Computing the subtotal of all items on their property criteria: qty * price
You are computing the sum of an array, with a twist. Use Array.reduce() to compute sums.

Furthermore, if you are going to use the ECMAScript let language feature, you should also use arrow function notation.

function subtotal(items) {
    return items.reduce(
        ((total, item) =&gt; total + item.qty * item.price),
        0.00
    );
}


Better naming would help. "Get" implies that you are retrieving something that already exists, which is not the case here.  Also, i has a connotation of being an index counter, which makes its use in your forEach() confusing.