JSFiddle - React, Tailwind, and code Playground

HTML

<input type="radio" id="need_staff_on_site" name="data[CaterRequest][need_staff_on_site]" value="yes" class="staff_on_site"><span>Yes</span>

<input type="radio" id="need_staff_on_site" name="data[CaterRequest][need_staff_on_site]" class="staff_on_site" value="no"><span>No</span>

How many staff?<input type="text" maxlength="3" id="no_of_staff" name="data[CaterRequest][staff_needed]" class="txtboxSml2" readonly="readonly">

JavaScript

$(document).ready(function(){

   $('.staff_on_site').click(function(){

     var rBtnVal = $(this).val();

     if(rBtnVal == "yes"){
         $("#no_of_staff").attr("readonly", false); 
     }
     else{ 
         $("#no_of_staff").attr("readonly", true); 
     }
   });
});