Refactoring Techniques

How it works

1. Input arrives
2. Core component processes
3. Result produced
4. Observe and iterate

Overview

Common refactorings include Extract Method, Rename, Introduce Parameter Object, and Replace Conditional with Polymorphism.

Learning Objectives

Real-World Examples

Code example

Replace Conditional with Polymorphism for shipping cost calculation:

// Before
function shippingCost(country: string, weightKg: number): number {
  if (country === 'US') return 5 + weightKg * 1;
  if (country === 'IN') return 3 + weightKg * 0.8;
  return 10 + weightKg * 1.2;
}

// After
interface ShippingRule { cost(weightKg: number): number }
class USRule implements ShippingRule { cost(w: number): number { return 5 + w * 1 } }
class INRule implements ShippingRule { cost(w: number): number { return 3 + w * 0.8 } }
class DefaultRule implements ShippingRule { cost(w: number): number { return 10 + w * 1.2 } }

var rules: Record<string, ShippingRule> = { US: new USRule(), IN: new INRule() };
function shippingCost2(country: string, weightKg: number): number {
  var rule = rules[country] || new DefaultRule();
  return rule.cost(weightKg);
}

Implementation Notes

Best Practices

Common Pitfalls