[AshleysBrain]

I don't think that's actually true. The way it use asynchronous callbacks allows for lots of parallelism. For example creating a new image will cause it to download the image off the network and decompress it in parallel to executing Javascript, and then when done it fires the 'onload' handler. That's much more parallel-by-design than something like C++.

[pcwalton]

Unfortunately you can't actually run those callbacks in parallel, because of JavaScript's run to completion model.

The work we're doing with PJs, however, attempts to fix this problem :)