Digital cypher vol 2.js

/*
Description:
Introduction
Digital Cypher assigns to each letter of the alphabet unique number. For example:

 a  b  c  d  e  f  g  h  i  j  k  l  m
 1  2  3  4  5  6  7  8  9 10 11 12 13
 n  o  p  q  r  s  t  u  v  w  x  y  z
14 15 16 17 18 19 20 21 22 23 24 25 26
Instead of letters in encrypted word we write the corresponding number, eg. The word scout:

 s  c  o  u  t
19  3 15 21 20
Then we add to each obtained digit consecutive digits from the key. For example. In case of key equal to 1939 :

   s  c  o  u  t
  19  3 15 21 20
 + 1  9  3  9  1
 ---------------
  20 12 18 30 21

   m  a  s  t  e  r  p  i  e  c  e
  13  1 19 20  5 18 16  9  5  3  5
+  1  9  3  9  1  9  3  9  1  9  3
  --------------------------------
  14 10 22 29  6 27 19 18  6  12 8
Task
Write a function that accepts an array of integers code and a key number. As the result, it should return string containg a decoded message from the code.

Input / Output
The code is a array of positive integers.
The key input is a positive integer.

Example
decode([ 20, 12, 18, 30, 21],1939);  ==> "scout"
decode([ 14, 10, 22, 29, 6, 27, 19, 18, 6, 12, 8],1939);  ==>  "masterpiece"
*/

function decode  (code, n) {
  const arr=n.toString().split('').map(Number)
  let arr2=code.slice();
  let arr3=[];
  for (let i=0,j=0;i<code.length;i++){
  if (j>=arr.length){j=0}
  arr3.push(arr2[i]-arr[j])
  j++}
    return arr3.map(v=>String.fromCharCode((v+96))).join('');
}