node

## When to use

Use this skill whenever you are dealing with Node.js code to obtain domain-specific knowledge for building robust, performant, and maintainable Node.js applications.

## TypeScript with Type Stripping

When writing TypeScript for Node.js, use **type stripping** (Node.js 22.6+) instead of build tools like ts-node or tsx. Type stripping runs TypeScript directly by removing type annotations at runtime without transpilation.

Key requirements for type stripping compatibility:
- Use `import type` for type-only imports
- Use const objects instead of enums
- Avoid namespaces and parameter properties
- Use `.ts` extensions in imports

**Minimal example** — a valid type-stripped TypeScript file:

```ts
// greet.ts
import type { IncomingMessage } from 'node:http';

const greet = (name: string): string => `Hello, ${name}!`;
console.log(greet('world'));
```

Run directly with:
```bash
node greet.ts
```

See [rules/typescript.md](rules/typescript.md) for complete configuration and examples.

## Common Workflows

For multi-step processes, follow these high-level sequences before consulting the relevant rule file:

**Graceful shutdown**: Register signal handlers (SIGTERM/SIGINT) → stop accepting new work → drain in-flight requests → close external connections (DB, cache) → exit with appropriate code. See [rules/graceful-shutdown.md](rules/graceful-shutdown.md).

**Error handling**: Define a shared error base class → classify errors (operational vs programmer) → add async boundary handlers (`process.on('unhandledRejection')`) → propagate typed errors through the call stack → log with context before responding or crashing. See [rules/error-handling.md](rules/error-handling.md).

**Diagnosing flaky tests**: Isolate the test with `--test-only` → check for shared state or timer dependencies → inspect async teardown order → add retry logic as a temporary diagnostic step → fix root cause. See [rules/flaky-tests.md](rules/flaky-tests.md).

**Diagnosing stuck processes/tests** (`node --test` hangs, "process did not exit", CI timeout, open handles): isolate file/test → run with explicit timeout/reporter → inspect handles via `why-is-node-running` (`SIGUSR1`) → patch deterministic teardown in resource-creation scope → rerun isolated + full suite until stable. See [rules/stuck-processes-and-tests.md](rules/stuck-processes-and-tests.md).

**Profiling a slow path**: Reproduce under realistic load → capture a CPU profile with `--cpu-prof` → identify hot functions → check for stream backpressure or unnecessary serialisation → validate improvement with a benchmark. See [rules/profiling.md](rules/profiling.md) and [rules/performance.md](rules/performance.md).

## High-priority activation checklist (streams + caching)

When the task mentions **CSV**, **ETL**, **ingestion pipelines**, **large file processing**, **backpressure**, **repeated lookups**, or **deduplicating concurrent async calls**, explicitly apply this checklist:

1. Use `await pipeline(...)` from `node:stream/promises` (prefer this over chained `.pipe()` in guidance/code).
2. Include at least one explicit `async function*` transform when data is being transformed in-stream.
3. Choose a cache strategy when repeated work appears:
   - `lru-cache` for bounded in-memory reuse in a single process.
   - `async-cache-dedupe` for async request deduplication / stale-while-revalidate behavior.
4. Show where backpressure is handled (implicitly via `pipeline()` or explicitly via `drain`).

### Integrated example pattern (CSV/ETL)

For CSV/ETL-style prompts, prefer an answer structure like:
- `createReadStream(input)`
- `async function*` parser/transform
- optional cached enrichment lookup (`async-cache-dedupe` or `lru-cache`)
- `await pipeline(...)` to a writable destination

Link relevant rules directly in explanations so models can retrieve details:
- [rules/streams.md](rules/streams.md)
- [rules/caching.md](rules/caching.md)

## How to use

Read individual rule files for detailed explanations and code examples:

- [rules/error-handling.md](rules/error-handling.md) - Error handling patterns in Node.js
- [rules/async-patterns.md](rules/async-patterns.md) - Async/await and Promise patterns
- [rules/streams.md](rules/streams.md) - Working with Node.js streams
- [rules/modules.md](rules/modules.md) - ES Modules and CommonJS patterns
- [rules/testing.md](rules/testing.md) - Testing strategies for Node.js applications
- [rules/flaky-tests.md](rules/flaky-tests.md) - Identifying and diagnosing flaky tests with node:test
- [rules/stuck-processes-and-tests.md](rules/stuck-processes-and-tests.md) - Diagnosing processes that do not exit and tests that get stuck
- [rules/node-modules-exploration.md](rules/node-modules-exploration.md) - Navigating and analyzing node_modules directories
- [rules/performance.md](rules/performance.md) - Performance optimization techniques
- [rules/caching.md](rules/caching.md) - Caching patterns and libraries
- [rules/profiling.md](rules/profiling.md) - Profiling and benchmarking tools
- [rules/logging.md](rules/logging.md) - Logging and debugging patterns
- [rules/environment.md](rules/environment.md) - Environment configuration and secrets management
- [rules/graceful-shutdown.md](rules/graceful-shutdown.md) - Graceful shutdown and signal handling
- [rules/typescript.md](rules/typescript.md) - TypeScript configuration and type stripping in Node.js