AR Script: Custom photo counter (Pre-Batch)

const ZERO_PAD = 3;
const FILE_PREFIX = "";
const SEP = "_";
var reEdited = /.+?E\d/;
var temp_file = app.getItem(0).name;
var file_counter = 1;

// Function that add leading zeros to any string
function zpad(str, nb_digits) {
    if (str.length < nb_digits) { return (Array(nb_digits - str.length + 1).join('0') + str); }
    else { return str; }
}

function unEdited(filename){
  var isEdited = reEdited.test(filename);
  if (isEdited){  return [filename.substr(0, filename.length - 2), filename.substr(filename.length - 2, filename.length)]; }
  else {          return [filename, ""]; }

}