refactoring-specialist

SKILL.md

Refactoring Specialist

Expert guidance on refactoring code to improve structure, readability, and maintainability while preserving functionality.

When This Skill Activates

Activates when you:

Ask to refactor code

Request cleanup or improvement

Mention "technical debt" or "code smell"

Want to improve code quality

Refactoring Principles

Preserve Behavior: Refactoring must not change external behavior

Small Steps: Make small, incremental changes

Test Coverage: Ensure tests pass before and after

Commit Often: Commit after each successful refactoring

Code Smells to Address

1. Long Method

Symptom: Function > 20-30 lines

Refactoring: Extract Method

// Before:
function processOrder(order) {
  // 50 lines of code
}

// After:
function processOrder(order) {
  validateOrder(order);
  calculateTotals(order);
  saveOrder(order);
  sendConfirmation(order);
}

2. Duplicate Code

Symptom: Similar code in multiple places

Refactoring: Extract Method / Template Method

// Before:
class UserService {
  async validateEmail(email) {
    if (!email || !email.includes('@')) return false;
    const domain = email.split('@')[1];
    return domain.length > 0;
  }
}
class AdminService {
  async validateEmail(email) {
    if (!email || !email.includes('@')) return false;
    const domain = email.split('@')[1];
    return domain.length > 0;
  }
}

// After:
class EmailValidator {
  async validate(email) {
    if (!email || !email.includes('@')) return false;
    return email.split('@')[1].length > 0;
  }
}

3. Large Class

Symptom: Class doing too many things

Refactoring: Extract Class

// Before:
class User {
  // Authentication
  // Profile management
  // Notifications
  // Reporting
}

// After:
class User { /* Core user data */ }
class UserAuth { /* Authentication */ }
class UserProfile { /* Profile management */ }
class UserNotifier { /* Notifications */ }

4. Long Parameter List

Symptom: Function with 4+ parameters

Refactoring: Introduce Parameter Object

// Before:
function createUser(name, email, age, address, phone, role) { ... }

// After:
function createUser(user: UserData) { ... }

interface UserData {
  name: string;
  email: string;
  age: number;
  address: string;
  phone: string;
  role: string;
}

5. Feature Envy

Symptom: Method uses more data from other classes

Refactoring: Move Method

// Before:
class Report {
  formatSummary(formatter) {
    const options = formatter.getFormattingOptions();
    // ...
  }
}

// After:
class Formatter {
  formatReport(report) {
    const discount = this.discountLevel;
    // ...
  }
}

6. Data Clumps

Symptom: Same data appearing together

Refactoring: Extract Value Object

// Before:
function drawShape(x, y, width, height) { ... }
function moveShape(x, y, width, height, dx, dy) { ... }

// After:
class Rectangle {
  constructor(x, y, width, height) { ... }
}
function drawShape(rect: Rectangle) { ... }

7. Primitive Obsession

Symptom: Using primitives instead of small objects

Refactoring: Replace Primitive with Object

// Before:
function createUser(name, email, phone) { ... }

// After:
class Email {
  constructor(value) {
    if (!this.isValid(value)) throw new Error('Invalid email');
    this.value = value;
  }
  // ...
}

8. Switch Statements

Symptom: Large switch on type

Refactoring: Replace Conditional with Polymorphism

// Before:
function calculatePay(employee) {
  switch (employee.type) {
    case 'engineer': return employee.salary * 1.2;
    case 'manager': return employee.salary * 1.5;
    case 'sales': return employee.salary * 1.1;
  }
}

// After:
interface Employee {
  calculatePay(): number;
}
class Engineer implements Employee {
  calculatePay() { return this.salary * 1.2; }
}

9. Temporary Field

Symptom: Variables only used in certain scenarios

Refactoring: Extract Class

// Before:
class User {
  calculateRefund() {
    this.tempRefundAmount = 0;
    // complex calculation
    return this.tempRefundAmount;
  }
}

// After:
class RefundCalculator {
  calculate(user) {
    // ...
  }
}

10. Comments

Symptom: Code needs extensive comments

Refactoring: Extract Method with clear name

// Before:
// Calculate the total price including discounts
// and tax based on user location
function calc(u, i) {
  let t = 0;
  // discount logic
  if (u.vip) t *= 0.9;
  // tax logic
  if (u.state === 'CA') t *= 1.08;
  return t;
}

// After:
function calculateTotalPrice(user: User, items: Item[]): number {
  let total = items.sum(i => i.price);
  if (user.isVIP) {
    total = applyVIPDiscount(total);
  }
  return applyTax(total, user.state);
}

Refactoring Steps

Identify the smell - What makes this code hard to work with?

Determine the refactoring - Which technique applies?

Ensure tests pass - Green before starting

Apply the refactoring - Make the change

Run tests - Verify behavior unchanged

Commit - Small, atomic commits

Safe Refactoring Practices

Use your IDE's refactoring tools (Rename, Extract, Move)

Run tests frequently (after each change)

Keep commits small and focused

Write a descriptive commit message

Consider code reviews for complex refactorings

Before Refactoring

 Tests are passing

 I understand what the code does

 I have identified the specific code smell

 I know which refactoring to apply

 I have a rollback plan

After Refactoring

 Tests still pass

 Code is more readable

 Code is easier to maintain

 No new code smells introduced

 Documentation updated if needed

References

references/smells.md - Complete code smell catalog

references/techniques.md - Refactoring techniques

references/checklist.md - Refactoring checklist