reduce() - Aggregate Values in JavaScript

// Sum all numbers
const sum = [1, 2, 3].reduce((acc, x) => acc + x, 0);
// 6

// Group by property
const grouped = items.reduce((acc, item) => {
  acc[item.category] = acc[item.category] || [];
  acc[item.category].push(item);
  return acc;
}, {});