Build:
Install emscripten and make sure emcc is in your $PATH.
./buildall
see output for compiled results.
snem port is outdated, can only be compiled by a very old version of emscripten.
snes9x port is updated for emscripten 1.34.3

Note:
1 For snem port, I use a wrong and very unstable way to access Heap32. I simply assume Module.Heap32 is compiled to global variable i by closure. There are much better ways to do this, but variable i works for me so far, so I am too lazy to fix it.
2 There is a bug in library_sdl.js of current emscripten. library_sdl.js does not handle a-z keys correctly. Use snes9x/sdl/library_sdl.js to overwrite emcscripten/src/library_sdl.js to fix the bug.
3 It tooks about 1 min to compile snesEmu and another 1 min for snesWW* on my core i7-2600 machine. Compling snes9x requires about 7 min. 
4 Sounds and many other features of snes9x version are disabled for speed. You can enable them if you want. To enable the sound, simply add -DSOUND option to emcc (see snes9x/sdl/buildhtml).

More information:
http://tjwei.github.com/xnes  # Demo and information (brought your own roms)

Blog posts (Tradition Chinese)
http://weijr-note.blogspot.tw/2012/06/javascript-snes-emulator-wip.html # Orginal version (6/22/2012)
http://weijr-note.blogspot.tw/2012/08/js.html                   # more videos
http://weijr-note.blogspot.tw/2012/08/coscup-2012.html          # COSCUP slides