Nested JSON.

Theory. Real data is nested: an array of records, and each record has an array of parts. JSON carries it without trouble — stringify walks the depth itself. After parse you get the same structure back.

The work is in the walk: for (const item of data) for the outer array, and inside a second loop (or reduce) for the parts. Show the result as list items (createElement + appendChild) and a count.

Small examples:

const data = JSON.parse(raw.textContent); for (const item of data) { let sum = 0; for (const part of item.parts) sum += part.v; const li = document.createElement("li"); li.textContent = item.name + ": " + sum; list.appendChild(li); } count.textContent = String(data.length);

JSON.stringify(data[0]) shows only the first record with all its nesting.

Common mistake: forgetting that parts is an array; adding strings instead of numbers; not resetting the sum for each record.