Interesting, thanks for the sample. This sounds like its worth looking into.
In the meantime, you could do something like the following:
#if html5
untyped __js__ ("alert ('foobarstring')");
#end
…or
#if html5
import js.Browser;
#end
...
#if html5
Browser.alert ("Hello!");
#end
…or
stage.window.alert ("Hello!");
There’s a lot of ways to access and write JavaScript directly when you’re publishing to the HTML5 target
EDIT: …and in this exact case, the Lime window.alert
API should also work cross-target, so it shows an alert pop-up on the desktop as well (no support for mobile yet)