Node.js Backend Engineer Interview Questions & Screening Guide
Technical screening guide for vetting high-performance Node.js, API, and database engineers.
How does the Node.js event loop work, and what happens if you execute CPU-heavy tasks on the main thread?
Event loop phases (timers, poll, check), single-threaded nature, and how synchronous blocking degrades throughput.
"Node.js runs JavaScript on a single thread utilizing an event loop backed by libuv. Heavy CPU tasks like encryption or image resizing block the loop. I offload those to Worker Threads, child processes, or background job queues like BullMQ."
Thinks Node.js runs multi-threaded JavaScript code by default.
How do you manage database transactions to prevent race conditions during concurrent financial updates?
ACID properties, row-level locking (SELECT FOR UPDATE), or optimistic concurrency control.
"I wrap balance deductions in strict database transactions with row-level locks or verify version timestamps using optimistic concurrency control to prevent double-spending."
Reads balance in code, modifies in memory, and writes back without transactional locks.
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