Interview Questions and Answers

Middleware functions are functions that have access to the request, response, and the next function in the application’s request-response cycle.

Routing refers to how an application’s endpoints (URIs) respond to client requests. In Express, you can define routes to handle different HTTP methods and URL patterns.

app.use() is used to mount middleware functions in the application. It is executed every time a request is received.

res.send() sends a response of various types, while res.json() specifically sends a JSON response.

Express Router is a middleware that can be used to define modular routes for your application.

You can handle errors in Express.js using middleware with four parameters (err, req, res, next) or using try-catch blocks.

body-parser is used to parse the incoming request bodies in a middleware before the handlers, making it easier to handle form data and JSON payloads.

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

PUT is used to update or create a resource entirely, while PATCH is used to apply partial modifications to a resource.

You can define a route parameter by using a colon (:) followed by the parameter name in the route definition. For example, '/users/:id'.

Middleware chaining is the process of calling multiple middleware functions in sequence for a specific route or globally using 'app.use()'.

The 'static' middleware is used to serve static files, such as images, CSS, and JavaScript files, from a specified directory.

You can handle CORS by using the 'cors' middleware or by manually setting the appropriate headers in the response.

The 'express.Router' class is used to create modular, mountable route handlers. It can be thought of as a mini Express application.

'cookie-parser' is a middleware used to parse cookie headers and populate 'req.cookies' with an object keyed by the cookie names.

'helmet' is a middleware that helps secure Express.js applications by setting various HTTP headers to prevent common web vulnerabilities.

'express.json()' is a middleware that parses incoming JSON requests, populating the 'req.body' property with the parsed data.

'express.static()' is a middleware that serves static files, such as images, CSS, and JavaScript files, from a specified directory.

You can handle query parameters in Express.js using the 'req.query' object, which contains key-value pairs of the query parameters.

'express.urlencoded()' is a middleware that parses incoming requests with URL-encoded payloads and is based on the 'body-parser' library.