Replace Nested Conditional with Guard Clauses

Deep nesting hides the main logic. Guard clauses handle special/edge cases early and return immediately, leaving the happy path flat and prominent.

When to Use

• Method has a deeply nested if/else if/else chain
• One branch is the normal case; others are exceptions or edge cases
• Readers must scroll through guards to find core logic
• Cyclomatic complexity is high

How to Apply

1. Identify exceptional conditions (null, invalid state, permissions)
2. For each: add an early return (or throw) at the top of the method
3. Remove the now-redundant outer else
4. Flatten the remaining code
5. Run tests

Example

// Before
function getPayAmount(employee: Employee): number {
  if (employee.isSeparated) {
    return 0;
  } else {
    if (employee.isRetired) {
      return retiredAmount(employee);
    } else {
      return normalPayAmount(employee);
    }
  }
}

// After
function getPayAmount(employee: Employee): number {
  if (employee.isSeparated) return 0;
  if (employee.isRetired) return retiredAmount(employee);
  return normalPayAmount(employee);
}

References

• refactoring.guru/replace-nested-conditional-with-guard-clauses