You seem to have an extra character in here:

*** a.js        2017-04-08 10:39:08.489905687 -0600
--- b.js        2017-04-08 10:39:26.520011065 -0600
***************
*** 8,14 ****
  var Base64 = {
  
        // private property
!       _keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",
  
        // public method for encoding
        encode : function (input) {
--- 8,14 ----
  var Base64 = {
  
        // private property
!       _keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/",
  
        // public method for encoding
        encode : function (input) {

Re: @Marti:
Honestly? I don't know, it's just an import needed in my script, and it works in context of my script. I'll try to get some test data in a meantime and test code for edge cases.

PS: Duh, no notifications about new issues...?

Re: @marsjaninzmarsa:

... and it works in context of my script

Probably, you are the expert with its current usage, but I would reupload it named as a Custom Base65 in whatever context. Shouldn't confuse potential Authors that may need actual Base64 in a library. I couldn't find any specification on Base65 but doesn't mean it doesn't exist somewhere as a custom base with a custom alphabet.

PS: ... no notifications about new issues...?

Best we can offer, at the moment, is you checking https://openuserjs.org/users/marsjaninzmarsa/scripts while logged in for an open issue bubble notice. We definitely don't collect e-mail addresses at this time. Re-read the Privacy Policy link at the bottom of every page. :)