TypeScript Coding Standards

Core Rules

• TS strict mode. Zero any. Zero untyped exports.
• Explicit return types on all exported functions.
• Interfaces for object shapes. Type aliases for unions/intersections.
• Async/await over raw promises. Always try/catch with typed errors.
• Optional chaining (?.) and nullish coalescing (??) over manual null checks.
• Never use non-null assertion (!) unless justified with a comment.
• const by default. let only when value changes. Never var.
• Destructuring for cleaner code. Template literals for string interpolation.

File Limits

• Functions: <40 lines. Extract if exceeding.
• Files: <300 lines. Split if exceeding.
• No dead code. No unused imports. No commented-out blocks.

Naming

• Components: PascalCase (UserDashboard.tsx)
• Utilities: kebab-case (date-formatter.ts)
• Services: kebab-case (booking.service.ts)
• Types: kebab-case (user.types.ts)
• Tests: .test.ts or .spec.ts
• Constants: SCREAMING_SNAKE_CASE
• Enums: PascalCase with SCREAMING_SNAKE_CASE values

Exports

• Named exports preferred over default exports.
• Barrel exports (index.ts) for module directories.
• JSDoc on every exported function.

Error Handling

• Custom error classes: ValidationError, NotFoundError, UnauthorizedError, ConflictError
• Always log with context (userId, bookingId, etc.)
• Never expose internal errors to clients
• Consistent API response format: { success: boolean, data?: T, error?: { code, message } }