使用javascript计算速度

var imageAddr = "/images/image.jpg" + "?n=" + Math.random();
var startTime,endTime;
var downloadSize = 200000;
var download = new Image();
download.onload = function () {
    endTime = (new Date()).getTime();
    showResults();
}
startTime = (new Date()).getTime();
download.src = imageAddr;

function showResults() {
    var duration = Math.round((endTime - startTimE) / 1000);
    var bitsLoaded = downloadSize * 8;
    var speedBps = Math.round(bitsLoaded / duration);
    var speedKbps = (speedBps / 1024).toFixed(2);
    var speedMbps = (speedKbps / 1024).toFixed(2);
    alert("Your connection speed is: \n" + 
           speedBps + " bps\n"   + 
           speedKbps + " kbps\n" + 
           speedMbps + " Mbps\n" );
}