Javascript code to work in iOS

These will work as separate actions in IE when assigned to a Yes Checkbox, they will not work in iOS

Action1

var nShow = event.target.isBoxChecked(1)?display.hidden:display.visible;

this.getField("app.074SRG1100IssueDate").display = nHide;

this.getField("app.075SRG1100ExpiryDate").display = nHide;

Action2

var nShow = event.target.isBoxChecked(1)?display.hidden:display.visible;

this.getField("app.074SRG1100IssueDate").display = nShow;

this.getField("app.075SRG1100ExpiryDate").display = nShow;

On the No Checkbox

Action1

var nHide = event.target.isBoxChecked(1)?display.hidden:display.visible;

this.getField("app.074SRG1100IssueDate").display = nHide;

this.getField("app.075SRG1100ExpiryDate").display = nHide;

In iOS, the checkboxes work fine but not the hide/unhide element.

Help please