JSFiddle - React, Tailwind, and code Playground

HTML

<select name="firstselect">
   <option value="0" selected="selected">Choose...</option>
   <option value="1">Value1</option>
   <option value="2">Value2</option>
   <option value="3">Value3</option>
</select>

<select name="secondselect">
   <option value="0" selected="selected">Choose...</option>
   <option value="myclass1">Value11</option>
   <option value="myclass1">Value12</option>
   <option value="myclass1">Value13</option>
   <option value="myclass2">Value21</option>
   <option value="myclass2">Value22</option>
   <option value="myclass2">Value23</option>
   <option value="myclass3">Value31</option>
   <option value="myclass3">Value32</option>
   <option value="myclass3">Value33</option>
</select>

JavaScript

$(document).ready(function(){
    var cod = '';
    $('select[name="firstselect"]').change(function(){
        cod = $(this).val();
        if ( cod > 0 ) {
            $('select[name="secondselect"] option').hide().filter(function(){
               return ( $(this).val().substr(7,1) == cod || $(this).val() == 0 ); 
            }).show();
        }
    });
});