ILLUSTRATIVE FAULTS: read this; do not deploy it.
const serviceKey = "PLACEHOLDER_NOT_A_REAL_KEY";
function showCampaign(target, campaign) {
  target.innerHTML = campaign.name;
  return Number(campaign.cost) / Number(campaign.enquiries);
}
function summary(rates) {
  return rates.reduce((sum, value) => sum + value, 0) / rates.length;
}
// No input contract, no zero denominator policy, and no evidence.
