Default comparison used for sorting does not handle undefined values

[piotr-dobrogost]

Array.prototype.sort() has the following guarantee:

If compareFunction is not supplied, (…) All undefined elements are sorted to the end of the array.

For example:

> ['c', null, null, 'a', undefined, 'b'].sort()
< (6) ["a", "b", "c", null, null, undefined]

However, default comparison function used by the library – defaultCompare – does not make this guarantee:

> cmp = function (a, b) {
    if (a === b) return 0;
    return a > b ? 1 : -1;
}
> ['c', null, null, 'a', undefined, 'b'].sort(cmp)
< (6) ["a", "b", null, null, "c", undefined]

which is unfortunate as it makes default sorting broken in case of any undefined values. The fix should be easy: change current

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

to

    if (x === y) return 0;
    if ((x == null) && (y != null)) return 1;
    if ((x != null) && (y == null)) return -1;
    return x > y ? 1 : -1;

which gives:

> ['c', null, null, 'a', undefined, 'b'].sort(cmp)
< (6) ["a", "b", "c", null, null, undefined]

[alalonde]

See my comment in #60 .

[piotr-dobrogost]

@alalonde

I can not image that anyone would be negatively surprised that sorting ['c', null, null, 'a', undefined, 'b'] he would now get sorted sequence ["a", "b", "c", null, null, undefined] instead of random mess ["a", "b", null, null, "c", undefined] they have been getting earlier. All who wanted to handle undefined values must have already used custom comparator and for all others the behavior would be clearly better. Could you please reconsider merging this fix?