TypeScript Advanced Types

Goal

Use advanced types to improve safety without making code unreadable. Prefer simple types until complexity pays for itself.

Rules

• Use unknown instead of any when input is not trusted.
• Let TypeScript infer simple types.
• Add generics only when a type must connect multiple positions.
• Prefer unions and discriminated unions for variants.
• Prefer interface for object shapes.
• Use type for unions, conditionals, mapped types, and aliases.
• Avoid deeply nested conditional or recursive types.
• Add type tests for reusable utilities when the project supports them.

Core Tools