Advanced TypeScript Patterns for Large-Scale Applications

TypeScript's type system is incredibly powerful, but many developers only scratch the surface. Here are advanced patterns I use in production applications.

Discriminated Unions

Instead of optional properties, use discriminated unions for type-safe handling of different states.

This pattern works great for API responses, form states, and any scenario with mutually exclusive states.

Generic Constraints

Constrain generics to ensure type safety while maintaining flexibility. The extends keyword limits what types can be passed.

Template Literal Types

TypeScript 4.1 introduced template literal types, enabling powerful string manipulation at the type level.

Mapped Types

Transform existing types into new ones. Useful for creating readonly versions, partial types, or picking specific properties.

Type Guards

Narrow types with custom type guards for complex conditions.

Branded Types

Prevent mixing up primitive types that represent different concepts. A UserId shouldn't be assignable to a ProductId, even if both are strings.

Const Assertions

Use as const to narrow literal types and prevent mutation.

Module Augmentation

Extend third-party types without modifying source code. Useful for adding custom properties to library types.

These patterns have helped me maintain large TypeScript codebases with confidence. The compiler catches errors that would otherwise reach production.