Express.js Interview Questions and Answers

Answer: Both b and c

Clustering spawns multiple worker processes to utilize all CPU cores. Each worker runs a separate Node.js instance. Improves performance and reliability.

Answer: A minimal and flexible Node.js web application framework

Express.js is a fast, unopinionated, minimalist web framework for Node.js. It provides a robust set of features for building web and mobile applications.

Answer: Both b and c

Express Router is a complete middleware and routing system. It allows you to create modular, mountable route handlers in separate files.

Answer: npm install express

Express is installed using npm (Node Package Manager) with the command `npm install express`. You can also use yarn: `yarn add express`.

Answer: express.Router()

Create a router using `const router = express.Router()`. Then define routes on router and export it to be used with app.use().

Answer: All of the above

Use built-in cluster module. Master process forks workers equal to CPU cores. Incoming connections distributed across workers using round-robin.

Answer: All of the above

Route middleware runs only for specific routes. Pass middleware as arguments before the handler: `app.get('/path', middleware1, middleware2, handler)`

Answer: require('express')()

Create an Express app by requiring the module and calling it as a function: `const express = require('express'); const app = express();`

Answer: Both b and c

PM2 is a production process manager. Features: cluster mode, auto-restart on crash, log management, monitoring, zero-downtime deployments.

Answer: All of the above

Error-handling middleware has four parameters. Define it after all other middleware. It catches errors passed to next(err) or thrown in async code.

Answer: app.listen()

The `app.listen(port, callback)` method binds and listens for connections on the specified port. Example: `app.listen(3000, () => console.log('Server running'))`

Answer: All of the above

Graceful shutdown completes in-flight requests before stopping. Listen for SIGTERM/SIGINT signals, close server, close DB connections, then exit.

Answer: All of the above

Streaming processes data in chunks without loading entire content in memory. Essential for large files. Use Node.js streams with pipe() method.

Answer: A URL path that maps to a handler function

A route determines how an application responds to a client request at a specific endpoint (URI) and HTTP method. Example: `app.get('/users', handler)`

Answer: next(error)

Pass errors by calling `next(error)`. For synchronous code, you can throw, but it must be caught. For async code, always use next(error).

Answer: GET

GET method is used to retrieve data from the server. It should not modify server state and is idempotent (same result for multiple identical requests).

Answer: Both b and c

Template engines generate HTML dynamically by combining templates with data. Popular choices: EJS, Pug (formerly Jade), Handlebars, Mustache.

Answer: All of the above

Caching stores frequently accessed data to reduce database load and improve response time. Use Redis, Memcached, or in-memory caches like node-cache.

Answer: All of the above

Use Redis client library. Create cache middleware that checks Redis before executing handler. Set appropriate TTL (Time To Live) for cached data.

Answer: app.get(path, handler)

Define a GET route using `app.get(path, handler)`. Example: `app.get('/users', (req, res) => { res.send('Users list'); })`

Answer: app.set('view engine', 'ejs')

Set template engine using `app.set('view engine', 'engineName')`. Also set views directory: `app.set('views', './views')`

Answer: All of the above

Connection pooling maintains a pool of reusable database connections. Reduces overhead of creating/destroying connections. Configure pool size based on load.

Answer: Both a and b

Route handlers receive request (req) and response (res) objects. req contains request data, res is used to send the response back to the client.

Answer: res.render(view, data)

`res.render(view, data)` renders a view template with data and sends the resulting HTML to the client. View file extension can be omitted.