:thumb_up:

IMO it depends. Javascript is a chimera. Maybe you want to mutate the object! But in a pure functional world this is a sin.

Nice one with the "pageItemCount". I've done with 3 ifs :-)

Thats a nicely written and readable code. Great work!

man, i made my solution way extra longer. maybe i got intimidated by not knowing class/constructor Lol

wrapping all with a Math.abs() should do the trick

Isn't the pageIndex function wrong in case you ask for the last item at the end of the array (the item which equals to collection.length)?
It's returning -1 instead of the page index that equals to the last page.
This works because the test used in this kata doesn't check for the very last item of the array.

IMHO you should destructure you collection or create a new collection object elsewhere. With your current implementation a user cab mutate source collection (i.e. PaginationHelper.prototype.sortPages() etc).

Condition in pageItemCount is not correct;

pageIndex should be more or equal than zero, otherwise if it less, this method should return -1;

The feint with min is really clever! Thanks to the author!

I don't like this string conversion having iterators in

Are you sure?