Determine client's connection speed with JavaScript

bandwidth.js

// Let's initialize the primitives
var startTime, endTime, fileSize;

// Set up the AJAX to perform
var xhr = new XMLHttpRequest();

// Rig the call-back... THE important part
xhr.onreadystatechange = function () {

  // we only need to know when the request has completed
  if (xhr.readyState === 4 && xhr.status === 200) {

    // Here we stop the timer & register end time
    endTime = (new Date()).getTime();

    // Also, calculate the file-size which has transferred
    fileSize = xhr.responseText.length;
    // N.B: fileSize reports number of Bytes

    // Calculate the connection-speed
    var speed = fileSize / ((endTime - startTime)/1000) / 1024;
    // Use (fileSize * 8) instead of fileSize for kBps instead of kbps

    // Report the result, or have fries with it...
    console.log(speed + " kbps\n");
  }
}

// Snap back; here's where we start the timer
startTime = (new Date()).getTime();

// All set, let's hit it!
xhr.open("GET", "URL/TO/PROBE.FILE", true);
xhr.send();

What are you calculating the connection speed in, Kibibits, Kilobits, etc?

A bit confused by the formula.

What are you calculating the connection speed in, Kibibits, Kilobits, etc?

A bit confused by the formula.

Check line #23

What are you calculating the connection speed in, Kibibits, Kilobits, etc?
A bit confused by the formula.

Check line #23

Your units are wrong. KBps is kilobytes per second, but it should be kbps - kilobits per second
fileSize is in Bytes, because length property is number of characters, where each character is 8 bits long = 1 Byte
your formula is:
speed = (fileSize * 8) / ((endTime - startTime)/1000) / 1024
speed = (size in bits) / (time in seconds) / 1024
so it's kilobits/s = kbps, not kilobytes/s = kBps

@ffilopeter you're correct. I've just updated it. Thanks!

@ffilopeter you're correct. I've just updated it. Thanks!

Thanks for the gist. Just a quick heads up: seems like there still is some mix up with the units on lines 22 and 25. Unless I am wrong, it should read like this.

`
// Use (fileSize * 8) instead of fileSize for kbps instead of kBps

// Report the result, or have fries with it...
console.log(speed + " kbps\n");

`

@celsobessa I must have had a brain-fart the last time I tried to "fix" it.
Thanks for pointing it out. How does it look now?