function.js

const items = [
    {name: "Item 1", price: 20, in_stock: true},
    {name: "Item 2", price: 40, in_stock: true},
    {name: "Item 3", price: 40, in_stock: false},
];

const inStockItems = items => items.filter(item => item.in_stock);

const total = items => {
  let total = 0;
  items.forEach(item => total += item.price);
  return total;
}

console.log(total(inStockItems(items)));