distinctDemos.js

function distinctDemo1(orders) {
  const distinctQuantityOrders = orders
    .map(order => order.quantity)
    .filter((quantity, index, self) => self.indexOf(quantity) === index);

  distinctQuantityOrders.forEach(quantity =>
    WriteLine(`Distinct Quantity: ${quantity}`)
  );
}

/**
 *  An alternate method of implementing Distinct() LINQ method using new "Set" introduced in ES6 and the spread operator
 */
function distinctDemo2(orders) {
  const distinctQuantityOrders = [
    ...new Set(orders.map(order => order.quantity))
  ];
  distinctQuantityOrders.forEach(quantity =>
    WriteLine(`Distinct Quantity: ${quantity}`)
  );
}