JavaScript Development (Lean)

When to use

• .js, .mjs, .cjs, package.json
• Node/Bun/Deno runtime work
• API handlers, async flows, test/lint setup

Defaults

• Prefer Bun for install/run/test where compatible.
• Prefer async/await over nested promise chains.
• Keep modules explicit (ESM preferred unless project is CJS).
• Add input validation at API boundaries.

Quick workflow

1. Detect runtime and package manager from repo files.
2. Keep change minimal and idiomatic.
3. Add or update tests near touched behavior.
4. Run lint/tests; report exact commands and outcomes.

Runtime commands

Bun-first

• Install: bun install
• Run script: bun run <script>
• Test: bun test
• One-off: bunx <tool>

Node fallback

• Install: npm install
• Test: npm test
• Type check (TS interop): npx tsc --noEmit

Deno

• Run: deno run -A main.ts
• Test: deno test

Implementation checklist

• Use small pure helpers for transform logic.
• Centralize error handling at service/API boundaries.
• Avoid mutable shared state across async operations.
• Prefer native platform APIs before adding dependencies.

Validation checklist

• Lint and format pass.
• Tests cover changed paths.
• No secrets in code or logs.
• Error messages are actionable.

References

• reference.md - compact runtime/tooling matrix
• examples.md - API/test/config snippets
• ../AGENT_SKILL_SPEC.md - shared Anthropic/Copilot alignment