Intro & Principles
What refactoring is, why and when, small steps backed by tests, and reading code smells. Start →
Refactoring — From Zero to Hero
A standalone, beginner→advanced course on refactoring — improving the internal structure of code without changing what it does. Learn the discipline (small steps backed by tests), spot code smells, and apply a catalog of refactorings — each with a before→after in TypeScript, Python, Go, and Rust.
What you’ll learn
Section titled “What you’ll learn”Composing Methods
Extract & Inline Function, Extract Variable, Replace Temp with Query, Split Phase. Compose →
Moving Features
Move Function & Field, Extract & Inline Class, Hide Delegate / Remove Middle Man. Move →
Organizing Data
Encapsulate Variable & Collection, Replace Magic Literal, Replace Primitive with Object. Organize →
Simplifying Conditionals
Decompose & Consolidate, Guard Clauses, Replace Conditional with Polymorphism, Null Object. Clarify →
Simplifying APIs
Rename, Parameterize, Introduce Parameter Object, Remove Flag Argument, Factory. Refine →
Generalization & Inheritance
Pull Up / Push Down, Extract Superclass & Interface, Replace Inheritance with Delegation. Generalize →
How this course works
Section titled “How this course works”Before → After, four languages
Every refactoring shows the messy code and its improved form in TypeScript, Python, Go, and Rust — synced tabs, so pick your language once.
Driven by smells
Each refactoring starts from the code smell it cures, so you know exactly when to reach for it.
Safe, small steps
The mechanics break each change into tiny, behavior-preserving steps you run tests between — refactoring without fear.
Bilingual + read mode
English and ไทย, quizzes with saved progress, and a distraction-free read mode.