... and TraceMonkey was based on open-sourced Macromedia/Adobe code from the ActionScript 3 VM. AS3 was loosely based on a draft of the ill-fated ES 4, but I'm

... and TraceMonkey was based on open-sourced Macromedia/Adobe code from the ActionScript 3 VM. AS3 was loosely based on a draft of the ill-fated ES 4, but I'm not sure if it was a strict superset of an earlier ECMAScript standard. It's possible that the Flash AS3 VM had been JITing all of ES2 or ES3 earlier than TraceMonkey came out.