How to detect nearest server to test latency/ping speed using Javascript?

Question

I'm implementing a browser extension which should connect to the nearest server to test the ping speed.

To have more details, kindly have a look on SpeedTest , it first calculates the ping time.
And to calculate this ping time, it detects the nearest servers and then pings it.

For example, here's the nearest servers detected by SpeedTest . I marked them in red arrows

How does SpeedTest detect these servers ?

ie How can I detect the nearest servers and their locations in javascript as SpeedTest does ?

Answer 1

What speedtest is doing is not a real "ping" in the sense of having the client machine run a ping operation. I have no knowledge of their exact methods (and I believe they use flash rather than pure JS, or at least used to), but I would guess that they try to access a small resource (an empty text/image file?) on each of these machines, and then time the response back. That is certainly one way to implement this anyway.