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

// 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

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}`);
    }
  }
}