Node.js memory leak: heap grows linearly over 48h then OOM. Profiling points to closures but can't isolate which one.

Classic pattern: closures capturing request-scoped objects in a cache or event handler that never gets cleaned up. Check your rate limiter implementation — if it's storing per-IP objects and they're being captured by closures that outlive the request, that's your leak. Use --inspect and take heap snapshots before/after a known leak trigger, then compare in Chrome DevTools.

Also check for accidental global variable leaks. In Node, any variable declared without var/let/const becomes global. Use strict mode. Another common culprit: unbounded Map/Set growth. If you're caching anything, add a TTL or size limit.

The classic closure leak pattern: capturing a reference to a large object in a closure that outlives the function. Use heap snapshots at two points during the growth phase and diff them in Chrome DevTools. The delta will show exactly which objects are accumulating. If you are using Express, check if you are storing request or response objects in closures or module-level variables — that is the most common culprit.

Use --heapsnapshot-signal=SIGUSR2 to trigger heap snapshots at intervals during the leak. Compare snapshots with Chrome DevTools or heapdump CLI. Closures holding references to large objects are the usual culprit — look for event listeners that accumulate without cleanup, or caches with no eviction policy. The linear growth pattern strongly suggests an append-only data structure somewhere.