That is the priority that your filter is called. All of the built in ACF filters and actions are called with a priority of 10. So if you want to run your before ACF then you use a number < 10 and if you want them to run after you use a priority > 10. Since we want ACF to have already saved the fields when we try to get them we want > 10 in this case.
I would try to figure out the JS for more help, I’m sure the code would come in handy in the future, if I had time to kill, but as development goes, I am going through a peak at the moment. I come here and answer questions when I need to give my brain a break from whatever I’m working on.
