Making Cascade in Blocks Mandatory

To make cascade function mandatory in blocks add this code to the bootstrap layout section of your block product, below the layout area. In the main layout section.

<div class="col-md-12">

layout area here........

</div

<script>
jQuery('#btnPrev').on('mousedown', function(){
var product = jQuery('select')[0].value;
if(!product){
alert("Product is empty");
jQuery('#btnPrev').attr('disabled',true);
}else{
jQuery('#btnPrev').removeAttr('disabled');
}
})
$(document).ready(function() {
$(document).on('change', jQuery(jQuery('select')[0]), function(){
var product = jQuery('select')[0].value;
if(product){
jQuery('#btnPrev').removeAttr('disabled');
}else{ alert("Product is empty");
jQuery('#btnPrev').attr('disabled',true);}})
});