Shared

The shared/ directory contains code that can run on both the client and the server. Because it must work in either environment, shared code is restricted to native JavaScript — no Node.js built-ins, no browser globals, no environment-specific dependencies.

Think of the shared layer as a pure logic layer: data structures, validation schemas, utility functions, and base service classes that have no side effects tied to a specific runtime.

What belongs here

• Base service classes (extended separately on client and server)
• Validation schemas (e.g. Valibot)
• Pure utility functions
• Shared TypeScript types and interfaces
• Serialization and transformation helpers

What does not belong here

• fs, path, crypto, or any other Node.js built-in
• window, document, localStorage, or any browser API
• Direct imports from server/ or client/
• Any library that has different behaviour depending on the runtime

Why this separation matters

Keeping shared code free of runtime assumptions means the same logic can be used for server-side validation, client-side validation, and SSR without any conditional shims or bundler hacks.