JavaScript を使用してインターネット速度を測定するにはどうすればよいですか?

var imageAddr = "https://example.com/image.png";
var downloadSize = 7300000; //bytes

function MeasureConnectionSpeed() {
  var startTime, endTime;
  var download = new Image();
  download.onload = function () {
    endTime = (new Date()).getTime();
    showResults();
  };
  
  download.onerror = function (err, msg) {
    ShowProgressMessage("Invalid image, or error downloading");
  }
  
  startTime = (new Date()).getTime();
  var cacheBuster = "?nnn=" + startTime;
  download.src = imageAddr + cacheBuster;
  
  function showResults() {
    var duration = (endTime - startTime) / 1000; //seconds
    var bitsLoaded = downloadSize * 8;
    var speedBps = (bitsLoaded / duration).toFixed(2);
    var speedKbps = (speedBps / 1024).toFixed(2);
    var speedMbps = (speedKbps / 1024).toFixed(2);
    ShowProgressMessage("Your connection speed is:");
    ShowProgressMessage(speedBps + " bps");
    ShowProgressMessage(speedKbps + " kbps");
    ShowProgressMessage(speedMbps + " mbps");
  }
}