<div mnt-watch-product="ZAL-BE-DP521I09O-K11">
 <button type="button" onclick="Monotote.show('ZAL-BE-DP521I09O-K11')">View details</button>
 <span>The product is not available</span>
</div>
<script>
 // define `_mnt` with a `publisherKey`
 _mnt.onReady = function(){
   Monotote.on("watch-product-availability-state-change", function(info){
     // it contains `element` and `available` properties
     info.element.className = info.available ? '' : 'disable-product';
   });
 }
</script>
<style>
 div span {
   display: none;
 }
 div.disable-product button {
   display: none;
 }
 div.disable-product span {
   display: initial;
 }
</style>