merge_basket.js

const online_basket = [
  { id: 1, quantity: 2 },
  { id: 3, quantity: 1 },
]

const offline_basket = [
  { id: 5, quantity: 1 },
  { id: 3, quantity: 2 },
  { id: 1, quantity: 1 }
]

function mergeBaskets(online, offline) {
  const mergedBasket = [...online];

  offline.forEach(offlineItem => {
    const existingItem = mergedBasket.find(item => item.id === offlineItem.id);
    
    if (existingItem) {
      if (offlineItem.quantity > existingItem.quantity) {
        existingItem.quantity = offlineItem.quantity;
      }
    } else {
      mergedBasket.push(offlineItem);
    }
  });

  return mergedBasket;
}

mergeBaskets(online_basket, offline_basket)