Custom Sort - on a column in a table so that blank values always at the bottom - not working. Order is 'asc' but actual sort is 'desc'

[smefocus]

Using List.js v 2.3.1

I am sorting a column in a table. Column has some blank values. My aim is to sort ONLY non-blank values, and the blank values must always come AFTER non-blank values.

Here's the Custom Sort JavaScript function:

function customSort(a, b, options) {
    let valA = a.values()[options.valueName];
    let valB = b.values()[options.valueName];

    let isBlankA = (valA === '');
    let isBlankB = (valB === '');

    if (isBlankA && isBlankB) {
        return 0;
    } else if (isBlankA) {
        return 1;
    } else if (isBlankB) {
        return -1;
    } else {
        if (valA === valB) {
            return 0;
        }
        if (options.order === 'asc') {
            return valA < valB ? -1 : 1;
        }
        else {
            return valA < valB ? 1 : -1;
        }
        return 0;
    }
}

And here's how I am calling it:
sortMapList.sort(colName, { order: sortDir, sortFunction: customSort });

When I send sortDir = 'asc' the column gets sorted in 'desc' order! and vice-versa

Even if I remove the following code

        if (options.order === 'asc') {
            return valA < valB ? -1 : 1;
        }
        else {
            return valA < valB ? 1 : -1;
        }

and replace it with a single line (assuming the order is taken care of by list.js)

return valA < valB ? -1 : 1;

nothing changes.

The Blank data in the column is at the top when in 'asc' order and at the bottom when in 'desc' order.