ScriptdrillTotals per customer
A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.
The task
Each order looks like `{ customer, items: [{ price, qty }] }`. Return an object mapping each customer to the total of all their orders, where an item is worth `price * qty`. A customer whose orders have no items still appears, with 0. Prices can be negative (a discount line).
What this exercise teaches
The inner reduce with a 0 start value turns an empty item list into 0, and `(totals[c] || 0) + subtotal` creates or extends the customer's total, so every customer appears exactly once.
A hint if you get stuck
Loop over the orders. For each one, `reduce` its items into a subtotal starting from `0`, then add it to `totals[order.customer]`, which starts at `0` too.
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