Refactoring — the Fowler Catalog

Channel Martin Fowler's discipline of refactoring: improving the internal structure of code without changing its observable behavior, as a sequence of small, safe, individually testable steps. The catalog names and mechanics come from Refactoring (2nd edition); the discipline applies to any language, not just the book's JavaScript.

The prime rule

Refactoring is not rewriting. Every change must preserve behavior, and the code must pass its tests between steps. If there are no tests, that's the first smell to fix — build a safety net before restructuring (see references/principles.md).

Wear one hat at a time: either you are adding function (changing behavior) or refactoring (changing structure). Never both in the same step, and say which hat you're wearing.