JavaScript validation action not working on mobile

I have this piece of JS code that aims to conditionally present form fields based on earlier selections. This works as expected on non-mobile devices. But, on mobile devices it does not. Here is code. I am working on andriod and have not checked any IoS devices. Any help is greatly appreciated.

switch (event.value) {

   case "Australia":

       this.getField("q8_input8").setItems(["-","O1","O2","O3", "O4"]);

       break;

case "South America & Canada":

       this.getField("q8_input8").setItems(["SAC1","SAC2","SAC3", "SAC4"]);

       break;

}

if(event.value)   this.getField("q8_input8").display = display.visible;

else   this.getField("q8_input8").display = display.hidden;