code-refactoring-patterns

Code Refactoring Patterns

A comprehensive guide to refactoring code systematically while maintaining functionality and improving quality.

When to Refactor

• Code smells detected (duplicated code, long functions, etc.)
• Before adding new features to complex areas
• After understanding improves ("now I see a better way")
• When tests are in place
• Performance optimization needed

Refactoring Rules

1. Never refactor without tests: Write tests first if they don't exist
2. Small steps: Make one change at a time
3. Run tests after each change: Ensure nothing breaks
4. Commit often: Each working refactor is a commit
5. Don't mix refactoring with feature work: Separate concerns

Common Code Smells

1. Long Method/Function

Smell: Functions over 20-30 lines

Refactor: Extract Method

// Before
function processOrder(order: Order) {
  // Validate order (10 lines)
  // Calculate totals (15 lines)
  // Apply discounts (12 lines)
  // Send confirmation (8 lines)
}

// After
function processOrder(order: Order) {
  validateOrder(order);
  const totals = calculateTotals(order);
  const finalPrice = applyDiscounts(totals, order);
  sendConfirmation(order, finalPrice);
}

2. Duplicated Code

Smell: Same code in multiple places

Refactor: Extract Function/Class

// Before
function formatUserName(user: User) {
  return `${user.firstName} ${user.lastName}`;
}

function formatAuthorName(author: Author) {
  return `${author.firstName} ${author.lastName}`;
}

// After
function formatFullName(person: { firstName: string; lastName: string }) {
  return `${person.firstName} ${person.lastName}`;
}

3. Long Parameter List

Smell: Functions with 4+ parameters

Refactor: Parameter Object

// Before
function createUser(
  firstName: string,
  lastName: string,
  email: string,
  phone: string,
  address: string
) { }

// After
interface UserDetails {
  firstName: string;
  lastName: string;
  email: string;
  phone: string;
  address: string;
}

function createUser(details: UserDetails) { }