function checkStatus(response) {
    // Throws error if http status is not success
    // Assumes the request body is the error message
    if (response.status >= 200 && response.status < 300) {
      return response;
    } else {
      return response.text().then(function (body) {
        throw new Error(body);
      });
    }
}

function postItem(url) {
  // posts an Item to URL, with the data in the form #item_edit_form
  // this can be used for new Items, or to update an item, since they use the same form
  fetch(url, {
    credentials: 'same-origin', //send cookies
    method: 'post',
    body: new FormData($("#item_edit_form"))
  })
  .then(checkStatus)
  .then(function(response) {
    return response.text();
  })
  .then(function(body) {
    if ( body == 'ok'){
      // item saved successfully
      Navigation.goBack();
    } else {
      // re-render the form with HTML received from server
      // most likely there are validation errors
      $(".page-content").innerHTML = body;
      componentHandler.upgradeDom();
    }
  })
  .catch(function(err) {
    // unexpected error when requesting data
    alert('Request failed: ' + err.message);
  });
}