Refactoring Legacy Code with React Best Practices: Before and After

Refactoring Legacy Code with React Best Practices: Before and After A practical case study: How to transform a messy React project into a maintainable codebase Project Background Original Codebase State Project Scale : 5,000+ lines of code Tech Stack : React 15 + Redux + jQuery Maintenance Cost : Every change affects multiple components Team Situation : New members need 2 weeks to onboard Pain Point Analysis Code Quality Issues Components nested too deeply (deepest: 8 levels) Chaotic state management (Redux mixed with component state) Lack of type checking (all JavaScript) Disorganized styles (CSS-in-JS + traditional CSS) Performance Issues Component re-rendering No code splitting Large bundle size (2MB+) Refactoring Strategy 🎯 Goal Setting Short-term Goals (1 month) Implement code splitting Establish type system Optimize core components Long-term Goals (3 months) Complete migration to React 18 Establish test coverage Implement CI/CD 🔧 Technology Selection Core Upgrades React 15 → Reac