1
ExpressJS: Express is a flexible Node.js web application framework that provides a wide set of features to develop web and mobile applications.
2
Mongoose: Mongoose is also a Node.js web application framework that makes it easy to connect an application to a database.
3
JWT: json web tokens for authentication and authorisation
4
Puppeteer: For web scraping and crawling.

Difficulty: 4/10

Topics: HTTP frameworks, ORM/DB libraries, testing utilities

0-2 years experience

1
We're building a simple CLI tool in Node.js that needs to parse command‑line arguments. Which library would you reach for, and how would you use it?
2
If you need to make an HTTP request to an external API in a small script, which library would you choose and why?
3
You need to write unit tests for a tiny module. Which testing library would you pick and how would you set it up?

2-5 years experience

1
Our service uses Express for routing, but request bodies aren't being parsed correctly for JSON payloads. How would you troubleshoot and which middleware would you add?
2
We want to move from callbacks to promises for database access. Which ORM or query library would you recommend, and what migration steps would you take?
3
During a feature rollout we need input validation. Which validation library would you integrate with Express, and what trade‑offs does it have versus custom validators?

5-8 years experience

1
Our microservice ecosystem uses both Express and Fastify in different services. How would you decide which framework to standardize on, considering performance, ecosystem, and team expertise?
2
A monolithic app uses Mongoose for MongoDB but we need better query performance and type safety. How would you evaluate alternative ORMs or query builders, and what migration plan would you propose?
3
The team wants a testing strategy that covers unit, integration, and end‑to‑end tests. How would you choose a combination of libraries (e.g., Jest, Mocha, Supertest) to meet those needs while keeping CI fast?

8+ years experience

1
Our company has dozens of services each using different logging and monitoring libraries. How would you design a unified logging strategy, pick a core library, and plan a migration that minimizes runtime overhead?
2
We’re planning a major Node.js version upgrade across all services and need to audit third‑party dependencies for compatibility. How would you create a process to evaluate critical libraries like Express, Sequelize, and Jest for future‑proofing and security?
3
Given the need to support both server‑side rendering and API endpoints, how would you architect the project structure and library choices (frameworks, templating, data layer) to maximize reuse and maintainability across multiple teams?

❓What steps would you take to add that library to an existing project?
❓How do you keep the library up to date without breaking production?
❓Can you give an example of a situation where you’d choose a less‑common alternative?