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Advanced Types

Creating Custom Utility Types

Master designing custom utility types in TypeScript, combining mapped types, conditional types, template literals, and key remapping for advanced domain architecture.

Last Updated: July 29, 2026 • 10 min read

While TypeScript includes standard utility types (Partial, Omit, ReturnType), complex applications frequently require Custom Utility Types tailored to specific codebase conventions.

Custom utility types are built by composing Generics, Mapped Types, Conditional Types, Indexed Access Types, and Template Literals.

1. Custom Utility 1: DeepPartial

Standard Partial is shallow. DeepPartial recursively turns all nested properties into optional properties:

2. Custom Utility 2: RequireAtLeastOne

Forces an object type to include at least one of its properties:

3. Custom Utility 3: Mutable (Remove Readonly)

Removes readonly modifiers from all properties:

4. Interactive Code Playground

Test custom utility types below:

5. Summary Checklist

  • [x] Compose generic parameters with mapped types [K in keyof T] for object transformations.
  • [x] Use recursive conditional types (extends object ? Custom : T[P]) for deep object traversal.
  • [x] Use key remapping as to filter properties (as T[K] extends Type ? K : never).