Agent Skills: React Refactor Best Practices

React Refactor Best Practices

Architectural refactoring guide for React applications. Contains 40 rules across 7 categories, prioritized by impact from critical (component and state architecture) to incremental (refactoring safety).

When to Apply

• Refactoring existing React codebases or planning large-scale restructuring
• Reviewing PRs for architectural issues and code smells
• Decomposing oversized components into focused units
• Extracting reusable hooks from component logic
• Improving testability of React code
• Reducing coupling between feature modules

Rule Categories

| Category | Impact | Rules | Key Topics | |----------|--------|-------|------------| | Component Architecture | CRITICAL | 8 | Compound components, headless pattern, composition over props, client boundaries | | State Architecture | CRITICAL | 7 | Colocation, state machines, URL state, derived values | | Hook Patterns | HIGH | 6 | Single responsibility, naming, dependency stability, composition | | Component Decomposition | HIGH | 6 | Scroll test, extraction by change reason, view/logic separation | | Coupling & Cohesion | MEDIUM | 4 | Dependency injection, circular deps, stable imports, barrel-free | | Data & Side Effects | MEDIUM | 4 | Server-first fetch, TanStack Query, error boundaries | | Refactoring Safety | LOW-MEDIUM | 5 | Characterization tests, behavior testing, integration tests |

Quick Reference

Critical patterns — get these right first:

• Use compound components instead of props explosion
• Colocate state with the components that use it
• Use state machines for complex UI workflows
• Separate container logic from presentational components

Common mistakes — avoid these anti-patterns:

• Lifting state to App when only one component reads it
• Using context for rapidly-changing values
• Monolithic hooks that fetch + transform + cache
• Testing implementation details instead of behavior

Table of Contents

1. Component Architecture — CRITICAL
   • 1.1 Apply Interface Segregation to Component Props — CRITICAL (prevents 30-50% of unnecessary re-renders)
   • 1.2 Colocate Files by Feature Instead of Type — CRITICAL (reduces cross-directory navigation by 70%)
   • 1.3 Convert Render Props to Custom Hooks — CRITICAL (eliminates 2-4 levels of nesting)
   • 1.4 Extract Headless Components for Logic Reuse — CRITICAL (5x more reuse scenarios)
   • 1.5 Prefer Composition Over Props Explosion — CRITICAL (reduces prop count by 50-70%)
   • 1.6 Separate Container Logic from Presentational Components — CRITICAL (enables independent testing)
   • 1.7 Use Compound Components for Implicit State Sharing — CRITICAL (reduces API surface by 60%)
   • 1.8 Push Client Boundaries to Leaf Components — HIGH (keeps 60-80% server-rendered)
2. State Architecture — CRITICAL
   • 2.1 Colocate State with Components That Use It — CRITICAL (reduces prop passing by 60%)
   • 2.2 Derive Values Instead of Syncing State — CRITICAL (eliminates double-render cycle)
   • 2.3 Lift State Only When Multiple Components Read It — CRITICAL (eliminates unnecessary parent re-renders)
   • 2.4 Use Context for Rarely-Changing Values Only — CRITICAL (5-50x fewer re-renders)
   • 2.5 Use State Machines for Complex UI Workflows — CRITICAL (reduces valid states from 2^n to N)
   • 2.6 Use URL Parameters as State for Shareable Views — CRITICAL (enables deep linking and sharing)
   • 2.7 Use useReducer for Multi-Field State Transitions — CRITICAL (eliminates impossible states)
3. Hook Patterns — HIGH
   • 3.1 Avoid Object and Array Dependencies in Custom Hooks — HIGH (prevents effect re-execution every render)
   • 3.2 Compose Hooks Instead of Nesting Them — HIGH (flattens dependency graph)
   • 3.3 Extract Logic into Custom Hooks When Behavior Is Nameable — HIGH (40-60% shorter components)
   • 3.4 Follow Hook Naming Conventions for Discoverability — HIGH (reduces navigation time by 40%)
   • 3.5 Keep Custom Hooks to a Single Responsibility — HIGH (3x easier to test)
   • 3.6 Stabilize Hook Dependencies with Refs and Callbacks — HIGH (prevents infinite loops)
4. Component Decomposition — HIGH
   • 4.1 Apply the Scroll Test to Identify Oversized Components — HIGH (3x faster code review)
   • 4.2 Complete Component Extraction Without Half-Measures — HIGH (enables independent testing and reuse)
   • 4.3 Extract Components by Independent Change Reasons — HIGH (70% fewer files touched per change)
   • 4.4 Extract Pure Functions from Component Bodies — HIGH (10x faster unit tests)
   • 4.5 Inline Premature Abstractions Before Re-Extracting — HIGH (40-60% simpler code)
   • 4.6 Separate View Layer from Business Logic — HIGH (5x faster test suite)
5. Coupling & Cohesion — MEDIUM
   • 5.1 Break Circular Dependencies with Intermediate Modules — MEDIUM (eliminates undefined-at-import-time bugs)
   • 5.2 Import from Stable Public API Surfaces Only — MEDIUM (enables internal refactoring)
   • 5.3 Use Barrel-Free Feature Modules for Clean Dependencies — MEDIUM (200-800ms build reduction)
   • 5.4 Use Dependency Injection for External Services — MEDIUM (3x faster test setup)
6. Data & Side Effects — MEDIUM
   • 6.1 Fetch Data on the Server by Default — MEDIUM (reduces client JS by 30-60%)
   • 6.2 Place Error Boundaries at Data Fetch Granularity — MEDIUM (errors isolated to affected section)
   • 6.3 Use Context Module Pattern for Action Colocation — MEDIUM (centralizes data mutations)
   • 6.4 Use TanStack Query for Client-Side Server State — MEDIUM (eliminates 80% of fetch boilerplate)
7. Refactoring Safety — LOW-MEDIUM
   • 7.1 Avoid Snapshot Tests for Refactored Components — LOW-MEDIUM (eliminates false test failures)
   • 7.2 Extract Pure Functions to Increase Testability — LOW-MEDIUM (10x faster test execution)
   • 7.3 Prefer Integration Tests for Component Verification — LOW-MEDIUM (catches 40% more bugs)
   • 7.4 Test Component Behavior Not Implementation Details — LOW-MEDIUM (5x fewer test updates)
   • 7.5 Write Characterization Tests Before Refactoring — LOW-MEDIUM (catches 90% of unintended changes)

References

1. https://react.dev
2. https://react.dev/learn/thinking-in-react
3. https://kentcdodds.com/blog/application-state-management-with-react
4. https://testing-library.com/docs/guiding-principles
5. https://patterns.dev

Related Skills

• For React 19 API best practices, see react skill
• For application performance optimization, see react-optimise skill
• For client-side form handling, see react-hook-form skill