Async Await/Promise not implemented?

I try to understand the Await/Promise concept that according to the pas2js wiki should be built in into the compiler. But if I just enter this code

Procedure AsyncCall; async;  <-- Syntax Error

I get a "Syntax error" from the compiler with no further explanations.

Is this feature probably switched off somehow?

Also, I could not find a demo in the TMS demos that uses this feature. Does this mean it's of no use? If so, what is the best replacement practice?

The wiki is about the pas2js trunc version.
At this moment we validated and include pas2js 1.4.30 that does not have this feature yet.
We work with the pas2js team to incorporate a newer version in the near future but there are several more things to complete, check, test, validate ...