Refactoring

Refactoring: Improving the Design of Existing Code (2nd Edition, ISBN 0134757599) by Martin Fowler is a classic guide that teaches programmers how to improve the internal structure of existing code without changing its observable behavior. This updated edition adds modern examples (including JavaScript), expands the catalog of refactorings, and covers topics like code smells, core refactoring principles, test-driven development, modular design, restructuring conditional logic, data organization, API design, and addressing misuse of inheritance. Fowler emphasizes that refactoring should be a continuous part of the development process, carried out in small, verifiable steps to make code more understandable, flexible, and maintainable.