Node.js backend development for APIs, services, and server infrastructure.

Node.js's event loop model creates specific failure modes that don't exist in multi-threaded runtimes:

Blocking the event loop: Synchronous CPU-heavy operations (large JSON parsing, regex, crypto without worker_threads) block all requests. Node.js is single-threaded — blocking code blocks everything.

Unhandled promise rejections: In older Node.js: unhandled rejections were silently ignored. In modern Node.js: they terminate the process. Every promise chain needs a .catch() or must be awaited in a try-catch.

Memory leaks: Closures that hold references to large objects, event listeners that accumulate without removal, module-level data structures that grow indefinitely. Node.js processes that grow in memory over time.

Async/await error handling:

// Wrong — silent failure
const data = await fetch(url);
// Right
try {
  const data = await fetch(url);
} catch (error) {
  // Handle network errors
}

Connection pool exhaustion: Database connection pools (Postgres, Redis) have limits. Code that creates connections without releasing them exhausts the pool under load.