TypeScript Utility Types Explorer

Utility types are built-in TypeScript generic types that transform existing types into new ones. They cover common type-level operations like making all properties optional (Partial<T>), required (Required<T>), readonly (Readonly<T>), picking a subset of keys (Pick<T, K>), or omitting keys (Omit<T, K>). They eliminate the need to manually rewrite type definitions.

Use Partial<T> when creating update/patch payloads where not all fields are required (e.g., API PATCH requests). Use Required<T> to strip optional markers and force all fields to be present — useful for form validation output types or after hydrating optional config with defaults.

Pick<T, K> creates a new type with only the specified keys K from T. Omit<T, K> creates a type with all keys from T except K. Use Pick when you want a small subset of a large type. Use Omit when you want everything except a few fields — especially useful for removing 'id' or 'createdAt' from database entity types in create payloads.

Exclude<T, U> removes types from union T that are assignable to U. Extract<T, U> keeps only types from union T that are assignable to U. Example: Exclude<'a'|'b'|'c', 'a'|'b'> results in 'c'. These operate on union type members, unlike Omit/Pick which operate on object keys.

ReturnType<T> extracts the return type of a function type T. Parameters<T> extracts the parameter types as a tuple. These are invaluable for typing wrappers, middleware, and decorators without duplicating type annotations. Example: if you have an API handler, ReturnType<typeof handler> gives you its response type automatically.