Voiceover detection in JavaScript

I've recommended this for use in iOS apps before, but am trying to see if this is also doable using JavaScript in Safari.

Weirdly enough I can't find this documented anywhere by anyone on the web, but this is an important feature for UI morphing within mobile web apps to address accessibility.

Specifically, the following won't work in Safari:

alert( UIAccessibilityIsVoiceOverRunning() );

Which appears to break the running of JavaScript on the page.

So, how is it possible to detect Voiceover within Safari using JavaScript?
Thanks,
Bryan