url-parameter-appender.js

(function () {
  var urlParams = new URLSearchParams(window.location.search);
  var paramsToAppend = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content', 'gclid', 'ref', '_gl'];
  var formButton = document.querySelector('.button_class');

  if (formButton) {
    var dataUrl = formButton.getAttribute('data-url');

    if (dataUrl) {
      var url = new URL(dataUrl);

      paramsToAppend.forEach(function (param) {
        if (urlParams.has(param)) {
          url.searchParams.set(param, urlParams.get(param));
        }
      });

      formButton.setAttribute('data-url', url.toString());
    }
  }
})();