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MesteriisMesteriis/Engineering-Bible-AI/skills/typescript/SKILL.md

typescript

Skill0 starsChanged 4 months agoMITView on GitHub

Applies TypeScript/JavaScript rules for types, async behavior, APIs, tooling, tests, and architecture.

We split this skill into the rules it gives an agent

26 rules. 0 are common, 22 are distinctive, and 4 are very specific to this project.

  • 0

    Common

    Most of the 51 edited versions we read keep these.

  • 22

    Distinctive

    This author's own choices. Worth a look.

  • 4

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Before changing TypeScript/JavaScript code, inspect relevant files when present:

    line 14
  2. Distinctive:

    Do not mix package managers.

    line 37
  3. Distinctive:

    Follow existing module style.

    line 41
  4. Distinctive:

    Prefer explicit types at boundaries.

    line 42
  5. Very specific:

    Avoid utils dumping grounds.

    line 44
  6. Distinctive:

    Avoid mutation-heavy shared state.

    line 45
  7. Distinctive:

    Avoid hidden singleton state unless project architecture intentionally uses it.

    line 46
  8. Distinctive:

    Keep framework-specific code at framework boundaries.

    line 47
  9. Very specific:

    Avoid any unless justified.

    line 52
  10. Very specific:

    Use unknown instead of any for untrusted data, then narrow.

    line 53
  11. Distinctive:

    Prefer discriminated unions for state machines and variant data.

    line 54
  12. Distinctive:

    Prefer explicit return types for exported functions.

    line 55
  13. Distinctive:

    Do not silence type errors with broad assertions.

    line 56
  14. Very specific:

    Avoid as casts unless narrowing cannot express the invariant.

    line 57
  15. Distinctive:

    Do not assume TypeScript types validate runtime data.

    line 62
  16. Distinctive:

    use existing schema/validation library if present.

    line 67
  17. Distinctive:

    do not introduce a new validator unless justified.

    line 68
  18. Distinctive:

    If UI code is present:

    line 73
  19. Distinctive:

    keep side effects explicit.

    line 78
  20. Distinctive:

    avoid over-abstraction for tiny components.

    line 79
  21. Distinctive:

    If backend code is present:

    line 84
  22. Distinctive:

    keep route handlers thin;

    line 86
  23. Distinctive:

    avoid leaking internal errors.

    line 88
  24. Distinctive:

    avoid blocking expensive work in request paths.

    line 90
  25. Distinctive:

    keep persistence and business rules separated according to project architecture.

    line 91
  26. Distinctive:

    Use existing test tooling.

    line 95

“Common” is measured: kept by at least 6 in 10 of the 51 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Skill: typescript

Purpose

Apply the shared engineering style to TypeScript and JavaScript projects while respecting existing tooling and architecture.

Inspect First

Before changing TypeScript/JavaScript code, inspect relevant files when present:

  • package.json
  • tsconfig.json
  • eslint.config.*
  • .eslintrc*
  • prettier.config.*
  • .prettierrc*
  • vite.config.*
  • next.config.*
  • webpack.config.*
  • vitest.config.*
  • jest.config.*
  • lockfiles
  • existing source and tests

Package manager detection:

  • pnpm-lock.yaml -> use pnpm
  • yarn.lock -> use yarn
  • package-lock.json -> use npm
  • bun.lockb / bun.lock -> use bun only if project uses it

Do not mix package managers.

Style

  • Follow existing module style.
  • Prefer explicit types at boundaries.
  • Keep modules cohesive.
  • Avoid utils dumping grounds.
  • Avoid mutation-heavy shared state.
  • Avoid hidden singleton state unless project architecture intentionally uses it.
  • Keep framework-specific code at framework boundaries.

TypeScript Rules

  • Prefer strict types.
  • Avoid any unless justified.
  • Use unknown instead of any for untrusted data, then narrow.
  • Prefer discriminated unions for state machines and variant data.
  • Prefer explicit return types for exported functions.
  • Do not silence type errors with broad assertions.
  • Avoid as casts unless narrowing cannot express the invariant; explain non-obvious casts.
  • Respect existing runtime validation strategy.

Runtime Validation

Do not assume TypeScript types validate runtime data.

For external input:

  • validate at boundaries;
  • use existing schema/validation library if present;
  • do not introduce a new validator unless justified;
  • handle invalid data explicitly.

React / UI Code

If UI code is present:

  • keep components cohesive;
  • avoid god components;
  • separate state management, data fetching, and presentation when complexity justifies it;
  • keep side effects explicit;
  • avoid over-abstraction for tiny components;
  • preserve accessibility behavior.

Node / Backend Code

If backend code is present:

  • keep route handlers thin;
  • validate input;
  • avoid leaking internal errors;
  • propagate cancellation/timeouts where supported;
  • avoid blocking expensive work in request paths;
  • keep persistence and business rules separated according to project architecture.

Tests and Validation

Use existing test tooling.

Common commands, only when configured or clearly available:

pnpm test
pnpm lint
pnpm typecheck
npm test
npm run lint
npm run typecheck
yarn test
yarn lint
yarn typecheck
bun test

Report exact commands and results.

Shared Cross-Ecosystem Style

Apply the shared engineering style from:

  • ../../engineering/05_design_principles.md
  • ../../engineering/06_responsibility_model.md
  • ../../engineering/07_complexity_budget.md
  • ../../engineering/12_naming_bible.md

Language-specific idioms control syntax and ecosystem details, but they must not weaken the core rules: small cohesive units, explicit boundaries, honest validation, no dumping grounds, and no fake placeholders.

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