# Expert Code Refactoring > Expert code refactoring for Java, JavaScript, and React projects. Focuses on SOLID principles, design patterns, and idiomatic improvements while ensuring test stability. Use when this capability is needed. - Skill: `tomevault-io/expert-code-refactoring` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/expert-code-refactoring` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/expert-code-refactoring/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Web & Frontend - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/expert-code-refactoring --- # Refactoring Skill This skill guides the agent in refactoring codebases by identifying technical debt and applying industry-standard patterns tailored to the specific technology stack. ## General Refactoring Workflow 1. **Analyze Context:** Read the file and its associated tests. Identify dependencies and usage patterns. 2. **Verify Tests:** Before any changes, run existing tests to ensure a stable baseline. 3. **Identify Smells:** Look for long methods, deep nesting, duplicate code, or tight coupling. 4. **Incremental Changes:** Apply transformations in small, verifiable steps. 5. **Re-verify:** Run tests after each significant change. ## Architecture & Clean Code (Global) - **Naming:** Rename variables, functions, and classes to be descriptive and reveal intent. Avoid abbreviations. - **AHA Programming:** Avoid Hasty Abstractions. Only abstract code when the duplication is clear and the abstraction doesn't make the code harder to follow. - **Functions:** Keep functions small. Aim for a low number of parameters (prefer objects/records for many parameters). - **Cognitive Load:** Reduce nesting levels (aim for max 2-3 deep). Use early returns to keep the "happy path" aligned to the left. ## Refactoring for Testability - **Dependency Injection (DI):** Replace hardcoded instances or static calls with injected dependencies (via constructor or parameters). - **Interface Segregation:** If a class depends on a large interface but only uses one method, extract a smaller interface. - **Pure Functions:** Extract business logic into pure functions that don't depend on external state or side effects, making them trivial to unit test. - **Mocking Boundaries:** Identify "seams" where you can inject mocks (e.g., Database, Network, System Clock). ## Legacy Code Techniques (Safe Changes) - **Characterization Tests:** If tests are missing, write "Golden Master" tests that record the current behavior *before* changing it. - **Sprout Method:** When adding a feature to a messy method, write the new logic in a new, clean method and call it from the old one. - **Wrap Method:** Add new behavior by creating a new method with the same signature that calls the old method and then adds the new logic. - **Break Dependencies:** Use the "Extract and Override" pattern to isolate untestable static calls or constructors in a protected method that can be overridden in a test subclass. ## Common Code Smells & Solutions | Smell | Description | Refactoring Pattern | | :--- | :--- | :--- | | **Magic Literals** | Hardcoded numbers/strings. | **Extract Constant** or **Enum**. | | **Long Method** | Method does too many things. | **Extract Method**. | | **Large Class** | Too many responsibilities. | **Extract Class** or **Extract Interface**. | | **Feature Envy** | Method uses another object's data more. | **Move Method**. | | **Primitive Obsession** | Using primitives for domain concepts. | **Introduce Value Object**. | | **Multi‑File Change Requirement** | One change affects many files. | **Move Field** or **Inline Class** to centralize. | ## Language Specifics ### Java - **SOLID & Modern Features:** Use `record` (Java 14+), `sealed` classes (Java 17+), and **Switch Pattern Matching**. - **Streams & Optional:** Replace imperative loops with `Stream`. Use `Optional` to eliminate null checks. - **Immutability:** Use `final` and immutable collections (`List.of`, `Map.of`). - **Exception Handling:** Use try-with-resources. Avoid catching `Throwable` or `Exception` generically. ### JavaScript / TypeScript - **Modern Syntax:** `const` by default, destructuring, spread/rest, arrow functions. - **TypeScript Advanced:** **Discriminated Unions**, **Utility Types** (`Pick`, `Omit`), and **Custom Type Guards**. - **Data Integrity:** Use Zod or similar for runtime validation at API/IO boundaries. - **Async Patterns:** Prefer `Promise.all` for concurrency; avoid "async-await" inside loops where possible. ### React - **Component Design:** Decompose large components. Extract logic into **Custom Hooks**. - **State Management:** **Principle of Least Privilege** (keep state local). Avoid **Prop Drilling** with Context or Composition. - **Performance:** Use `useMemo`/`useCallback` for stable references. Avoid inline function definitions in props of memoized children. - **Testing:** Focus on user behavior and accessible roles (`getByRole`) via **React Testing Library**. ## Security & Reliability - **Input Validation:** Sanitize and validate all external input. - **Secrets:** Never hardcode keys; use environment variables. - **Dependencies:** Update deprecated/vulnerable packages discovered during refactoring. ## Constraints - Never change external APIs or public interfaces without explicit user permission. - Always maintain or improve test coverage. - Adhere to the project's existing linting and formatting rules. --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/grishaangelovgh) — claim your Tome and manage your conversions.