typescript-conventions

name	typescript-conventions
description	TypeScript and React coding conventions for CAST projects. Load when writing, reviewing, or debugging TypeScript/TSX/React code. Covers file naming, type patterns, hooks, component conventions, and testing approach.
user-invocable	false
allowed-tools	[]

TypeScript Conventions

• Use React 19 patterns: functional components, hooks, no class components
• Extend existing types rather than type casting: type UserAdmin = User & { isAdmin: true } instead of (user as UserAdmin)
• Component files: PascalCase (UserProfile.tsx)
• Hook files: camelCase prefixed with use (useLocalStorage.ts)
• Test files live alongside source: Foo.tsx -> Foo.test.tsx
• Use Vitest + React Testing Library for tests (not Jest in Vite projects)
• Test behavior with getByRole/getByText, not getByTestId
• Import order: React, third-party, local modules, types (enforce with ESLint)
• Prefer interface over type for object shapes that may be extended
• Use satisfies operator for type-safe config objects