Thanks for your solution, upvoted (clever +1)

countourMode = countTourMode, it should be :)

Just think about 1000 bottles of whine.

LOL. I suppose the King can store them in the palace cellar along with his 50 barrels of grizzle, 20 tubs of whinge, and that giant vat of moan that nobody wants to go near...

:-)

The ECMAScript standard doesn't specify and V8 (NodeJS, Chromium) doesn't guarantee stability, so this is expected.

However, the longer random examples in this Kata appeared to break this pattern, and equivalent length strings were rearranged in the array after the sort method. I'm not able to explain this behaviour.

I haven't looked at the source, so I'm just guessing, but probably the sorting algorithm used depends on the length of the array. Switching to unstable but faster one for larger array.

['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'].sort((a, b) => a.length - b.length);
['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']

['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a'].sort((a, b) => a.length - b.length);
['5', '0', '2', '3', '4', '1', '6', '7', '8', '9', 'a']

Looks like in-place quicksort and insertion sort is used (v8/src/js/array.js#L709-L1002).

// Insertion sort is faster for short arrays.
if (to - from <= 10) {
  InsertionSort(a, from, to);
  return;
}

Look into your solution.
The reason of it just because you've modified the original array ;-)

In C#:

Test2__100_Random_Tests
 Log
 Testing for: 
arr = []
Pass Value = []

In Python:

  Random Tests
 Log
 []
✔ Test Passed

Which language? JS?
But I test it got this:

100 Random Tests --- Testing for correctness of solution
  It should works for random tests.
 Log
 Testing for:
arr = [] 
✔ Test Passed: Value deep equals []

There never was a remark about that. I'm not the JS translator but the Codewarrior who translated it is excellent, since long.