Caesars Cipher

One of the simplest and most widely known ciphers is a Caesar cipher, also known as a shift cipher. In a shift cipher the meanings of the letters are shifted by some set amount.

A common modern use is the ROT13 cipher, where the values of the letters are shifted by 13 places. Thus A ↔ N, B ↔ O and so on.

Write a function which takes a ROT13 encoded string as input and returns a decoded string.

All letters will be uppercase. Do not transform any non-alphabetic character (i.e. spaces, punctuation), but do pass them on.

				
					function rot13(str) {
  let alphabetsGroup = [
   {
   	'?':'?',
   	'!':'!',
   	'.' : '.',
  ' ': ' ',
   	A: "N",
   	B: "O",
   	C: "P", 
   	D: "Q",
   	E: "R", 
   	F: "S", 
   	G: "T", 
   	H: "U",
   	I: "V", 
   	J: "W", 
   	K: "X", 
   	L: "Y",
   	M: "Z", 
   	N: "A", 
   	O: "B", 
   	P: "C",
   	Q: "D", 
   	R: "E", 
   	S: "F", 
   	T: "G",
   	U: "H",
   	V: "I",
   	W: "J", 
   	X: "K", 
   	Y: "L", 
   	Z: "M"
   }
  ];
  let newWord = [];

	for(let i = 0; i < str.length; i++){
			newWord.push(alphabetsGroup[0][str[i]])
	}
	return newWord.join('')
}
				
			
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