JSFiddle - React, Tailwind, and code Playground

HTML

<select class="founder_designation" rel="Designation" placeholder="Designation" multiple="multiple" name="designation">
<option value="">-- Select Designation --</option>
<option value="chairman_managing_director">Chairman &amp; Managing Director</option>
<option selected="selected" value="director" >Director</option>
<option value="whole_time_director">Whole Time Director</option>
<option value="other">Other</option>
</select>

JavaScript

$(".founder_designation").on("change",function(){
  alert($(this).val());   //It display all selected options with comma separated
})