This is so cool.

What about joining with gibberish characters?

Nice simple for loop. Less debatable than my reduce function.

Why? You are reducing to a single number according to the data ops. The only time there is no operation on that number is for operation o , which just pushes the number to the main function's output array. Seems pretty straightforward.
I've done it a bit differently in that my reduce function builds the main output array but I like this top solution, focusing on the number itself.

Make sure to run a Minifier on this code to decrease the amount of characters. It will be more readable.

I think it's over-documented. To me it's simpler to make the code shorter (reasonably), thus more readable by itself.

Looping does not need to go through the end. It can stop much sooner if both even/odd arrays have at least 3 values, and each of them has at least 1 value.

Instructions say that the arrays can be huge. Which means we probably should worry about it.
A proper, performant solution is still readable for this problem.

You could do return divisibleX && divisibleY only, itll return true if true and false otherwise by itself

The starting string must absolutely not be > 139 characters. 139 chars will allow you to add an hashtag if the provided string is 139 actual (eg no stripped spaces) chars