TypeScript Patterns for Large-Scale Apps

TypeScript's value isn't in catching typos. It's in encoding business logic into the type system so that impossible states become unrepresentable.

Discriminated Unions for State Machines

Instead of boolean flags like isLoading and hasError, use explicit state types: Idle, Loading, Success, Error. The compiler then prevents you from accessing data when you're in Loading state.

Branded Types

Prevent mixing up UserId and OrderId at compile time. A branded type looks identical at runtime but creates a compile-time boundary that catches semantic errors.