This Boolean Never Turns True
isChar becomes is true when the key is a character.
Simple enough, right?
Well... no. From the linked documentation:
There is currently a known bug affecting the return result, which is always
true. Please see the discussion link in the sidebar for more details.
Fortunately it's a known bug. Well, sort of. It's actually still marked "NEW" meaning no one at Mozilla has verified it exists. Or even looked at it.
Since October 2005. Two years ago.