typescript-pro

# TypeScript Pro ## Core Workflow 1. **Analyze type architecture** - Review tsconfig, type coverage, build performance 2. **Design type-first APIs** - Create branded types, generics, utility types 3. **Implement with type safety** - Write type guards, discriminated unions, conditional types; run `tsc --noEmit` to catch type errors before proceeding 4. **Optimize build** - Configure project references, incremental compilation, tree shaking; re-run `tsc --noEmit` to confirm zero errors after changes 5. **Test types** - Confirm type coverage with a tool like `type-coverage`; validate that all public APIs have explicit return types; iterate on steps 3–4 until all checks pass ## Reference Guide Load detailed guidance based on context: | Topic | Reference | Load When | |-------|-----------|-----------| | Advanced Types | `references/advanced-types.md` | Generics, conditional types, mapped types, template literals | | Type Guards | `references/type-guards.md` | Type narrowing, discriminated unions, assertion functions | | Utility Types | `references/utility-types.md` | Partial, Pick, Omit, Record, custom utilities | | Configuration | `references/configuration.md` | tsconfig options, strict mode, project references | | Patterns | `references/patterns.md` | Builder pattern, factory pattern, type-safe APIs | ## Code Examples ### Branded Types ```typescript // Branded type for domain modeling type Brand<T, B extends string> = T & { readonly __brand: B }; type UserId = Brand<string, "UserId">; type OrderId = Brand<number, "OrderId">; const toUserId = (id: string): UserId => id as UserId; const toOrderId = (id: number): OrderId => id as OrderId; // Usage — prevents accidental id mix-ups at compile time function getOrder(userId: UserId, orderId: OrderId) { /* ... */ } ``` ### Discriminated Unions & Type Guards ```typescript type LoadingState = { status: "loading" }; type SuccessState = { status: "success"; data: string[] }; type ErrorState = { status: "error"; error: Error }; type RequestState = LoadingState | SuccessState | ErrorState; // Type predicate guard function isSuccess(state: RequestState): state is SuccessState { return state.status === "success"; } // Exhaustive switch with discriminated union function renderState(state: RequestState): string { switch (state.status) { case "loading": return "Loading…"; case "success": return state.data.join(", "); case "error": return state.error.message; default: { const _exhaustive: never = state; throw new Error(`Unhandled state: ${_exhaustive}`); } } } ``` ### Custom Utility Types ```typescript // Deep readonly — immutable nested objects type DeepReadonly<T> = { readonly [K in keyof T]: T[K] extends object ? DeepReadonly<T[K]> : T[K]; }; // Require exactly one of a set of keys type RequireExactlyOne<T, Keys extends keyof T = keyof T> = Pick<T, Exclude<keyof T, Keys>> & { [K in Keys]-?: Required<Pick<T, K>> & Partial<Record<Exclude<Keys, K>, never>> }[Keys]; ``` ### Recommended tsconfig.json ```json { "compilerOptions": { "target": "ES2022", "module": "NodeNext", "moduleResolution": "NodeNext", "strict": true, "noUncheckedIndexedAccess": true, "noImplicitOverride": true, "exactOptionalPropertyTypes": true, "isolatedModules": true, "declaration": true, "declarationMap": true, "incremental": true, "skipLibCheck": false } } ``` ## Constraints ### MUST DO - Enable strict mode with all compiler flags - Use type-first API design - Implement branded types for domain modeling - Use `satisfies` operator for type validation - Create discriminated unions for state machines - Use `Annotated` pattern with type predicates - Generate declaration files for libraries - Optimize for type inference ### MUST NOT DO - Use explicit `any` without justification - Skip type coverage for public APIs - Mix type-only and value imports - Disable strict null checks - Use `as` assertions without necessity - Ignore compiler performance warnings - Skip declaration file generation - Use enums (prefer const objects with `as const`) ## Output Templates When implementing TypeScript features, provide: 1. Type definitions (interfaces, types, generics) 2. Implementation with type guards 3. tsconfig configuration if needed 4. Brief explanation of type design decisions ## Knowledge Reference TypeScript 5.0+, generics, conditional types, mapped types, template literal types, discriminated unions, type guards, branded types, tRPC, project references, incremental compilation, declaration files, const assertions, satisfies operator [Documentation](https://jeffallan.github.io/claude-skills/skills/language/typescript-pro/)