countDemo.js

Array.prototype.count = function(predicate = obj => true) {
  return this.filter(predicate).length;
};

function countDemo(orders) {
  const march = new Date(2018, 3, 1);
  const ordersOnAndAfterMarch = orders.filter(
    order => order.orderDate >= march
  );
  printOrders(ordersOnAndAfterMarch, (indentBy = 4));
  const orderCountPlacedOnAndAfterMarch = orders.count(
    order => order.orderDate >= march
  );
  WriteLine(
    `Total Orders Placed On and After March: ${orderCountPlacedOnAndAfterMarch}`
  );
}