How to detect internet speed in JavaScript?

Question

How can I create a JavaScript page that will detect the user’s internet speed and show it on the page? Something like “your internet speed is ??/?? Kb/s”.

Answer 1

Even though this is old and answered, i´d like to share the solution i made out of it 2020

it comes with the flexibility to run at anytime and run a callback if greater and or smaller the specified mbps

testConnectionSpeed:{
  imageAddr : "/app/images/test_connection.jpg" , // you have to adjust this
  downloadSize : 31291,// and this must match with file above ;) 
  run:function(mbps_max,cb_gt,cb_lt){
    testConnectionSpeed.mbps_max = parseFloat(mbps_max) ? parseFloat(mbps_max) : 0;
    testConnectionSpeed.cb_gt = cb_gt;
    testConnectionSpeed.cb_lt = cb_lt;
    testConnectionSpeed.InitiateSpeedDetection();
  },
  InitiateSpeedDetection: function() {
    window.setTimeout(testConnectionSpeed.MeasureConnectionSpeed, 1);
  },
  result:function(){
    var duration = (endTime - startTime) / 1000;
    var bitsLoaded = testConnectionSpeed.downloadSize * 8;
    var speedBps = (bitsLoaded / duration).toFixed(2);
    var speedKbps = (speedBps / 1024).toFixed(2);
    var speedMbps = (speedKbps / 1024).toFixed(2);
    if(speedMbps >= (testConnectionSpeed.max_mbps ? testConnectionSpeed.max_mbps : 1) ){
      testConnectionSpeed.cb_gt ? testConnectionSpeed.cb_gt() : false;
    }else {
      testConnectionSpeed.cb_lt ? testConnectionSpeed.cb_lt() : false;
    }
  },
  MeasureConnectionSpeed:function() {
    var download = new Image();
    download.onload = function () {
        endTime = (new Date()).getTime();
        testConnectionSpeed.result();
    }
    startTime = (new Date()).getTime();
    var cacheBuster = "?nnn=" + startTime;
    download.src = testConnectionSpeed.imageAddr + cacheBuster;
  }
}

you can then start the test anywhere after you included the snippet above by running the testConnectionSpeed.run(mbps, morefunction, lessfunction)

for example:

testConnectionSpeed.run(1.5, function(){console.log(">= 1.5Mbps")}, function(){console.log("< 1.5Mbps")} )

(the larger the image, the more reasonable the test)