typescript-conventions

name	typescript-conventions
description	TypeScript code conventions covering strict tsconfig, ESM imports, discriminated unions, formatting/linting, Vitest testing, lockfile-based packaging, Node.js, and security. Load when writing or reviewing TypeScript code.

• strict: true + noUncheckedIndexedAccess in tsconfig, never any — use unknown with type guards.
• ESM imports only, const over let, as const for literals, interface over type for objects.
• import type for type-only imports to avoid runtime overhead. Discriminated unions for type-safe state.
• Formatting/linting: a formatter + linter (e.g., Prettier + ESLint, or Biome). Type checking: tsc --noEmit in CI.
• Testing: a fast test runner (e.g., Vitest or Jest), 80%+ coverage. Runtime validation at system boundaries with a schema validator (e.g., Zod).
• Error handling: discriminated unions for expected errors, throw only for unexpected.
• Package manager: a lockfile-based package manager (npm, pnpm, or yarn) with the lockfile committed, build: a bundler (e.g., tsup or esbuild).
• Monorepo: workspace protocol (workspace:*), shared tsconfig base, a workspace manifest (e.g., pnpm-workspace.yaml).
• Node.js: node: prefix for core modules, fetch over axios.
• Security: npm audit/pnpm audit for dependency CVE scanning. Zero tolerance for critical/high vulnerabilities.
• Anti-patterns: non-null assertions (!), type assertions (as), enum (use unions), @ts-ignore.