Node.js Developer interview questions

The key patterns for asynchronous programming in Node.js include callback functions, promises, async/await, and event emitters. Senior developers prefer using promises and async/await for cleaner, more readable code, while callbacks are legacy but still encountered. Proper error handling in asynchronous flows and avoiding callback hell through control flow libraries or async/await are essential for robust applications.

Event-driven architecture in Node.js utilizes events and listeners to decouple components, allowing actions to be triggered asynchronously based on emitted events. This model improves scalability by enabling non-blocking I/O, processing multiple operations concurrently, and efficiently managing high loads without thread overhead.

Effective error handling in asynchronous Node.js code involves using error-first callbacks, handling rejections in promises, wrapping async/await calls with try/catch blocks, and centralizing error management with middleware in frameworks like Express. Senior developers also log errors effectively and implement monitoring for unhandled exceptions and rejections.

The event loop in Node.js acts as the core mechanism that handles and processes asynchronous operations. It allows Node.js to perform non-blocking I/O operations by offloading callbacks, event handlers, and timers, ensuring the single-threaded process can serve multiple requests efficiently.

Best practices for designing asynchronous APIs in Node.js include consistently returning promises or using async/await for clarity, avoiding mixing callback and promise patterns, providing meaningful error messages, and ensuring that APIs are non-blocking to maintain responsiveness and scalability.

To prevent race conditions in asynchronous JavaScript, senior developers use techniques such as careful sequencing of operations, using promise chaining or async/await, leveraging mutexes or locking libraries for critical sections, and avoiding shared mutable state whenever possible.

Main challenges include managing inconsistent callback or promise patterns, handling errors across different libraries, ensuring resource cleanup, resolving potential event emitter leaks, and abstracting third-party logic to avoid tight coupling. Senior developers often write adapters or wrappers for consistency.

Senior Node.js developers utilize built-in debuggers, advanced logging with correlation IDs, async stack trace tools, and platforms like Node Inspector or ndb. Structured logging, tracing asynchronous code flow, and thorough test coverage are also vital for troubleshooting asynchronous and event-driven code.

Blocking code prevents the event loop from processing further events, degrading performance and scalability. To avoid blocking, developers offload compute-intensive tasks to worker threads or external services, write non-blocking asynchronous code, and avoid synchronous APIs for file or network I/O.

Event emitters enable decoupling of components and flexible, asynchronous communication. Benefits include improved modularity and scalability, while trade-offs involve potential event leaks, increased debugging complexity, and harder traceability of code flow. Senior developers mitigate issues with documentation and careful event management.