TypeScript Patterns for Large Codebases: Generics, Discriminated Unions & Module Boundaries

TypeScript has become the industry standard for scalable JS apps. Understanding high-level patterns like Generics and Utility Types is key to building durable systems.

The Power of Generics

Generics allow you to create components and functions that work over a variety of types rather than a single one. This leads to much more reusable and type-safe utilities.

interface ApiResponse<T> {
  data: T;
  error: string | null;
}

// Usage with a specific user type
const response: ApiResponse<User> = await fetchUser();

Mapped and Conditional Types

Advanced features like 'Partial', 'Pick', and conditional types allow you to transform existing types into new ones, maintaining a single source of truth for your data models.