TypeError: Cannot set properties of undefined (setting 'num')

I have been receiving this error “TypeError: Cannot set properties of undefined (setting ‘num’)” when trying to run this code.

I would appreciate any help as I cannot get my head around it

How are you triggering this error?

using arrow keys to shift numbers in the game.

Well, it doesn’t seem to be doing anything for me. I’m pressing arrow keys and nothing is happening. Perhaps I don’t know how to use this properly? Maybe someone else will have better luck.

try clicking on the game a couple of times?

Ya, I have been. Actually, the last time I tried it the numbers did change once and then my browser told me that the page is too slow and it basically stopped executing your program. I think you might have some issues in your code that are causing it to eat up too much browser resources.

Also, it would really help if you explained a little more about what your program is supposed to do and how to use it. Most people aren’t going to have the time to go through your code and try to figure it out for themselves.