A simple asynchonous recursion-based speed test using the XMLHttpRequest API
To run, integrate it into an HTML file using <script src="..."></script> and call the main function as seen in speedtest.js
In order to prevent cacheing of images, I used a technique called cache busting. A random Base64 string is attached to the end of each URL as a query. Since the servers ignore the query (in this case) but browsers do not, the browser re-downloads the "different" image in almost all scenarios (since the chance that two Base64 strings of length 12 are the same is 1 ÷ 64 12 = 2.12 * 10 -22)