lang-typescript

Type-safe TypeScript uses strict mode and appropriate type primitives—interfaces, unions, and branded types—to validate data shapes and prevent runtime errors. This Skill guides you through type decision trees and best practices to select the right pattern for each problem, from object validation to discriminated unions.

Interfaces and types serve different purposes: interfaces define object contracts and support declaration merging, while types offer greater flexibility for unions, intersections, and primitives. This Skill explains when each is appropriate and shows examples of common pitfalls to avoid.

Runtime validation ensures external data conforms to your type definitions before your code uses it. This Skill covers patterns like branded types and discriminated unions that bridge compile-time types and runtime checks, with guidance on configuring tsconfig for strict validation.

Discriminated unions use a shared literal field to narrow types safely and exhaustively. They prevent invalid state combinations and improve type inference. This Skill demonstrates their structure and contrasts them with other union patterns for handling multiple data shapes.

Branded types attach compile-time metadata to primitives without runtime overhead, creating nominal distinction between semantically different values. This Skill shows how to apply branding to prevent accidental misuse of IDs, emails, or currency values across your codebase.