Accumulate.

Fourth class. From a list we build a sum and an average — budget classics.

function sumAmounts(list) { let total = 0; for (const n of list) total += n; return total; }

function averageAmount(list) { if (list.length === 0) return 0; return sumAmounts(list) / list.length; }

Empty list: average is 0 (avoid dividing by zero).

Common mistake: forgetting [] → 0; or computing total without return.