TypeScript's type system is incredibly powerful, but many developers only scratch the surface. In this article, we'll explore advanced patterns that can help you build more robust, maintainable applications.

Discriminated Unions

Discriminated unions combine union types with literal types to create a pattern where TypeScript can narrow down the exact type based on a discriminant property. This is extremely useful for modeling state machines and handling different variations of data.

type Result<T, E> =
  | { success: true; data: T }
  | { success: false; error: E };

Generic Constraints

Generic constraints let you limit the types that can be used with generics. This ensures type safety while maintaining flexibility. Use extends to specify that a type parameter must satisfy certain requirements.

• Use extends to constrain generic types
• Combine with keyof for property access
• Create conditional types for advanced scenarios
• Use infer for type extraction

Branded Types

Branded types (also called nominal types) let you create distinct types from primitives. This prevents accidentally mixing up values that have the same underlying type but different semantic meanings.

Branded types catch bugs at compile time that would otherwise only surface at runtime—if you're lucky.

Module Augmentation

Module augmentation allows you to extend existing types from libraries without modifying their source code. This is particularly useful when working with third-party libraries or adding custom properties to global types.

Conclusion

These patterns represent just a fraction of what TypeScript's type system can do. As you become more comfortable with these techniques, you'll find new ways to leverage the type system to catch bugs earlier and express your domain more precisely.