How can a sorted javascript array return incorrect values from the comparator?

Question

Say I have a list of items, which are sorted using a given comparator. I would expect that after sorting into ascending order comparator(element[1], element[1+n]) should return -1 for all values of n> 1, because according to that comparator, element[1]

I am performing a custom sort and finding that after sorting there are instances where comparator(element[1], element[1+n]) returns 1. When I look at the instance I see that the comparator giving the correct output, i.e. element[1]>element[1+n]. I don't understand how this could be the case after performing a sort with that comparator.

If anyone has any idea of sort subtleties that I might have missed, I'd really appreciate their thoughts. Also, if I can provide more information that might shed light please let me know.

edit I thought this might be a more general question, but in response to mplungjan have added the custom sorter below. The sort is for a hierarchical dataset in the form of a flat list of objects. Each object has an id which might be as follows: 0 for root 1. 0-0 for its first child. 0-1 for its second child. etc.

Each object in the list had a field 'parent' which has the id of its parent. Essentially data.sort isn't doing what I think it should be.

function CurrencyTreeSorter(a, b) {

    a_id = a.id.split("-");
    b_id = b.id.split("-"); 

    if(a_id.length != b_id.length || a_id.slice(0, a_id.length-1).toString() != b_id.slice(0, b_id.length-1).toString()){
        var i = 0;
        while (i < a_id.length && i < b_id.length && a_id[i] == b_id[i]) {
            i++;
            }

        if (i == a_id.length || i == b_id.length){
            return a_id.length > b_id.length ? 1 : -1;
        }
        else{   
            while (a.level > i) {
                a = getParent(dataMap, a);
            }

            while (b.level > i) {
                b = getParent(dataMap, b);
            }
        }
    }

    var x, y;
    if (a[sortcol] == "-") {
        x = -1;
    }
    else {
        x = parseFloat(a[sortcol].replace(/[,\$£€]/g, ""));
    }

    if (b[sortcol] == "-") {
        y = -1;
    }
    else {
        y = parseFloat(b[sortcol].replace(/[,\$£€]/g, ""));
    }

    return sortdir * (x == y ? 0 : (x > y ? 1 : -1));

}

Answer 1

This turned out to be an issue with Chrome, described here and here. Essentially it's not safe to return zero from the comparator/comparer.