JSFiddle - React, Tailwind, and code Playground

by TrueBlueAussie

HTML

<select name="CustomerType" id="CustomerType" class="form-control">
    <option value="10" selected="true">Company</option>
    <option value="20" selected="false">Person</option>
</select>

<input type="text" name="TaxNumber" id="TaxNumber" class="form-control parsley-validated"/>

CSS

.box {
    border: 1px solid red;
    height: 200px;
    overflow: auto;
}

.box-inner {
    height: 400px;
}

JavaScript

// Shortcut DOM ready handler
$(function(){
    // Listen for change event
    $('#CustomerType').change(function(){
        // Use jQuery val() to get select values
         var customerType = $(this).val();
         if (customerType == 10) {
            $("#TaxNumber").attr("data-required", 'false');
         }
         if (customerType == 20) {
            $("#TaxNumber").attr("data-required", 'true');
         }
    });
});