Express Framework Interview Questions

Checkout Vskills Interview questions with answers in Express Framework  to prepare for your next job role. The questions are submitted by professionals to help you to prepare for the Interview.

Q.1 What is Express.js, and how does it differ from Node.js?

Express.js is a web application framework built on top of Node.js. It simplifies the process of building web applications by providing a set of features and utilities. Node.js, on the other hand, is a runtime environment for executing JavaScript on the server side.

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Q.2 Explain the role of middleware in Express.js.

Middleware functions in Express.js have access to the request, response, and the next middleware function in the application's request-response cycle. They can perform tasks such as modifying the request or response objects, terminating the request-response cycle, or calling the next middleware in the stack.

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Q.3 How do you handle routing in Express.js?

Express.js provides a simple and expressive way to define routes using the app.get(), app.post(), etc. methods. Routes are defined by specifying a path and a callback function that gets executed when the route is matched.

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Q.4 What is the purpose of the app.use() function in Express.js?

app.use() is used to mount middleware functions in the Express.js application. It can be used to define middleware that is executed for every request to the server.

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Q.5 Explain the significance of the next() function in middleware.

The next() function is used in middleware to pass control to the next middleware function in the stack. If next() is not called, the request-response cycle is terminated, and no further middleware in the stack will be executed.

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Q.6 How does Express.js handle error handling in middleware?

Express.js has a special middleware for error handling. Middleware with four parameters (err, req, res, next) is treated as error-handling middleware. When an error occurs, Express.js will skip regular middleware and call error-handling middleware.

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Q.7 What is the purpose of the app.listen() method in Express.js?

The app.listen() method is used to bind and listen for connections on the specified host and port. It starts the Express.js application and makes it available for incoming requests.

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Q.8 Explain the concept of route parameters in Express.js.

Route parameters are named segments of the URL path that capture the values specified at their position. They are defined by placing a colon (:) followed by the parameter name in the route's path.

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Q.9 How does Express.js handle static files?

Express.js uses the express.static middleware to serve static files, such as images, CSS, and JavaScript. You can specify a directory to serve static files using express.static('public'), where 'public' is the directory name.

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Q.10 What is the purpose of the req.params object in Express.js?

The req.params object in Express.js contains properties mapped to the named route parameters. It allows access to the values of route parameters in the callback function handling the request.

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Q.11 Explain the use of template engines in Express.js.

Template engines in Express.js allow dynamic generation of HTML by embedding variables and logic into the HTML. Popular template engines for Express include EJS, Pug (formerly Jade), and Handlebars.

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Q.12 How can you set up middleware to handle CORS in Express.js?

You can use the cors middleware to handle Cross-Origin Resource Sharing (CORS) in Express.js. It simplifies the process of configuring CORS headers and handling various CORS-related scenarios.

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Q.13 What is the purpose of the res.json() method in Express.js?

res.json() sends a JSON response from the server. It automatically sets the Content-Type header to application/json and converts the JavaScript object passed to it into a JSON string.

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Q.14 How does Express.js support sessions and cookies?

Express.js provides middleware like express-session to handle sessions and cookie-parser for parsing cookies. Sessions allow storing user data between requests, and cookies are used to store small pieces of data on the client's side.

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Q.15 What is the role of the body-parser middleware in Express.js?

The body-parser middleware parses the incoming request body and makes it available under the req.body property. It is commonly used for handling form submissions and JSON payloads.

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Q.16 Explain the difference between app.all() and app.all('*', ...) in Express.js.

app.all() matches all HTTP methods for the specified route, while app.all('*') matches all routes for all HTTP methods. The latter is often used to create a catch-all route for unmatched paths.

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Q.17 How can you secure an Express.js application?

Securing an Express.js application involves using best practices such as validating user inputs, employing middleware for security headers, implementing authentication and authorization, and keeping dependencies up to date.

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Q.18 What is the purpose of the express.Router() in Express.js?

express.Router() allows creating modular, mountable route handlers in Express.js applications. It is useful for organizing routes into separate files or components.

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Q.19 Explain the role of the app.locals object in Express.js.

The app.locals object in Express.js is an object that exposes variables to the application locals. Its properties are available in all templates rendered within the application.

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Q.20 How can you handle file uploads in Express.js?

File uploads in Express.js can be handled using middleware like multer. It allows handling multipart/form-data, making it easy to process files uploaded through HTML forms.

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Q.21 What is Express.js, and how does it facilitate web development with Node.js?

Express.js is a web application framework for Node.js. It simplifies the process of building robust and scalable web applications by providing a set of features and middleware.

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Q.22 Explain the concept of middleware in Express.js.

Middleware functions in Express.js are functions that have access to the request, response, and next middleware function in the application’s request-response cycle. They can modify the request and response objects, end the request-response cycle, or call the next middleware in the stack.

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Q.23 How does routing work in Express.js?

Express.js uses a routing mechanism to define how an application responds to client requests. It allows developers to define routes based on HTTP methods and URL patterns.

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Q.24 What is the purpose of route parameters in Express.js?

Route parameters in Express.js are named segments in the URL path that capture values. They are specified in the route definition with a colon (:) followed by the parameter name.

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Q.25 How can you handle errors in Express.js middleware?

Error handling middleware in Express.js has four parameters (err, req, res, next). When an error occurs, it skips regular middleware and executes the error-handling middleware.

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Q.26 What is the role of the app.listen() method in Express.js?

The app.listen() method binds the Express.js application to a specified host and port, allowing it to listen for incoming connections and handle HTTP requests.

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Q.27 Explain how template engines are used in Express.js.

Template engines in Express.js allow dynamic generation of HTML. Examples include EJS, Pug, and Handlebars. They facilitate embedding variables and logic within HTML templates.

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Q.28 How does Express.js handle sessions and cookies?

Express.js has middleware like express-session for handling sessions and cookie-parser for parsing cookies. Sessions store user data between requests, while cookies store small pieces of data on the client side.

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Q.29 What is the purpose of the body-parser middleware in Express.js?

The body-parser middleware parses the incoming request body, making it accessible under req.body. It is commonly used for handling form submissions and JSON payloads.

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Q.30 Explain the concept of route grouping in Express.js.

Route grouping in Express.js allows developers to organize routes under a common path prefix. It is useful for modularizing and structuring the application's route handling.

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Q.31 How can you implement CORS handling in an Express.js application?

CORS (Cross-Origin Resource Sharing) can be handled in Express.js using the cors middleware. It simplifies configuring headers to allow or restrict cross-origin requests.

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Q.32 Explain the difference between app.all() and app.all('*') in Express.js.

app.all() matches all HTTP methods for a specified route, while app.all('*') matches all routes for all HTTP methods. The latter is often used as a catch-all route for unmatched paths.

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Q.33 What is Express.js, and why is it used in Node.js development?

Express.js is a web application framework for Node.js that simplifies the creation of robust and scalable web applications. It provides a set of features and middleware to streamline development.

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Q.34 How does Express.js handle routing?

Express.js uses a routing mechanism to define how an application responds to client requests. Developers can define routes based on HTTP methods and URL patterns.

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Q.35 What is Express.js?

Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

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Q.36 Explain Middleware in Express.

Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application's request-response cycle.

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Q.37 Differentiate between app.get() and app.use() in Express.

app.get() is used for defining routes for specific HTTP GET requests, while app.use() is used for including middleware functions that execute during the request-response cycle.

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Q.38 What is the significance of app.listen() in Express?

app.listen() starts a server to listen on a specified port and a callback function is executed once the server starts listening.

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Q.39 How does error handling work in Express?

Error handling in Express involves using middleware functions with four parameters (err, req, res, next) to catch errors during the request-response cycle.

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Q.40 Explain the purpose of req.params in Express.

req.params is an object containing properties mapped to the named route parameters.

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Q.41 What are route handlers in Express?

Route handlers are functions that handle requests to specific routes, defined using HTTP methods like GET, POST, PUT, DELETE, etc.

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Q.42 How does Express handle static files?

Express serves static files such as images, CSS, and JavaScript files using the express.static() middleware function.

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Q.43 What is the role of app.use(bodyParser.json()) in Express?

It parses incoming request bodies in JSON format and is commonly used to handle JSON-formatted data sent by clients.

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Q.44 Explain the purpose of the Express Router.

The Express Router allows for creating modular, mountable route handlers to effectively handle specific routes or groups of routes in an application.

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Q.45 How can you handle CORS in Express?

CORS (Cross-Origin Resource Sharing) can be handled in Express using middleware such as cors to enable or restrict access to resources from different origins.

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Q.46 Discuss the use of template engines in Express.

Template engines like EJS, Pug, or Handlebars are used in Express to generate dynamic HTML content by combining data with predefined templates.

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Q.47 What is the role of next() in Express middleware?

next() is a function used to pass control to the next middleware function in the stack. It is often used to trigger the next middleware in the chain.

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Q.48 Explain the difference between res.send() and res.json() in Express.

res.send() can send various HTTP responses, while res.json() specifically sends a JSON response.

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Q.49 How do you handle authentication and authorization in Express?

Authentication verifies the user's identity, while authorization determines the user's access rights. Strategies like JWT, OAuth, or Passport.js are commonly used for this purpose in Express.

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Q.50 Discuss the use of environment variables in Express applications.

Environment variables are used to configure and manage sensitive or environment-specific data in Express applications, enhancing security and flexibility.

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Q.51 What is the purpose of the app.locals object in Express?

app.locals provides access to variables that are available in the application's local scope and can be used across all views rendered during a request-response cycle.

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Q.52 How can you handle file uploads in Express?

File uploads can be handled in Express using middleware such as multer, which facilitates handling multipart/form-data.

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Q.53 Explain the concept of sessions in Express.

Sessions in Express are used to store user-specific data across multiple requests and are often managed using middleware like express-session.

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Q.54 What is the purpose of the app.all() method in Express?

app.all() is used to handle all HTTP methods for a specific route and is often used for creating global middleware.

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Q.55 Discuss the role of the app.set() method in Express.

app.set() is used to assign values to application settings that are used throughout the application.

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Q.56 How can you implement logging in an Express application?

Logging in Express can be implemented using middleware like morgan to log HTTP requests and other application-related information.

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Q.57 Explain the concept of clustering in Express.

Clustering in Express involves creating multiple instances (workers) of the application to take advantage of multi-core systems for improved performance and scalability.

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Q.58 Discuss the role of error-first callbacks in Express.

Error-first callbacks are a convention in Node.js where the first parameter of a callback function is reserved for an error object.

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Q.59 How do you handle HTTPS/SSL in Express?

HTTPS/SSL can be implemented in Express by creating an HTTPS server using the https module and providing the necessary SSL certificates.

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Q.60 What are some best practices for optimizing Express applications?

Best practices include using middleware effectively, implementing caching, optimizing database queries, securing dependencies, using environment-specific configurations, and employing gzip compression for response payloads.

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