The tests of this kata don't take into account empty array elements. E.g.

let arr = [0,1,2,,,5]; // [0, 1, 2, empty, empty, 5]
arr.reverse(); // [5, empty, empty, 2, 1, 0]


With a simple exchange of values, we will get the value undefined instead of empty elements:

arr.reverse(); // [5, undefined, undefined, 2, 1, 0]


This Kata has a mistake in the description or in JavaScript tests.
Kаtа Description: "Any activities completed that are ranking 2 levels or more lower than the user's ranking will be ignored".
But tests require that progress in these cases is still increased by 1, and not ignored.
Please correct either the description or the tests!