In this article, we’ll look at some methods of manipulating JavaScript to determine various network characteristics from within the browser — characteristics that were previously available only to applications that directly interface with the operating system. Much of this was discovered while building the Boomerang project to measure real user performance.
via Analyzing Network Characteristics Using JavaScript And The DOM, Part 1. Pretty sure I would never have thought of attempting measuring the speed of the TCP packest with JavaScript. I’ve done it a few times with C for a class, Atwood’s Law in effect, I guess.