ROT13.js

/*
Description:
How can you tell an extrovert from an introvert at NSA? Va gur ryringbef, gur rkgebireg ybbxf ng gur BGURE thl'f fubrf.

I found this joke on USENET, but the punchline is scrambled. Maybe you can decipher it? According to Wikipedia, ROT13 (http://en.wikipedia.org/wiki/ROT13) is frequently used to obfuscate jokes on USENET.

Hint: For this task you're only supposed to substitue characters. Not spaces, punctuation, numbers etc. Test examples:

rot13("EBG13 rknzcyr.") == "ROT13 example.";
rot13("This is my first ROT13 excercise!" == "Guvf vf zl svefg EBG13 rkprepvfr!"
*/
function rot13(str) {
  let s1 = 'abcdefghijklmnopqrstuvwxyz'
  let s2 = 'NOPQRSTUVWXYZABCDEFGHIJKLM'.toLowerCase()
  const replaced = str.replace(/[a-z]/gi,v=>{
  let upper = v===v.toUpperCase()
    return upper?s2[s1.indexOf(v.toLowerCase())].toUpperCase():s2[s1.indexOf(v.toLowerCase())].toLowerCase()
  })
  return replaced
}