Code Refactoring

Improve code quality without changing behavior.

When to Use

• Code is hard to understand or modify

• Duplicated logic across files

• Functions/classes are too large

• Technical debt reduction

• Before adding new features

Refactoring Process

• Ensure tests exist - Add tests before refactoring

• Small steps - Make incremental changes

• Run tests - Verify after each change

• Commit often - Keep changes reversible

Common Refactorings

Extract Function

// Before function processOrder(order) { // 50 lines of validation // 30 lines of calculation // 20 lines of notification }

// After function processOrder(order) { validateOrder(order); const total = calculateTotal(order); notifyCustomer(order, total); }

Replace Conditionals with Polymorphism

// Before function getPrice(type) { if (type === "regular") return basePrice; if (type === "premium") return basePrice * 1.5; if (type === "vip") return basePrice * 0.8; }

// After const pricingStrategies = { regular: (base) => base, premium: (base) => base * 1.5, vip: (base) => base * 0.8, }; const getPrice = (type) => pricingStrategiestype;

Remove Duplication

// Before function getUserName(user) { return user?.profile?.name ?? "Unknown"; } function getOrderName(order) { return order?.customer?.name ?? "Unknown"; }

// After const getName = (obj, path) => path.reduce((o, k) => o?.[k], obj) ?? "Unknown"; const getUserName = (user) => getName(user, ["profile", "name"]); const getOrderName = (order) => getName(order, ["customer", "name"]);

Code Smells

Smell Symptom Refactoring

Long Function

20 lines Extract Function

Large Class

200 lines Extract Class

Duplicate Code Same logic repeated Extract and reuse

Long Parameter

3 params Use object/builder

Feature Envy Uses other class's data Move method

Primitive Obsession Strings for everything Create value objects

Quality Metrics

• Cyclomatic Complexity - Keep under 10 per function

• Nesting Depth - Max 3 levels

• Function Length - Under 20 lines preferred

• File Length - Under 300 lines preferred

Safety Checklist

• Tests exist and pass

• No behavior changes intended

• Changes are incremental

• Each step is committed

• Code review requested

Examples

Input: "This function is too long" Action: Identify logical sections, extract into focused functions, verify tests pass

Input: "Reduce duplication in these files" Action: Find common patterns, extract shared utilities, update call sites