Group and Sum Array Items

groupAndSum.js

// Group and sum the value.
function groupAndSum(list) {
  const existingItems = {}
  list.forEach((item) => {
    if (!existingItems[item.name]) {
      existingItems[item.name] = item;
      return;
    }
    
    existingItems[item.name] = {
      ...existingItems[item.name],
      amount: item.amount + existingItems[item.name].amount,
    }
  });
  
  return Object.values(existingItems);
}


// Usage
var duplicatedItems = [
  {
    name: "a",
    amount: 1,
  },
  {
    name: "a",
    amount: 4,
  },
  {
    name: "b",
    amount: 2,
  },
];
groupAndSum(
  duplicatedItems
)