reduce() - Aggregate Values in JavaScript
From the JavaScript Array Methods cheat sheet · Transformation Methods · verified Jul 2026
reduce() - Aggregate Values
Reduce array to single value using accumulator
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;
}, {});🔴 Advanced - Powerful but complex method
💡 Can return any type: number, string, object, array
⚡ Use for sums, counts, grouping, flattening
⚠️ Always provide initial value to avoid errors
📌 Accumulator carries value between iterations