Jquery mobile popup from php with if then

I searched the net on this:

i want to show a jquery mobile styled popup when an variable equals 0.

I tryed various solutions from javascript but no succes.

<div data-role="page" id="indexpage">
    <div data-role="popup" data-history="false" id="popupBasic"><br> Nothing to show     <br><br>
    </div>
</div>

if ($aantal_opnames === 0 ){
// show popup here

}

How can i invoke that ?