ECMAScript 4 was implemented in ActionScript 3[1]; a very nice language to work with IMHO. The members of the ECMAScript steering group launched into a public fracas on their respective blogs[2] which eventually ended in the draft being canned, despite the fact both ActionScript and Silverlight were already based on the standard... shame.
[1] http://en.wikipedia.org/wiki/ActionScript#ActionScript_3.0
[2] http://blogs.msdn.com/b/ie/archive/2007/10/30/ecmascript-3-a...