Node.js & Elysia Vibe Code Cleanup

Event Loop Crimes AI Commits in Every Handler

AI doesn’t respect the event loop. It’s the single most important concept in Node.js, and AI ignores it consistently. It generates fs.readFileSync in request handlers. It runs CPU-intensive JSON parsing on the main thread. It uses for loops over large arrays where a stream would work. Each blocking operation freezes every concurrent request. Your API goes from fast to unresponsive because one endpoint does something synchronous.

Error handling is either missing or broken. AI generates try-catch blocks that catch errors and log them but don’t propagate them. Promises are created without .catch() handlers. Async functions throw errors that nobody awaits. In development, these are silent. In production, unhandledRejection kills your process. You see random restarts in your process manager logs and no clear cause.

Elysia-specific issues compound the problem. AI doesn’t use Elysia’s plugin system for shared concerns like authentication, logging, or rate limiting. Instead, it duplicates middleware logic across routes. It ignores Elysia’s built-in type validation through TypeBox and does manual checks in route handlers. The type safety Elysia provides for free goes unused.

Memory leaks are the slow killer. AI registers event listeners without removing them. It creates closures that capture request-scoped data in module-level caches. It opens database connections or file handles without cleanup paths. Memory grows 10MB per hour. Your ops team restarts the service daily because nobody knows where the leak is.

Flame Graphs, Worker Threads, and Elysia Plugins

We profile the event loop first. Using clinic.js and 0x, we generate flame graphs that show exactly where time is spent. Blocking calls stand out immediately - they’re the wide bars that shouldn’t exist in an async application. Every synchronous file operation, CPU-heavy computation, and blocking library call gets identified.

Blocking operations move off the main thread. File operations become async. CPU-intensive work moves to worker threads. Large data processing uses streams instead of loading everything into memory. We verify with the blocked-at package, which alerts if the event loop is blocked for more than a configurable threshold.

Error handling gets a complete overhaul. We implement Elysia’s onError lifecycle hook as the global error boundary. Every route gets proper error typing. Business errors use custom error classes with status codes. Validation errors return structured messages. Unexpected errors return a generic message - never a stack trace. Every async operation has explicit error handling.

Elysia’s plugin system replaces duplicated middleware. Authentication becomes a plugin that decorates the context. Rate limiting is a plugin with configurable limits per route group. Logging is a plugin that captures request timing, status codes, and error details. Each plugin is tested in isolation and composed at the app level.

From Daily Restarts to Weeks of Uptime

Before: An API that handles 200 requests per second before the event loop lag exceeds 100ms. Memory grows 15MB per hour and requires daily restarts. Unhandled rejections cause 3-4 random crashes per week. Error responses include file paths and line numbers from stack traces.

After: The same API handles 2,000 requests per second with event loop lag under 5ms. Memory stays flat for weeks. Zero unhandled rejection crashes. Error responses are structured, informative for clients, and safe for production.

The monitoring dashboard tells the story. Before, event loop delay looks like a sawtooth - spikes during traffic, never fully recovering. After, it’s a flat line near zero regardless of load. Memory graphs go from an upward slope to a flat line.

CI Load Tests and Heap Snapshots That Catch Leaks Early

We configure clinic.js to run in CI against a representative load test. If event loop delay exceeds the threshold or if memory grows during the test, the pipeline fails. AI-generated code that blocks the event loop gets caught before deployment.

ESLint rules target Node.js-specific anti-patterns. no-sync flags synchronous filesystem calls. no-floating-promises catches unawaited async calls. Custom rules flag event listener registration without corresponding removal. These run in pre-commit hooks.

Elysia’s type system becomes the enforcement layer. Route schemas define request and response types using TypeBox. If a route handler returns data that doesn’t match the response schema, TypeScript catches it at compile time. No runtime surprises. No mismatched API contracts.

We add heap snapshot comparison tests. A test takes a heap snapshot, runs a batch of requests, takes another snapshot, and asserts that retained memory growth is within bounds. This catches the memory leaks AI introduces with closures, event listeners, and unclosed resources before they reach production.