writing-typescript

Discriminated unions combine related states into a single type with explicit variants—like `'idle' | 'loading' | 'success' | 'error'`—instead of separate boolean flags. This ensures all states are accounted for, prevents invalid combinations, and makes exhaustive type checking possible in switch statements.

Use a Result type pattern that explicitly models success and failure outcomes, making errors part of your type signature rather than thrown exceptions. This approach forces callers to handle both cases, integrates cleanly with discriminated unions, and works well in Node.js services and React applications.

Enable strict mode in your tsconfig.json to enforce full type checking across your codebase. Strict mode enforces null checks, property initialization, implicit any elimination, and other rules that catch common bugs at compile time before they reach production.

Interfaces are better for object contracts and public APIs, especially when you need declaration merging; types are more flexible for unions, tuples, and complex shapes. The choice depends on your architecture—this Skill covers both patterns and when each fits real-world project structures.

Yes. Build type-safe React components and hooks using discriminated unions for loading states, Zod for schema validation, and Result types for explicit error handling. TanStack Query integrates cleanly with this pattern to manage async data-fetching state safely.

Use discriminated unions with exhaustive type checking in switch expressions. When all union variants are handled, TypeScript narrows the type to `never` at unreachable branches, so the compiler catches missing cases before runtime.