LAPTOP i7

Detect client speed using JavaScript

You can detect how long it toke for the browser to load the page. With load I mean the download time. Have a look at window.performance it contains all the timings. Also see html5rocks.

if (window.performance && window.performance.timing)
{
 var download_time = (window.performance.timing.responseEnd  - window.performance.timing.responseStart);
 var speed = ($(html).html().length) / download_time;
 if (speed < 400)
 {
 alert(slow);
 }
 else {
 alert(fast);
 }
}

Note that this works best it the page size is large. For small pages the TCP/IP overhead for is large compared to your download time. My page was about 19304 bytes and I was able to detect mobile vs desktop.

Also see this stackoverflow question.

This does not work for IE8 and Safari