After reading [Peter's article on JavaScript](http://peter.michaux.ca/articles/javascript-is-dead-long-live-javascript) I noticed

> 
> Brendan Eich stated that one the goals for Harmony is to be a better target for to-JavaScript compilers.
> 
> 
> 

There are currently two popular compilers with some vague [ES:Harmony](http://wiki.ecmascript.org/doku.php?id=harmony%3aproposals) compliance:

* [Traceur](https://github.com/google/traceur-compiler)
* [CoffeeScript](http://jashkenas.github.com/coffee-script/)

Although CoffeeScript has some compliance it's not designed to be an ES:Harmony compiler so it's not useful to this end.

Tracuer seems to be sticking more rigorously to the ES:Harmony specification but I don't know whether it intends to become a full ES:Harmony compiler.

Since the aim is to to compile ES6 down to ES3 it would also need to support ES5 features (and probably a switch whether to compile ES5 to ES3 or ES6 to ES3). 

1. Are there currently any other projects aiming to create a full ES:Harmony to ES3 compiler?
2. Is it wise to start writing such a compiler knowing that the standard is young / unstable / in flux.
3. Are there currently any ES5 -> ES3 compilers?

I've left a question on the [Traceur mailing list](http://groups.google.com/group/traceur-compiler-discuss/browse_thread/thread/2974b8ed9705110c).

The aim of such a compiler would be backwards compatibility with ES3. Not full emulation of ES5 and ES6 in ES3.