gistfile1.js

function makeRequest(url) {
  httpRequest = new XMLHttpRequest();
  var start = new Date().getTime();
  var stopTimer = function(){ 
    if (httpRequest.readyState == 4){
      var time = new Date().getTime() - start; 
      document.write(time<100?".":(time>600?" ":"-"));
      console.log(time);
      makeRequest(url);
    };
  }
  httpRequest.onreadystatechange = stopTimer;
  httpRequest.open('GET', url + '?_' + Math.random());
  httpRequest.send();
}
makeRequest('/puzzle');