You can actually get the upper case version of the letters, since String.prototype.toUpperCase() exists, and we have capital U and capital C

[ghost]

Basically the title

[BeckTimothy]

the null value for those characters in MAPPING doesn't mean that we can't access them, but that there isn't a more easily accessible way to them that's smaller than 3600ish characters. Using h.toUpperCase is 5922 characters as opposed to the 3550 characters H costs using the methods in the replaceStrings functions of jsfuck.js

[hazzik]

This is how it was a loooooong time ago. It "costs" a lot of characters.