TypeScript at Scale
TypeScript has become the default language for frontend and full-stack development at Nexis Limited. Every new project — from our Next.js applications to TanStack Start frontends — uses TypeScript with strict configuration. The type system catches entire categories of bugs at compile time, improves editor tooling, and serves as living documentation of your data structures.
Start with Strict Configuration
Enable strict mode in your tsconfig.json from day one. This activates all strict type-checking options including strictNullChecks, noImplicitAny, and strictFunctionTypes. Adding strict mode to an existing codebase is painful; starting with it is nearly free.
Prefer Interfaces for Object Shapes
Use interfaces for defining object shapes and types for unions, intersections, and utility types. Interfaces are more performant for the compiler, support declaration merging, and produce clearer error messages. Reserve type aliases for cases where interfaces cannot express the shape you need.
Leverage Discriminated Unions
Discriminated unions are one of TypeScript's most powerful features. They allow you to model states that are mutually exclusive in a way that the compiler can verify exhaustively. This is invaluable for state machines, API response handling, and form validation.
Use Zod for Runtime Validation
TypeScript's type system only exists at compile time. Data from external sources — API responses, form inputs, environment variables — needs runtime validation. Zod lets you define a schema once and derive both the runtime validator and the TypeScript type from it, eliminating the risk of type definitions drifting from validation logic.
Avoid Enums; Use Const Objects
TypeScript enums have surprising runtime behavior and generate unnecessary JavaScript. Prefer const objects with as const assertions, which provide the same type safety without runtime overhead. This also plays better with tree-shaking in bundlers.
Utility Types for DRY Code
TypeScript's built-in utility types — Partial, Required, Pick, Omit, Record, Extract, Exclude — reduce duplication by deriving new types from existing ones. For example, a form for creating a user might use Omit<User, 'id' | 'createdAt'> to exclude server-generated fields.
Generic Functions and Components
Generics allow you to write functions and React components that work with any type while preserving type safety. A well-typed generic data table component, for instance, can accept any row type and provide fully typed column definitions, sort functions, and filter handlers.
Conclusion
TypeScript's value scales with application size. The practices outlined here — strict configuration, discriminated unions, runtime validation, and utility types — form the foundation of maintainable TypeScript codebases at any scale.
Building a large TypeScript application? Our team can help with architecture and code quality.