The code my clarify that up, it simply calculate how much time an http request take to complete:

  function ping_test() {
     time_request("http://ping.projects.chrisjeakle.com/ping/data.txt", "result-east");
     time_request("http://ping.projects-west.chrisjeakle.com/ping/data.txt", "result-west");
  }

  function time_request(url, output_id) {
      document.getElementById(output_id).innerText = "...";
      const start_time = new Date().getTime();
      fetch(url, {
          mode: "no-cors",
          cache: "no-cache",
        }).then(async (result) => {
          const elapsed_time = new Date().getTime() - start_time;
          document.getElementById(output_id).innerText = elapsed_time;
      });
  }