reduce.js

const lineItems = [
  { name: 'Carmenere', price: 35, quantity: 2 },
  { name: 'Cabernet', price: 50, quantity: 1 },
  { name: 'Merlot', price: 98, quantity: 10 },
];

const totalLine = line =>
  line.quantity * line.price;

const sumTotal = lines =>
  lines.reduce((total, line) => total += totalLine(line), 0);

console.log(sumTotal(lineItems));