code: function xhr(url, callback, data) {
          if (!window.XMLHttpRequest || !window.JSON) return;
  
          var request = new XMLHttpRequest();
          request.onreadystatechange = function() {
              if (callback && request.readyState == 4 && request.status == 200) {
                  // server MUST return JSON text
                  callback(JSON.parse(request.responseText));
              }
          };
          request.open('POST', url);
  
          var formData = new FormData();
  
          // you're passing "message" parameter
          formData.append('message', data);
  
          request.send(formData);
      }
docs: a simple function to make XMLHttpRequests