Incorrect comparison of two keyCodes in async function after dart2js
This is indeed the same as this bug.
The wrong type was inferred for the iteration variable of async for loops.
It is fixed in 1.10.
This must be 1.9.3 dart2js bug.
I use now Dart SDK version 1.10.0-dev.1.5 and everything works fine. This is only solution what I found, if I want use 'await for'.