What the shelf is worth

easyinventoryTypeScript

Month-end valuation multiplies what is on each shelf by its unit cost and adds it up.

Quantity and cost are both in whole units; the answer is in minor currency units.
Negative quantities are counting errors — skip those rows entirely.
An empty shelf is worth nothing.

stockValue(rows: list<Row>) → int

Where you start

function stockValue(rows: Row[]): number {
  
}

Call	Result
`stockValue([{"qty":3,"unitCost":250},{"qty":2,"unitCost":100}])`	`950`
`stockValue([{"qty":-4,"unitCost":500},{"qty":1,"unitCost":500}])`	`500`
`stockValue([{"qty":0,"unitCost":900}])`	`0`
`stockValue([])`	`0`

One pass, one accumulator, one guard.

Reference solution in TypeScript

function stockValue(rows: Row[]): number {
  let total = 0;
  for (const r of rows) if (r.qty > 0) total += r.qty * r.unitCost;
  return total;
}