Maxime Bouroumeau-Fuseau sent over a note about a project that's been started to try to port as much of PHP over to Javascript as possible - the Harmony Framework.

Nearly all of php features are already supported and the process is nearly instantaneous! Harmony also comes with Harmony XML, a Flex MXML like language to create components in xml and php.

The homepage even has a converter that you can use to make the PHP->Javascript transition for your own scripts. The framework is still in a Preview stage, but it already looks promising.