Node.js & Express: Runtime and API Design

Explain how Node.js's event-driven, non-blocking I/O model enables high concurrency and how it differs from traditional multi-threaded models.

Describe the differences between the CommonJS and ES Module systems in Node.js, including syntax and loading behavior.

Explain the middleware pattern in Express and how the 'next()' function passes control through the request-response cycle.

Compare strategies for handling asynchronous operations within Express routes, such as using raw callbacks, Promise chains, and async/await with error handling.

Explain how Express handles errors through dedicated error-handling middleware.

Describe the role of environment variables for configuration management in separating configuration from code.