Question 1

What is the difference between 'require' and 'import' in Node.js?

Accepted Answer

require() is Node.js’s CommonJS module system, while import is part of ES Modules (ESM), introduced later.
- require is synchronous and widely used in older code.
- import is async, supports tree-shaking, and needs 'type': 'module' in package.json.
- ESM is the modern standard, but both coexist.

Question 2

How do you implement rate limiting in a Node.js application?

Accepted Answer

Rate limiting restricts the number of requests a client can make, preventing abuse. In Node.js with Express, you can use the 'express-rate-limit' package.
- Set limits like 100 requests per hour per IP.
- Helps protect APIs from DDoS attacks.
- Configurable with custom messages or windows.

Question 3

How do you implement pagination in a Node.js API?

Accepted Answer

Pagination splits large datasets into smaller chunks.
- Use query params like ?page=1&limit=10.
- Calculate offset and fetch from database (e.g., SQL LIMIT).
- Return metadata (total, pages) with results.
- Improves performance and UX.

Question 4

How do you handle file uploads in a Node.js application?

Accepted Answer

File uploads in Node.js with Express can use middleware like 'multer'.
- Multer parses multipart/form-data, saving files to disk or memory.
- Validate file types and sizes for security.
- Streams can handle large files efficiently.
- Respond with success or error messages.

Question 5

What is middleware in the context of Express.js?

Accepted Answer

Middleware in Express.js are functions that process requests before they reach route handlers. They can modify requests, responses, or terminate the request-response cycle.
- Common uses: logging, authentication, parsing.
- Applied globally with app.use() or per route.
- Next() passes control to the next middleware.

Question 6

What is callback hell and how do you avoid it?

Accepted Answer

Callback hell is the nesting of multiple callbacks, making code hard to read and maintain.
- Avoid it with Promises or async/await for cleaner flow.
- Modularize code into smaller functions.
- Improves debugging and scalability.

Question 7

What is the difference between 'npm install' and 'npm ci'?

Accepted Answer

Both install dependencies, but they serve different purposes.
- 'npm install' updates package.json and installs based on it.
- 'npm ci' uses package-lock.json for a clean, reproducible build.
- ci is faster and stricter, ideal for CI/CD.
- install is more flexible for dev.

Question 8

What is the difference between 'development' and 'production' modes in Node.js?

Accepted Answer

In Node.js, modes are set via NODE_ENV.
- Development: Enables verbose logging, no minification, and debugging.
- Production: Optimizes for speed, security, and minimal logs.
- Use environment variables to toggle behavior.
- Impacts performance and error handling.

Question 9

How do you handle cross-site scripting (XSS) in a Node.js app?

Accepted Answer

XSS occurs when malicious scripts are injected into web pages.
- Sanitize user input with libraries like 'sanitize-html'.
- Use Helmet to set Content-Security-Policy headers.
- Escape output in templates (e.g., EJS).
- Prevents client-side attacks.

Question 10

How do you implement authentication in a Node.js app?

Accepted Answer

Authentication in Node.js can use JWT, OAuth, or Passport.js.
- JWT: Issue tokens after login, verify on protected routes.
- Store passwords securely with bcrypt.
- Use middleware to check auth status.
- Sessions or cookies are alternatives for stateful auth.

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