I entered the following in Chrome's console:
decodeURIComponent('a%AFc');
Instead of resulting to a0xAFc, it caused a URIError exception (malformed uri).
I've heard several excuses why this may be possible, but what I don't understand is why?
The decodeURIComponent() function in particular is supposed to decode data, not verify the URI.
%AF is not a character on his own but part of Unicode sequence (MACRON - %C2%AF).
%AF wasn't produced by encodeURIComponent but something like escape, so it can be decoded by unescape.
What you probably need is decodeURIComponent('%C2%AF')