Detect internet speed in Javascript // ref. : http://jsfiddle.net/yahavbr/tEFpC/2/ http://stackoverflow.com/questions/5529718/how-to-detect-internet-speed-in-javascript

detectBandwidth.js

var imageAddr = "http://www.tranquilmusic.ca/images/cats/Cat2.JPG" + "?n=" + Math.random();
var startTime, endTime;
var downloadSize = 5616998;
var download = new Image();
download.onload = function () {
    endTime = (new Date()).getTime();
    showResults();
}
startTime = (new Date()).getTime();
download.src = imageAddr;

function showResults() {
    var duration = (endTime - startTime) / 1000; //Math.round()
    var bitsLoaded = downloadSize * 8;
    var speedBps = (bitsLoaded / duration).toFixed(2);
    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" );
}

https://developer.mozilla.org/en-US/docs/Web/API/NetworkInformation/downlink

It still an experimental feature, so the script above seem a legit workaround, thanks!

For what it's worth, Mozilla still reports Chrome (and by my testing Opera) caps the downlink speed to 10Mb/s to avoid fingerprinting. What a shame web advertisers have ruined specificity on an otherwise helpful feature to determine download speed. In general, the downlink feature can still be used to determine a disadvantaged client (slow downlink) vs a speedy client.

The image/website no longer exists, and therefore this code is broken. It needs to be replaced with an image of the same size.