On page 27 of your "Jump Start Node.js" book, in the chapter02/lib/exchange.js excerpt- please explain the purpose of a BinaryHeap scoreFunction (in red below) that simply returns the argument you send it (basically, a no-op)?

Code:
function createBinaryHeap(orderType) {
    return new BinaryHeap(function(x) { return x; }, orderType);
}