refactor-simplifying-conditionals

Refactor: Simplifying Conditional Expressions

Overview

These 8 techniques flatten, clarify, and eliminate conditional logic. Complex conditionals are a major source of bugs. Goal: make each branch's purpose obvious, eliminate duplication across branches, and replace type-switching with polymorphism.

When to Use

• Nested if/else deeper than 2 levels
• Same condition checked in multiple places
• Switch statements on type codes that grow with each new type
• Complex boolean expressions
• Null checks scattered throughout

Quick Reference

Technique	Problem	Solution
Decompose Conditional	Complex condition with big then/else blocks	Extract condition and branches into named methods
Consolidate Conditional	Multiple conditions with same result	Combine into single condition with descriptive name
Consolidate Duplicate Fragments	Same code in every branch	Move shared code outside the conditional
Remove Control Flag	Boolean controls loop flow	Use break, return, or continue
Guard Clauses	Deep nesting from special-case checks	Handle edge cases early with return
Replace Conditional with Polymorphism	Switch on type drives different behavior	Subclass or strategy per type
Introduce Null Object	Null checks repeated before using an object	Null/Default implementation that does nothing
Introduce Assertion	Code assumes a condition but doesn't check it	Explicit assertion to document and enforce

Techniques in Detail

1. Decompose Conditional

Before:

function calculateCharge(date: Date, quantity: number, plan: Plan): number {
  if (date.getMonth() >= 6 && date.getMonth() <= 8) {
    return quantity * plan.summerRate + plan.summerServiceCharge;
  } else {
    return quantity * plan.regularRate + plan.regularServiceCharge;
  }
}

After:

function calculateCharge(date: Date, quantity: number, plan: Plan): number {
  return isSummer(date) ? summerCharge(quantity, plan) : regularCharge(quantity, plan);
}

function isSummer(date: Date): boolean {
  return date.getMonth() >= 6 && date.getMonth() <= 8;
}

function summerCharge(quantity: number, plan: Plan): number {
  return quantity * plan.summerRate + plan.summerServiceCharge;
}

function regularCharge(quantity: number, plan: Plan): number {
  return quantity * plan.regularRate + plan.regularServiceCharge;
}