15 React Router Interview Questions and Answers

React Router is an essential library for any developer working with React applications. It enables dynamic routing, allowing for seamless navigation and rendering of components based on the URL. This functionality is crucial for creating single-page applications (SPAs) that provide a smooth user experience without the need for full page reloads. React Router’s flexibility and ease of integration make it a go-to solution for managing routes in modern web development.

This article offers a curated selection of interview questions focused on React Router. By familiarizing yourself with these questions and their answers, you’ll be better prepared to demonstrate your expertise in routing and navigation within React applications, showcasing your ability to build efficient and user-friendly web interfaces.

React Router Interview Questions and Answers

1. How do you create a simple route that renders a component when the URL matches /home?

To create a simple route in React Router that renders a component when the URL matches /home, set up the Router and define the Route. React Router is a library for routing in React, enabling navigation among views, changing the browser URL, and keeping the UI in sync with the URL.

Example:

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

const Home = () => <h1>Home Component</h1>;

const App = () => (
  <Router>
    <Switch>
      <Route exact path="/home" component={Home} />
    </Switch>
  </Router>
);

export default App;

In this example, the Home component is rendered when the URL matches /home. The Router wraps the application, and the Switch groups the Route components. The Route specifies the path and the component to render.

2. Write a route configuration that includes nested routes for a blog application with paths /blog, /blog/:id, and /blog/:id/comments.

Nested routes in React Router allow you to define routes within other routes, creating a hierarchical structure. This is useful for applications with complex navigation, such as a blog with paths like /blog, /blog/:id, and /blog/:id/comments.

Example:

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import Blog from './Blog';
import BlogPost from './BlogPost';
import Comments from './Comments';

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/blog" component={Blog} />
        <Route exact path="/blog/:id" component={BlogPost} />
        <Route path="/blog/:id/comments" component={Comments} />
      </Switch>
    </Router>
  );
}

export default App;

In this configuration:

• The /blog path renders the Blog component, displaying a list of blog posts.
• The /blog/:id path renders the BlogPost component, displaying a specific post based on the id parameter.
• The /blog/:id/comments path renders the Comments component, displaying comments for the specific post.

3. How can you pass props to a component rendered by a Route? Provide an example.

In React Router, you can pass props to a component rendered by a Route using the render method instead of the component method. The render method allows you to pass props directly to the component.

Example:

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

const ExampleComponent = ({ message }) => {
  return <div>{message}</div>;
};

const App = () => {
  const message = "Hello, World!";
  
  return (
    <Router>
      <Route 
        path="/example" 
        render={(props) => <ExampleComponent {...props} message={message} />} 
      />
    </Router>
  );
};

export default App;

4. How do you handle 404 errors in a React Router application?

Handling 404 errors in a React Router application involves setting up a catch-all route that matches any path not explicitly defined. This is typically done using a wildcard route that renders a 404 component when no other routes match.

Example:

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import Home from './Home';
import About from './About';
import NotFound from './NotFound';

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/" component={Home} />
        <Route path="/about" component={About} />
        <Route component={NotFound} />
      </Switch>
    </Router>
  );
}

export default App;

In this example, the Switch component renders the first route that matches the current location. If none match, the NotFound component is rendered, handling 404 errors.

5. Write a route configuration that uses Redirect to navigate from /old-path to /new-path.

In React Router, the Redirect component is used to navigate from one route to another. This is useful for handling deprecated routes or redirecting users to a new path. The Redirect component can be used within a Route component to specify the old path and the new path.

Example:

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

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/old-path">
          <Redirect to="/new-path" />
        </Route>
        <Route path="/new-path">
          <NewPathComponent />
        </Route>
        {/* Other routes */}
      </Switch>
    </Router>
  );
}

function NewPathComponent() {
  return <div>Welcome to the new path!</div>;
}

6. Explain the use of the useParams hook and provide an example of its usage.

The useParams hook in React Router allows you to access the parameters of the current route. This is useful for routes with dynamic segments, such as user IDs or product IDs. By using useParams, you can easily extract these parameters and use them within your component.

Example:

import React from 'react';
import { useParams } from 'react-router-dom';

const UserProfile = () => {
    const { userId } = useParams();

    return (
        <div>
            <h1>User Profile</h1>
            <p>User ID: {userId}</p>
        </div>
    );
};

export default UserProfile;

In this example, the UserProfile component uses the useParams hook to extract the userId parameter from the URL, allowing the component to display the user ID dynamically.

7. How can you programmatically navigate to a different route within a component?

In React Router, programmatic navigation allows you to navigate to different routes within a component without using <Link> or <NavLink>. This is useful for navigation based on certain conditions or events, such as form submissions or button clicks.

For React Router v5, use the useHistory hook:

import { useHistory } from 'react-router-dom';

function MyComponent() {
    const history = useHistory();

    const handleClick = () => {
        history.push('/new-route');
    };

    return (
        <button onClick={handleClick}>Go to New Route</button>
    );
}

For React Router v6, use the useNavigate hook:

import { useNavigate } from 'react-router-dom';

function MyComponent() {
    const navigate = useNavigate();

    const handleClick = () => {
        navigate('/new-route');
    };

    return (
        <button onClick={handleClick}>Go to New Route</button>
    );
}

8. Write a custom hook that logs the current pathname whenever it changes.

In React, custom hooks allow you to extract and reuse stateful logic across multiple components. React Router provides hooks like useLocation to access the current location object, which includes the pathname. By combining these, we can create a custom hook that logs the current pathname whenever it changes.

import { useEffect } from 'react';
import { useLocation } from 'react-router-dom';

function useLogPathname() {
    const location = useLocation();

    useEffect(() => {
        console.log(location.pathname);
    }, [location.pathname]);
}

export default useLogPathname;

9. How would you implement lazy loading of routes in a React application? Provide an example.

Lazy loading in a React application can be achieved using the React.lazy function and Suspense component. This allows you to load components only when they are needed, reducing the initial load time. React Router can be integrated with these features to lazy load routes.

Example:

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

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

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

export default App;

In this example, the Home and About components are loaded only when their respective routes are accessed. The Suspense component provides a fallback UI while the components are being loaded.

10. Explain the concept of dynamic routing and provide an example where it might be useful.

Dynamic routing in React Router enables the creation of routes determined at runtime, based on the application’s state or data. This is useful in scenarios where the routes depend on user input or data fetched from an API.

For instance, consider a blog application where each post has a unique ID. Instead of defining a route for each post manually, dynamic routing allows you to create a single route that can handle any post ID.

Example:

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

const BlogPost = ({ match }) => {
    const { id } = match.params;
    // Fetch blog post data using the id
    return <div>Blog Post ID: {id}</div>;
};

const App = () => (
    <Router>
        <Switch>
            <Route path="/post/:id" component={BlogPost} />
        </Switch>
    </Router>
);

export default App;

In this example, the :id parameter in the route path allows the BlogPost component to access the ID of the blog post from the URL, enabling the application to dynamically render different posts.

11. How can you animate transitions between routes? Provide a brief example.

Animating transitions between routes in React Router can be achieved using libraries like react-transition-group. This library provides components that help manage the transition states of elements, making it easier to animate route changes.

To animate transitions between routes, wrap your routes with the CSSTransition component from react-transition-group. This component allows you to define the animation classes and durations for entering and exiting elements.

Example:

import React from 'react';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';
import { CSSTransition, TransitionGroup } from 'react-transition-group';
import Home from './Home';
import About from './About';
import './styles.css';

const App = () => (
  <Router>
    <Route render={({ location }) => (
      <TransitionGroup>
        <CSSTransition
          key={location.key}
          timeout={300}
          classNames="fade"
        >
          <Switch location={location}>
            <Route exact path="/" component={Home} />
            <Route path="/about" component={About} />
          </Switch>
        </CSSTransition>
      </TransitionGroup>
    )} />
  </Router>
);

export default App;

In the above example, the CSSTransition component wraps the Switch component, which contains the routes. The classNames prop specifies the base name for the CSS classes applied during the transition, and the timeout prop defines the duration.

12. Describe how you would handle query parameters in a route. Provide an example.

To handle query parameters in a route using React Router, you can utilize the useLocation hook to access the current location object, which includes the search string containing the query parameters. Additionally, the useHistory hook can be used to programmatically navigate and update the query parameters.

Example:

import React from 'react';
import { useLocation, useHistory } from 'react-router-dom';

const QueryParamsExample = () => {
  const location = useLocation();
  const history = useHistory();

  const queryParams = new URLSearchParams(location.search);
  const paramValue = queryParams.get('paramName');

  const updateQueryParams = () => {
    queryParams.set('paramName', 'newValue');
    history.push({ search: queryParams.toString() });
  };

  return (
    <div>
      <p>Current Param Value: {paramValue}</p>
      <button onClick={updateQueryParams}>Update Query Param</button>
    </div>
  );
};

export default QueryParamsExample;

In this example, useLocation is used to access the current URL’s query parameters, and useHistory is used to update them. The URLSearchParams interface provides methods to work with the query string of a URL.

13. Write a route configuration that supports both static and dynamic segments, such as /products and /products/:id.

In React Router, route configuration allows you to define the paths your application will respond to. Static segments are fixed paths, while dynamic segments can change based on the parameters passed. React Router uses the colon (:) syntax to denote dynamic segments.

Example:

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

function App() {
  return (
    <Router>
      <Switch>
        <Route exact path="/products" component={Products} />
        <Route path="/products/:id" component={ProductDetail} />
      </Switch>
    </Router>
  );
}

export default App;

In this example, the /products route is a static segment that will render the Products component. The /products/:id route is a dynamic segment that will render the ProductDetail component based on the id parameter.

14. How do you create custom route components and why would you use them? Provide an example.

Custom route components in React Router are used to encapsulate route-specific logic and UI, making the codebase more modular and maintainable. They allow you to define routes with additional functionality, such as authentication checks, layout wrappers, or any other custom logic that needs to be applied to specific routes.

Example:

import React from 'react';
import { Route, Redirect } from 'react-router-dom';

// Custom route component for protected routes
const ProtectedRoute = ({ component: Component, isAuthenticated, ...rest }) => (
  <Route
    {...rest}
    render={props =>
      isAuthenticated ? (
        <Component {...props} />
      ) : (
        <Redirect to="/login" />
      )
    }
  />
);

export default ProtectedRoute;

Usage:

import React from 'react';
import { BrowserRouter as Router, Switch } from 'react-router-dom';
import ProtectedRoute from './ProtectedRoute';
import HomePage from './HomePage';
import LoginPage from './LoginPage';

const App = () => {
  const isAuthenticated = true; // This should come from your authentication logic

  return (
    <Router>
      <Switch>
        <ProtectedRoute path="/home" component={HomePage} isAuthenticated={isAuthenticated} />
        <Route path="/login" component={LoginPage} />
      </Switch>
    </Router>
  );
};

export default App;

15. Explain how to handle nested routes and provide an example.

In React Router, nested routes allow you to render child components within a parent component, creating a hierarchical structure of routes. This is useful for building complex user interfaces where different parts of the UI need to be rendered based on the URL.

To handle nested routes, define a parent route and specify child routes within the parent component. The child routes will be rendered inside the parent component using the <Outlet /> component provided by React Router.

Example:

import { BrowserRouter as Router, Routes, Route, Link, Outlet } from 'react-router-dom';

function App() {
  return (
    <Router>
      <nav>
        <Link to="/dashboard">Dashboard</Link>
      </nav>
      <Routes>
        <Route path="/dashboard" element={<Dashboard />}>
          <Route path="stats" element={<Stats />} />
          <Route path="settings" element={<Settings />} />
        </Route>
      </Routes>
    </Router>
  );
}

function Dashboard() {
  return (
    <div>
      <h2>Dashboard</h2>
      <nav>
        <Link to="stats">Stats</Link>
        <Link to="settings">Settings</Link>
      </nav>
      <Outlet />
    </div>
  );
}

function Stats() {
  return <h3>Stats</h3>;
}

function Settings() {
  return <h3>Settings</h3>;
}

In this example, the Dashboard component serves as the parent route, and it contains links to the Stats and Settings child routes. The <Outlet /> component is used to render the child routes within the Dashboard component.