He is using a recursive function. A function that calls it self.

Fixed

Same issue. I even tried making both the code and the tests return true; Still the error.
It looks like the kata framework itself is using toString(). (You can see this if you make the tests box empty.)

In fact, I even unlocked the existing solutions and copied one. The test still fails with this error.

This was the example given: "In the following 6 digit number:

283910

91 is the greatest sequence of 2 digits."

You can see that if you were about to pick the largest from right to left and left to right then 93 would be the return instead, but this picks 91. I think when they say largest "sequence" they mean from left to right only. Does that answer the question you were asking?

The JavaScript engine is running on Node.JS so there is no window or document object.

Can you explain more specific what exactly you need to do?

I am not sure, but if you dont apply second argument(0) in reduce method then the first argument(rem) in the callback function is a first value in array.If you add array to number you will get weird things i think.

This quite good solution,i didnt know you could pass into the callback function arguments in such way,i mean in array [on,off]

Nice!

ok, theres two things here, the reload and close function... and maybe another. But i think what your looking for it window.location.close(); or window.location.reload();