<!DOCTYPE html>
<script>
function fetch_url(url) {
  return new Promise(function(resolve, reject) {
      var request = new XMLHttpRequest();
      request.addEventListener('load', function(event) {
          if (request.status == 200)
            resolve(request.response);
          else
            reject(new Error('fetch_url: ' + request.statusText + " : " + url));
        });
      request.addEventListener('error', function(event) {
          reject(new Error('fetch_url encountered an error: ' + url));
        });
      request.addEventListener('abort', function(event) {
          reject(new Error('fetch_url was aborted: ' + url));
        });
      request.open('GET', url);
      request.send();
    });
}
</script>