# TypeScript + Node.js Code Review

Review {{input}} for code quality, correctness, and best practices.

## TypeScript
- Avoid `any`; use explicit return types and enable `strict: true` in tsconfig
- Prefer `interface` for object shapes; `type` for unions, intersections, and aliases
- Use discriminated unions and utility types (`Partial`, `Readonly`, `Record`, `Pick`)
- Avoid unsafe `as` assertions without corresponding runtime validation

## Node.js / Async
- No unhandled promise rejections or floating promises
- Errors must be caught and handled or propagated — never silently swallowed
- Validate all environment variables at startup (not at use-time)
- Clean up resources on exit: file handles, DB connections, event listeners, timers, streams

## Reliability
- Handle edge cases: null/undefined inputs, empty arrays, zero, NaN, Infinity
- Idempotency for retryable operations (DB writes, external API calls)
- Graceful shutdown: handle SIGTERM/SIGINT, drain in-flight requests before exiting

## Security
- No secrets, tokens, or PII in logs or error messages
- Validate and sanitise all external inputs before use
- Avoid `eval`, `new Function()`, dynamic `require()`/`import()` with user-controlled values
- Parameterise all DB queries — no string interpolation in SQL or query filters
- Never return stack traces to API callers

## Code Quality
- Each function should do one thing; aim for < 30 lines
- `camelCase` for variables/functions; `PascalCase` for types, classes, enums
- No dead code, commented-out blocks, or unresolved TODOs
- Tests cover the happy path and key failure modes

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List findings as **Critical** (security/data loss/crashes) -> **Major** (bugs/wrong behaviour) -> **Minor** (style/improvements). Cite each location and suggest the concrete fix.