TypeScript Beyond the Basics

TypeScript's type system is remarkably powerful — far beyond simple type annotations. Advanced patterns enable type-safe API layers, exhaustive pattern matching, and compile-time validation of business logic. At Nexis Limited, TypeScript powers all our frontend applications and Next.js backends, and we use advanced patterns to catch bugs before they reach production.

Discriminated Unions

Discriminated unions model data that can be one of several types, each with a discriminant property. TypeScript narrows the type based on the discriminant, providing type-safe access to variant-specific properties.

For example, an API response can be modeled as a union of Success and Error types, with a "status" field as the discriminant. When you check status === "success", TypeScript knows the data field exists. When status === "error", TypeScript knows the message field exists. This eliminates an entire class of null/undefined errors.

Template Literal Types

Template literal types create string types from combinations of other types. You can define event handler names like "onClick", "onHover", "onFocus" programmatically from a union of events. This is particularly useful for API route builders, CSS utility generators, and configuration key validation.

Conditional Types

Conditional types select a type based on a condition, similar to ternary expressions but for types. Combined with infer, they can extract types from complex structures. Common use cases include extracting return types of functions, element types of arrays, and resolving promise types.

Branded Types

Branded types prevent mixing values that have the same underlying type but different semantic meanings. A UserId and a ProductId are both strings, but passing a ProductId where a UserId is expected is a bug. Branded types create distinct types that TypeScript treats as incompatible, catching these mix-ups at compile time.

Type-Safe API Layers

Build API client layers where TypeScript validates request parameters, URL paths, and response types at compile time. Libraries like tRPC and Zodios provide end-to-end type safety between backend and frontend. The server defines the API shape, and the client automatically inherits all types — no manual type definitions, no runtime type mismatches.

Exhaustive Pattern Matching

Use the never type to ensure switch statements handle all possible cases. If a new variant is added to a union type and the switch statement is not updated, TypeScript produces a compile error. This prevents bugs when data models evolve.

Utility Types for Common Patterns

  • Partial<T>: All properties optional — useful for update operations.
  • Required<T>: All properties required — useful for creation operations.
  • Pick<T, K>: Select specific properties — useful for API response subsets.
  • Omit<T, K>: Remove specific properties — useful for removing internal fields from public types.
  • Record<K, V>: Create an object type from key and value types — useful for lookup tables.

Best Practices

  • Prefer interfaces for object shapes that may be extended. Use type aliases for unions, intersections, and computed types.
  • Avoid any — use unknown with type guards instead.
  • Enable strict mode in tsconfig.json for maximum type safety.
  • Use satisfies operator (TypeScript 4.9+) for type validation without widening.
  • Colocate types with the code that uses them rather than maintaining separate type files.

Conclusion

TypeScript's advanced type features are not academic exercises — they prevent real production bugs. Discriminated unions, branded types, and exhaustive pattern matching catch errors that tests might miss. Invest in learning these patterns, and your TypeScript code will be more robust and self-documenting.

Building a TypeScript application? Our team uses TypeScript extensively across frontend and backend.