observer_form_rhon.js

var parentBody = document.getElementsByClassName("bodyclass")[0];

var observer = new MutationObserver(function (mutations, myObserver) {
  var _iteratorNormalCompletion = true;
  var _didIteratorError = false;
  var _iteratorError = undefined;

  try {
    for (var _iterator = mutations[Symbol.iterator](), _step; !(_iteratorNormalCompletion = (_step = _iterator.next()).done); _iteratorNormalCompletion = true) {
      var mutation = _step.value;

      mutation.addedNodes.forEach(function (x) {
        if (x.childNodes.length === 2) {
          dataLayer.push({
            event: 'formSent'
          });
          myObserver.disconnect();
        } else {
          myObserver.disconnect();
        }
      });
    }
  } catch (err) {
    _didIteratorError = true;
    _iteratorError = err;
  } finally {
    try {
      if (!_iteratorNormalCompletion && _iterator.return) {
        _iterator.return();
      }
    } finally {
      if (_didIteratorError) {
        throw _iteratorError;
      }
    }
  }
});

document.getElementById("boton-enviar").addEventListener('click', function () {
  observer.observe(parentBody, {
    childList: true,
    subtree: true,
    attributeOldValue: true
  });
});