code-refactoring

Code Refactoring

Refactoring Principles

When to Refactor

• Before adding new features (make change easy, then make easy change)
• After getting tests passing (red-green-refactor)
• When you see code smells
• During code review feedback

When NOT to Refactor

• Without tests covering the code
• Under tight deadlines with no safety net
• Code that will be replaced soon
• When you don't understand what the code does

Common Code Smells

Long Methods

// BEFORE: Method doing too much
function processOrder(order: Order) {
  // 100 lines of validation, calculation, notification, logging...
}

// AFTER: Extract into focused methods
function processOrder(order: Order) {
  validateOrder(order);
  const total = calculateTotal(order);
  saveOrder(order, total);
  notifyCustomer(order);
}

Deeply Nested Conditionals

// BEFORE: Arrow code
function getDiscount(user: User, order: Order) {
  if (user) {
    if (user.isPremium) {
      if (order.total > 100) {
        if (order.items.length > 5) {
          return 0.2;
        }
      }
    }
  }
  return 0;
}

// AFTER: Early returns (guard clauses)
function getDiscount(user: User, order: Order) {
  if (!user) return 0;
  if (!user.isPremium) return 0;
  if (order.total <= 100) return 0;
  if (order.items.length <= 5) return 0;
  return 0.2;
}

Primitive Obsession

// BEFORE: Primitives everywhere
function createUser(name: string, email: string, phone: string) {
  if (!email.includes('@')) throw new Error('Invalid email');
  // more validation...
}

// AFTER: Value objects
class Email {
  constructor(private value: string) {
    if (!value.includes('@')) throw new Error('Invalid email');
  }
  toString() { return this.value; }
}

function createUser(name: string, email: Email, phone: Phone) {
  // Email is already validated
}

Feature Envy

// BEFORE: Method uses another object's data extensively
function calculateShipping(order: Order) {
  const address = order.customer.address;
  const weight = order.items.reduce((sum, i) => sum + i.weight, 0);
  const distance = calculateDistance(address.zip);
  return weight * distance * 0.01;
}

// AFTER: Move method to where the data is
class Order {
  calculateShipping() {
    return this.totalWeight * this.customer.shippingDistance * 0.01;
  }
}