Performance Traps

Event Loop Blocking

• fs.readFileSync blocks entire server — use fs.promises.readFile
• CPU-intensive code blocks — no I/O processed, use worker_threads
• Large JSON.parse blocks — consider streaming parser for big files
• RegEx catastrophic backtracking — /(a+)+$/ hangs on "aaaaaaaaaaaaaaX"

Memory Leaks

• Event listeners accumulate — removeListener or use once()
• setInterval without clearInterval — keeps running forever
• Closures hold references — large objects stay in memory
• Global caches grow unbounded — use LRU with max size

Worker Threads

• Thread creation has overhead — don't spawn per-request, use pool
• postMessage copies data — use SharedArrayBuffer for large data