Try putting it here:
if keys[0] in allLetters:
textFill +=upper(keys[0])
Or:
if keys[0] in allLetters:
textFill +=keys[0]
textFill = upper(textFill)
Although, I’m not too terribly familiar with the way you’re adding letters. I use the ''.join() method.
For the python to JS thing, there are a few functions that don’t translate well. One of the major issues is with import functions because they don’t exist in JS. Save yourself a TON of trouble later by avoiding those at all cost now. Check out this thread and this crib sheet for help with translations! I’m honestly glad I mentioned the import function because fixing that later is not fun.