merge object & sum a single property javascript

Question

i have an array like this

[
  {
    item_guid: \"57e7a1cd6a3f3669dc03db58\"
    quantity:3
  },
  {
    item_guid: \"57e77b06e0566d496b51fed5\"
    quantity:         


        

Answer 1

var groupedItems = [];

var totalItems = [{item_guid: "57e7a1cd6a3f3669dc03db58", quantity:3},{item_guid: "57e77b06e0566d496b51fed5",quantity:3}, { item_guid: "57e7a1cd6a3f3669dc03db58", quantity:3 }, { item_guid: "57e77b06e0566d496b51fed5", quantity:3}];

totalItems.forEach((e) => {
  if (groupedItems.findIndex(x => x.item_guid === e.item_guid) < 0) {
    let totalQuantity = totalItems
                       .filter(x => x.item_guid === e.item_guid)
                       .map(x => x.quantity)
                       .reduce(function(a, b) { return a + b;});

    groupedItems.push({item_guid: e.item_guid, quantity: totalQuantity})
  }
})

console.log(groupedItems);