Replace Nested Conditional with Guard Clauses

Removes smells

Symptom

Functions with deeply nested if/else where the happy path is buried inside multiple levels of indentation, and edge cases are conditionals around the main flow.

Goal

Edge cases bail out early at the top of the function; the main flow is unindented and tells the happy path linearly.

Before the refactoring

function payAmount(employee) {
  if (employee.isSeparated) {
    return separationPay(employee);
  } else {
    if (employee.isRetired) {
      return retirementPay(employee);
    } else {
      return regularPay(employee);
    }
  }
}

After the refactoring

function payAmount(employee) {
  if (employee.isSeparated) return separationPay(employee);
  if (employee.isRetired)   return retirementPay(employee);
  return regularPay(employee);
}

Example source: Illustrative example written for this site, not a quotation from any source.

Pressure

The dominant case is hidden under indentation; readers must trace down through edge-case branches to find the main flow; new edge cases extend an already-tangled structure.

Tradeoff

If multiple paths share work, premature returns can duplicate that work — extract first, then guard.

Relief

Indentation drops; the dominant case is obvious; new edge cases land at the top without disturbing the rest.

Trap

Inlining guard clauses for every condition — including ones where the edge case shares work with the main path; the early returns duplicate work the structure was sharing.