => {
            // Clean up subscriptions
        };
    }, []); // Dependency array controls when the effect runs
};

2. Multiple Effects: In functional components, I can have multiple useEffect hooks to handle different side effects separately, providing a more granular approach to managing lifecycle events.

3. No this Keyword: Unlike class components, functional components do not use the this keyword, making the code cleaner and easier to read.

In summary, class components use specific lifecycle methods to manage the component lifecycle, while functional components with hooks rely on useEffect for side effects, leading to a more flexible and concise approach to managing component lifecycles.

See also: Accenture Java interview Questions and Answers

Conclusion

Preparing for Meta React JS Interview Questions is more than just a job search; it’s an opportunity to refine my skills and enhance my understanding of one of the most popular front-end libraries in the industry. By delving into essential concepts like the virtual DOM, state management, and the component lifecycle, I not only equip myself with the technical knowledge needed to excel in interviews but also prepare to tackle real-world challenges head-on. This journey transforms me into a more confident developer, ready to showcase my expertise and adaptability in a fast-paced environment like Meta.

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