<?php
  $xsDatatemp = file_get_contents('js/xs.dat');
  $xsDatatemp = json_decode($xsDatatemp);
  $oldxs = $_POST['oldxs'];
  $newxs = $_POST['newxs'];
  $key = array_search($oldxs, $xsDatatemp);
  if ($key !== false) {
    $xsDatatemp[$key] = $newxs;
  }
  $newdata = json_encode($xsDatatemp);
  file_put_contents("js/xs.dat", $newdata);
?>