TypeScript Design Patterns for Scalable Applications

Repository Pattern with Prisma

Abstract your data layer behind repositories. Instead of scattering Prisma calls through components, create typed repository modules for users, workspaces, and subscriptions. This makes testing trivial and lets you swap the database or ORM without touching business logic.

• Define interfaces for every repository
• Return domain entities, not raw database rows
• Inject repositories through function parameters for testability

Type-Safe API Design

Shared types between the frontend and backend eliminate a whole class of bugs. Define Zod schemas for every request and response, infer TypeScript types from them, and validate at the route boundary. Contract-first development pays off the moment the app grows beyond a few screens.

Strategy and Dependency Injection

Provider-based patterns let you swap AI providers, payment gateways, and email services without touching call sites. Define a common interface, implement adapters for OpenAI, Gemini, and Claude, and select the strategy at runtime — exactly how multi-provider AI SaaS platforms work.

Discriminated Unions for State

Model complex states with discriminated unions instead of booleans. A booking that is 'pending', 'confirmed', or 'completed' is safer represented as a union with a discriminant. TypeScript then exhaustively checks every branch, catching impossible states at compile time.