lastDemo.js

Array.prototype.last = function(propertySelector = obj => obj) {
  const filtered = this.filter(propertySelector);
  return filtered[filtered.length - 1];
};

function lastDemo(orders) {
  const lastOrderAfterMarch = orders.last(order => order.orderDate >= march);
  printHeaderFooter(
    "Last order after March",
    () => printOrder(lastOrderAfterMarch, indentBy),
    indentBy
  );

  const lastOrderAfterSeptember =
    orders.last(order => order.orderDate >= september) || null;
  printHeaderFooter(
    "Last or Default order after September",
    () => printOrder(lastOrderAfterSeptember, indentBy),
    indentBy
  );
}