Write a JavaScript to replace each character of a given string by the next one in the English alphabet

function alphabet_char_Shift(str) {
  var all_chars = str.split("");
  for(var i = 0; i < all_chars.length; i++) {
    var n = all_chars[i].charCodeAt() - 'a'.charCodeAt();
    n = (n + 1) % 26; 
    all_chars[i] = String.fromCharCode(n + 'a'.charCodeAt());
  }
  return all_chars.join("");
}

console.log(alphabet_char_Shift("abcdxyz"))