version: "1.0.0" name: refactoring description: > Code refactoring skill focused on safe, incremental transformations that preserve behavior. Covers extract method, rename, introduce parameter, replace conditional with polymorphism, and other Fowler refactoring patterns. license: MIT

Refactoring Skill — Safe Code Transformations

This skill provides systematic refactoring guidance ensuring behavior preservation.

Core Principle

Refactoring changes the STRUCTURE without changing the BEHAVIOR.

If behavior needs to change, that's a feature — do it separately.

Refactoring Catalog

Extract Method

// BEFORE
function printOwing(invoice) {
  // Print banner
  console.log('*******************');
  console.log('*** Customer Owes ***');
  console.log('*******************');
  // Calculate outstanding
  let outstanding = 0;
  for (const o of invoice.orders) {
    outstanding += o.amount;
  }
  // Print details
  console.log(`name: ${invoice.customer}`);
  console.log(`amount: ${outstanding}`);
}
// AFTER
function printOwing(invoice: Invoice): void {
  printBanner();
  const outstanding = calculateOutstanding(invoice.orders);
  printDetails(invoice.customer, outstanding);
}

Replace Conditional with Polymorphism

// BEFORE
function getDiscount(customerType: string): number {
  if (customerType === 'premium') return 0.2;
  if (customerType === 'gold') return 0.15;
  if (customerType === 'silver') return 0.1;
  return 0;
}
// AFTER
abstract class Customer {
  abstract getDiscount(): number;
}
class PremiumCustomer extends Customer {
  getDiscount(): number {
    return 0.2;
  }
}
class GoldCustomer extends Customer {
  getDiscount(): number {
    return 0.15;
  }
}

Introduce Parameter Object

// BEFORE
function createReport(
  title: string,
  startDate: Date,
  endDate: Date,
  format: string,
  includeCharts: boolean,
  groupBy: string
) { ... }
// AFTER
interface ReportOptions {
  title: string;
  dateRange: { start: Date; end: Date };
  format: 'pdf' | 'html' | 'csv';
  includeCharts: boolean;
  groupBy: 'day' | 'week' | 'month';
}
function createReport(options: ReportOptions) { ... }

Safe Refactoring Protocol

1. GREEN: Ensure all tests pass before starting
2. SMALL: Make one refactoring at a time
3. TEST: Run tests after EACH refactoring step
4. COMMIT: Commit after each successful refactoring
5. REVIEW: Code review the refactoring separately

Refactoring Checklist

Before refactoring:

• [ ] All existing tests pass
• [ ] Test coverage is adequate for the code being refactored
• [ ] No feature work mixed in
• [ ] Rollback plan exists (git commit before starting)

During refactoring:

• [ ] One transformation at a time
• [ ] Tests run after each step
• [ ] No behavior changes
• [ ] No dead code left behind

After refactoring:

• [ ] All tests still pass
• [ ] No new lint warnings
• [ ] Code is cleaner than before
• [ ] No functionality lost

Forbidden Actions

• NEVER mix refactoring with feature changes
• NEVER refactor without passing tests first
• NEVER skip running tests between steps
• NEVER leave dead code after refactoring
• NEVER change behavior during refactoring

When NOT to Use

Do NOT use this skill when:

• Writing new application logic (use domain-driven skill)
• Designing database schemas (use database-design skill)
• Writing API endpoint implementations (use api-design skill)
• Reviewing code for security issues (use code-review skill)
• Performing security audits (use security-auditor skill)
• Writing SQL queries (use sql-best-practices skill)
• Designing multi-page website layouts (use design-system skill)
• Reviewing git workflows (use git-workflow skill)