Firste-Reverse.js Code Challenge day 4

function FirstReverse(str) {
  // the new string, reversed, that will be returned.
  let newString = '';
  // at each iteration, i is the size of the string less one (right index),
  // while str.length - 1 is above zero,
  // subtract 1
  for (var i = str.length - 1; i >= 0; i--) {
    // at each index iteration, the newString will receive a character that is the
    // character at the current index (str.length -1),
    // then the index will shorten by one at every iteration.
    newString = newString + str.charAt(i);
  }

  return newString;
}

// OR

function FirstReverse2(str) {
  // first we split the string which creates an array of characters, e.g. ['c','a','t']
  // then we call the reverse function on this array
  // and finally we turn the reversed array back into a string using the join function
  return str
    .split('')
    .reverse()
    .join('');
}

FirstReverse2(readline());