Express Middleware Quiz

To pass the quiz, you must correctly answer at least 18 of the 20 questions below. # --quizzes-- ## --quiz-- ### --question-- #### --text-- What is middleware in Express? #### --distractors-- A function that starts the Express server and binds it to a port. --- A configuration object that defines routes and their handlers. --- A built-in database connector for handling persistent data. #### --answer-- A function that executes during the lifecycle of a request to the server. ### --question-- #### --text-- What three things does a middleware function have access to? #### --distractors-- The database connection, the session store, and the route definition. --- The server config, the port number, and the app instance. --- The environment variables, the request headers, and the response status. #### --answer-- The request object (`req`), the response object (`res`), and the `next` function. ### --question-- #### --text-- What happens if a middleware function does not call `next()`? #### --distractors-- Control is passed automatically to the next middleware in the stack. --- Express throws an unhandled error and crashes the server. --- The request is retried from the beginning of the middleware stack. #### --answer-- The request-response cycle stops. ### --question-- #### --text-- What does `app.use()` do? #### --distractors-- Defines a `GET` route handler for a specific path. --- Starts the server and begins listening for incoming connections. --- Creates a new instance of the Express application. #### --answer-- Adds middleware globally to the application. ### --question-- #### --text-- In what order is middleware executed in an Express app? #### --distractors-- In reverse order, starting from the last middleware added. --- Alphabetically, based on the middleware function names. --- Randomly, depending on which request arrives first. #### --answer-- In the order it is added to the app. ### --question-- #### --text-- What is application-level middleware bound to? #### --distractors-- A specific route instance created with `express.Router()`. --- The Node.js HTTP server returned by `app.listen()`. --- An individual route handler defined with `app.get()` or `app.post()`. #### --answer-- An instance of the Express app. ### --question-- #### --text-- Which of the following can be used to register application-level middleware? #### --distractors-- `app.listen()` or route-specific methods like `app.get()` and `app.delete()` --- `app.route()` or route-specific methods like `app.patch()` and `app.options()` --- `router.use()` or route-specific methods like `router.get()` and `router.post()` #### --answer-- `app.use()` or route-specific methods like `app.get()` and `app.post()` ### --question-- #### --text-- What is router-level middleware bound to? #### --distractors-- The main Express app instance created with `express()`. --- The Node.js `http` module's server object. --- A specific route handler callback function. #### --answer-- An instance of `express.Router()`. ### --question-- #### --text-- Which method is used to apply router-level middleware? #### --distractors-- `app.use()` --- `express.use()` --- `app.router()` #### --answer-- `router.use()` ### --question-- #### --text-- How do you scope router-level middleware to a specific path in your app? #### --distractors-- By calling `router.scope('/path')` before defining routes. --- By passing the path directly to `router.use()` in the main file. --- By setting `router.basePath = '/path'` before mounting it. #### --answer-- By mounting the router with `app.use('/path', router)`. ### --question-- #### --text-- What makes error-handling middleware different from regular middleware in Express? #### --distractors-- It uses `res.error()` instead of `res.send()` to respond to the client, bypassing the normal response flow. --- It must be defined before all other routes so it can intercept errors before they reach any route handler. --- It is registered with `app.error()` instead of `app.use()`, which signals to Express it should handle errors. #### --answer-- It has four parameters (`err`, `req`, `res`, and `next`), and the `err` parameter tells Express it is an error handler. ### --question-- #### --text-- When is error-handling middleware invoked? #### --distractors-- When a route handler returns a response with a 4xx or 5xx status code. --- When the server receives more than one request at the same time. --- When the request takes longer than the default timeout to complete. #### --answer-- When an error is passed to `next(err)`. ### --question-- #### --text-- Where must error-handling middleware be placed in the middleware stack? #### --distractors-- At the top, before any routes are defined. --- Immediately after the route that is most likely to throw an error. --- At the same level as other middleware, in any position. #### --answer-- At the end, after all other middleware and routes. ### --question-- #### --text-- What does the built-in `express.json()` middleware do? #### --distractors-- Serves JSON files stored in the public directory to the client. --- Converts the response object to JSON before sending it to the client. --- Validates that all incoming requests contain a valid JSON content-type header. #### --answer-- Parses incoming requests with JSON payloads. ### --question-- #### --text-- What does `express.static()` do? #### --distractors-- Parses incoming requests with URL-encoded form data. --- Caches route handler responses to improve performance. --- Registers static route paths that cannot be changed at runtime. #### --answer-- Serves static files such as images, CSS, and JavaScript. ### --question-- #### --text-- What does `express.urlencoded()` parse, and where is the result available? #### --distractors-- It parses JSON payloads and makes the result available on `req.json`. --- It parses query strings from the URL and makes them available on `req.query`. --- It parses multipart form data and makes the files available on `req.files`. #### --answer-- It parses URL-encoded payloads from HTML forms and makes the data available on `req.body`. ### --question-- #### --text-- What does the third-party `cors` middleware do? #### --distractors-- Logs all incoming HTTP requests with method, URL, and response time. --- Parses cookies from incoming requests and attaches them to `req.cookies`. --- Compresses response bodies to reduce the size of data sent to the client. #### --answer-- Enables Cross-Origin Resource Sharing. ### --question-- #### --text-- Which of the following correctly classifies Express middleware? #### --distractors-- `morgan` is built-in while `express.static()` is third-party --- `cors` is built-in while `morgan` is third-party --- `express.urlencoded()` is built-in while `express.json()` is third-party #### --answer-- `express.json()` is built-in while `cors` is third-party ### --question-- #### --text-- What does the third-party middleware `morgan` do? #### --distractors-- Enables Cross-Origin Resource Sharing. --- Parses cookies from incoming requests and attaches them to `req.cookies`. --- Compresses response bodies to reduce the size of data sent to the client. #### --answer-- Logs HTTP requests. ### --question-- #### --text-- What happens when a middleware function calls `next()`? #### --distractors-- The request is immediately sent back to the client with a 200 status. --- The current middleware function restarts from the beginning. --- Express skips all remaining middleware and executes the final route handler. #### --answer-- Control passes to the next middleware or route handler in the stack.