code: function handleQuery() {
    let query = parseQuery();
    let url = window.location.protocol + '//' + window.location.hostname + ':' +
              window.location.port + ELASTICSEARCH_INTERFACE_ROUTE;
    let httpRequest = new XMLHttpRequest();
  
    httpRequest.onreadystatechange = function() {
      if(httpRequest.readyState === XMLHttpRequest.DONE) {
        if(httpRequest.status === 200) {
          let response = JSON.parse(httpRequest.responseText);
          updateResults(response);
          updateHits(response);
          updateAggregations(response);
          show(queryResults);
        }
        else {
          queryError.textContent = 'Query returned status ' +
                                   httpRequest.status +
                                   '. Is Elasticsearch connected and running?';
          hide(queryResults);
          hide(queryButton);
          show(queryError);
        }
      }
    };
    httpRequest.open('POST', url);
    httpRequest.setRequestHeader('Content-Type', 'application/json');
    httpRequest.setRequestHeader('Accept', 'application/json');
    httpRequest.send(JSON.stringify(query));
  }
docs: Handle the current Elasticsearch query