Any fool can write code that a computer can understand. Good programmers write code that humans can understand.

Fowler and Beck’s second edition of Refactoring is still the book I hand to engineers when we’re about to touch legacy code. The catalog of refactorings—Extract Function, Introduce Parameter Object, Replace Conditional with Polymorphism—gives you named moves with mechanics, motivations, and before/after examples you can translate to any language. Over the last year we’ve used it to modernize a decade-old Java service and a pile of TypeScript reducers; the step-by-step recipes paired with tests kept us shipping safely instead of rewriting from scratch. The newer chapters address lambdas, streams, and microservices, and the online catalog makes it easy to search for a particular smell mid-PR. If you refactor as part of your day job (and you should), this belongs on your desk.

Martin Fowler's systematic guide to refactoring code. Learn named refactoring moves with step-by-step mechanics to improve code design safely and effectively.

Refactoring: Improving the Design of Existing Code

Refactoring: Improving the Design of Existing Code (2nd Edition)

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Refactoring: Improving the Design of Existing Code (2nd Edition)