TypeScript Development (Lean)

When to use

• .ts, .tsx, tsconfig.json
• React/Next.js code paths
• API clients/servers requiring strict typing

Defaults

• Keep strict: true.
• Prefer inferred types unless explicit types improve readability.
• Validate untrusted input with schemas (for example Zod).
• Use discriminated unions instead of boolean mode flags.

Quick workflow

1. Confirm type boundaries (input/output contracts).
2. Implement smallest typed change.
3. Add/update tests.
4. Run type check + lint + test.

Commands

• Install/run (Bun-compatible repos): bun install, bun run <script>
• Type check: bunx tsc --noEmit or npx tsc --noEmit
• Tests: bun test or project test script

Implementation checklist

• No any unless documented and justified.
• Exhaustive branching for tagged unions.
• Public types exported from stable module boundaries.
• Runtime validation for API and form payloads.

Validation checklist

• tsc --noEmit passes.
• Lint passes.
• Tests pass for changed behavior.
• Build output unchanged unless intended.

References

• reference.md - type and architecture patterns
• examples.md - compact TS/React examples
• ../AGENT_SKILL_SPEC.md - shared Anthropic/Copilot alignment