fetch('/changemgmt/listOutboundChangeSet.apexp', {
  credentials: 'same-origin'
}).then(function(response) {
  return response.text();
}).then(function(text) {
  var p = new DOMParser();
  var d = p.parseFromString(text, 'text/html');
  var thisOrgEl = d.getElementById('thisOrg');
  var sandboxName = thisOrgEl.children[0].innerText.split('\n')[0];
});