TypeScript

Rules

Compiler

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true,
    "noImplicitOverride": true,
    "noFallthroughCasesInSwitch": true,
    "verbatimModuleSyntax": true
  }
}

• Extend the framework’s base config (for example Astro’s strict preset) and add the flags above.
• tsc --noEmit (or the framework checker) runs in CI.

Types

• No any. Use unknown and narrow. A justified any has a comment.
• type for data shapes and unions; interface for component props and extendable contracts. Be consistent per project.
• Derive types from schemas (z.infer<typeof schema>) instead of writing them twice.
• Use discriminated unions for state ({ status: 'loading' } | { status: 'error', error } | …).
• Avoid enums with runtime output; prefer string-literal unions or as const objects.

Boundaries

• Validate all external data (API responses, form input, env vars, JSON files) with Zod or similar at the edge.
• Validate environment variables at startup and fail fast.

Tooling

• ESLint with typescript-eslint (recommended + type-checked rules) and Prettier; fail CI on warnings.
• Path aliases in tsconfig (@lib/*, @components/*) instead of ../../../.
• No barrel files re-exporting whole folders in browser code.

Style

• Functions are small and pure where possible; async functions always handle or propagate errors.
• Prefer readonly arrays and properties for data that should not change.

Checklist

• Strict flags on; checker in CI
• No unexplained any
• Types inferred from schemas
• Env vars validated at startup
• ESLint + Prettier clean