End-to-End Type Safety in TypeScript for software

1. I used to copy-paste types between my frontend and backend until I shipped a bug that cost us $10k. The API response changed from userId to user_id, but I only updated the backend interface. My Next.js frontend kept expecting the old property name, silently failing for weeks until customers complained about broken user profiles.

2. I discovered monorepos aren't just for Google-scale companies—they're a lifesaver for type sharing. Setting up a shared @myapp/types package in my workspace meant I could import the same User, Order, and Product interfaces in both my Express API and Next.js frontend. One source of truth, zero drift

3. I learned the hard way that CommonJS and ESM module systems don't play nice when sharing types. My NestJS backend used CommonJS while my Vite-powered frontend expected ESM. I spent three days debugging import errors before realizing I needed to configure my shared package to export both formats

4. Server actions in Next.js 14 changed everything—I could finally share types without network boundaries. Instead of maintaining separate API types and client types, my server actions let me pass complex TypeScript objects directly from server to client. No more manual serialization or prayer that my API contracts stayed in sync

5. I built my own type validation layer using Zod schemas that worked on both ends. Every API endpoint validated incoming data against the same schema that my frontend forms used. When the schema changed, both sides broke at compile time instead of silently failing in production.

6. I realized tRPC was like having a personal assistant for type safety. Setting it up with my Next.js app meant my frontend autocompleted my backend functions, complete with parameter types and return values. Refactoring the backend instantly updated every frontend call site.

7. I created a shared utilities package that included not just types, but validation functions and constants. My @myapp/shared package exported everything from UserRole enums to validateEmail() functions. Both my API middleware and frontend forms used identical validation logic.

8. I discovered that Next.js App Router's built-in type safety was almost magical. Server components could fetch data and pass complex objects like Date and Map directly to client components without serialization. My types flowed seamlessly from database queries to UI components.

9. I learned to use OpenAPI code generation as a backup for third-party APIs. While my own services used shared TypeScript types, external APIs needed a different approach. Code generation from OpenAPI specs kept my frontend types in sync with partner services without manual maintenance.

10. I now sleep better knowing that breaking changes fail fast at build time, not in production. My entire stack—from database models to UI components—shares the same type definitions. When I change a property name, TypeScript errors guide me to every place that needs updating. Type safety isn't just about catching bugs; it's about fearless refactoring.