MESS has also recently been ported to JavaScript using the C/C++-to-JS transcompiler Emscripten; this port is called [http://jsmess.textfiles.com/ JSMESS] and is considered to be in its beta stage. Particularly sound is still a problem.
Out of the box only a small selection of MESS machines can be immediately compiled to JavaScript from the JSMESS package. Compiling MESS in its entirety would create a JavaScript file that is far too big for web browsers to handle. So one has to find out which parts of MESS are really needed for a given machine and create Makefiles with that subset. (JSMESS now also includes scripts that automate this task.) It is recommended to build JSMESS modules on Linux which also makes it easier to install the dependencies for Emscripten. The basis for JSMESS is MESS 0.142 and a custom version of Emscripten.
A [https://github.com/mdoege/jsmess JSMESS fork] that includes the necessary Makefiles to build the CPC 6128 version exists.