I just published what I developped so far during the last days.
Here you can find the github project https://github.com/mar9000/ecmascript4mps
and here a small presentation http://mar9000.org/bliki/ecma-script-4-mps.html
I saw a similar project on github but it's quite old and probably less complete then mine with respect to supported constructs. ECMAScript4MPS is complete with respect to supported syntax.
It's just a draft work I know. I think to improve it in the future at least to make it usable in generation templates.
I would like to thank people from this forum who helped me when I did not have a clue.