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 = [];
for (let i = 0; i < items.length; i++) {
    if (items[i].in_stock) 
        inStockItems.push(items[i]);
}

let total = 0;
for (let i = 0; i < inStockItems.length; i++) {
    total += inStockItems[i].price;
}

console.log(total);