TypeScript Language Patterns

Priority: P0 (CRITICAL)

Implementation Guidelines

• Type Annotations: Explicit params/returns. Infer locals.
• Interfaces vs Types: interface for APIs (supports declaration merging). type for unions, intersection types, mapped/conditional types.
• Strict Mode: strict: true. Null Safety: ?. and ?? — Use narrowing instead. Avoid non-null assertion (!) operator.
• Enums: Literal unions or as const. No runtime enum.
• Generics: Reusable, type-safe code.
• Type Guards: typeof, instanceof, predicates.
• Utility Types: Partial, Pick, Omit, Record.
• Immutability: readonly arrays/objects. Const Assertions: as const, satisfies.
• Template Literals: on${Capitalize<string>}.
• Discriminated Unions: Literal kind property to narrow type safely. Switch on discriminant.
• Advanced: Mapped, Conditional, Indexed types.
• Access: Default public. Use private/protected or #private.
• Branded Types: string & { __brand: 'Id' }.