Duplicated Code

Extract Function Slide Statements Pull Up Method

Symptom

The same code structure appears in two or more places — same shape with cosmetic variations, or copy-paste-modify patterns that drift over time.

Goal

One canonical home per behavior, with parameters for the variations.

Smellier version

function totalUSD(items) {
  return items.reduce((s, i) => s + i.price * i.qty, 0);
}
function totalEUR(items) {
  return items.reduce((s, i) => s + i.price * i.qty, 0);
}

Fresher version

function lineTotal(items) {
  return items.reduce((s, i) => s + i.price * i.qty, 0);
}

Savings

A bug fix or enhancement lands once, not in every clone — and the unifying name reveals shared intent.

Note

Bugs need to be fixed in every copy; behavior diverges as copies age, multiplying maintenance cost.