typescript

name	typescript
description	TypeScript development patterns, type system mastery, and best practices.
globs	["**/*.ts","**/*.tsx","**/tsconfig.json"]
priority	95
tags	["language"]

TypeScript Best Practices

Type System

• Prefer interface for object shapes, type for unions/intersections
• Use unknown over any — force type narrowing
• Use discriminated unions for state machines
• Use as const for literal types
• Use satisfies to validate without widening
• Use template literal types for string patterns
• Avoid type assertions (as) — use type guards instead

Generics

• Use constraints: <T extends BaseType>
• Use infer in conditional types for extraction
• Use mapped types for transformations
• Use Record<K, V> for dictionaries
• Use Partial<T>, Required<T>, Pick<T, K>, Omit<T, K>

Error Handling

• Use Result/Either pattern: type Result<T, E> = { ok: true; value: T } | { ok: false; error: E }
• Use branded types for validation: type Email = string & { __brand: 'Email' }
• Use never for exhaustive checks
• Define error types explicitly

Patterns

• Use zod/valibot for runtime validation
• Use barrel exports (index.ts) for modules
• Use path aliases in tsconfig
• Enable strict mode always
• Use noUncheckedIndexedAccess for safety