The grammar at the bellow link uses LALR parser(see [Changelog][1]) same as Yacc, I think is much closer to what you need than ANTLR wich usees LL according to this answer:
Can a ANTLR grammar file be modified to be used by PLY?
You can find the LALR Ecmascript grammar here: http://scriptonite.cvs.sourceforge.net/viewvc/scriptonite/scriptonite/src/ecmascript.grammar?revision=1.7
