How does this skill improve TDD workflows?

During the refactor phase of TDD, this skill helps identify repeating logic in tests and provides a standardized structure to move that logic into centralized Entity Objects.

Why does the pattern use a layered structure?

The layered structure (Base, Derived, Composite) ensures that logic flows in one direction, preventing circular dependencies and making the code easier to maintain and test.

What is the Entity Object pattern?

It is a TypeScript implementation of the companion object pattern where an interface and a constant share the same name. This allows you to use the name as both a type for data and an object for domain logic functions.

Can I use these entity objects in React components?

Absolutely. This pattern is ideal for React as it allows components to call domain logic directly (e.g., AdGroup.canEdit(data)) rather than duplicating logic inside hooks or components.

Entity Object Pattern for TypeScript

Name: Entity Object Pattern for TypeScript
Author: seonghyeonkimm

byseonghyeonkimm

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Implements the companion object pattern to group domain logic and interfaces for cleaner, reusable TypeScript code.

This skill automates and guides the implementation of the Entity Object (Companion Object) pattern in TypeScript projects. By grouping domain logic functions within a constant object sharing the same name as an interface, it creates a single source of truth for business rules that can be shared across UI components, API services, and unit tests. It provides a structured, layered approach to categorizing logic—from basic state checks to complex composite behaviors—ensuring high cohesion and reducing logic duplication during the TDD refactoring phase.

主な機能

01Companion object pattern implementation with name-matched interfaces and constants

02Standardized naming conventions for domain functions including is*, get*, can*, and should*

03Systematic extraction of domain logic from TDD Given/When/Then scenarios

04Layered logic architecture (Base, Derived, and Composite layers) to prevent circular dependencies

050 GitHub stars

06Cross-layer reusability for UI rendering, API request building, and unit testing

ユースケース

01Synchronizing validation and business rules between frontend UI and backend services

02Refactoring scattered domain logic into reusable, testable entity objects during TDD

03Establishing a consistent pattern for Domain-Driven Design (DDD) in TypeScript projects

主な機能

01Companion object pattern implementation with name-matched interfaces and constants

02Standardized naming conventions for domain functions including is*, get*, can*, and should*

03Systematic extraction of domain logic from TDD Given/When/Then scenarios

04Layered logic architecture (Base, Derived, and Composite layers) to prevent circular dependencies

050 GitHub stars

06Cross-layer reusability for UI rendering, API request building, and unit testing

ユースケース

01Synchronizing validation and business rules between frontend UI and backend services

02Refactoring scattered domain logic into reusable, testable entity objects during TDD

03Establishing a consistent pattern for Domain-Driven Design (DDD) in TypeScript projects