How can I add the 'required' attribute to input on change of textarea?

Question

I need to add the required attribute to an html select (toDept) under the condition that a textarea (orderComments) has text typed in it. Below is my code... What am I missing? Do I need to run my jquery on a change event or something?

    $(document).ready(function() {
          if ($('#textareaId').val() != '') {
            $("#selectId").attr('required', true);
          }
        }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<textarea id="textareaId"></textarea>

<select id="selectId">
  <option value=""></option>
  <option value="opt1">opt1</option>
</select>

Thanks for your time!

Answer 1

You need to run the code when the textarea changes:

var textarea = $('#textareaId');
var select = $('#selectId');

var addOrRemoveRequiredAttribute = function () {
    if (textarea.val().length) {
        select.attr('required', true);
    }
    else {
        select.attr('required', false);
    }
};

// Run now
addOrRemoveRequiredAttribute();

// And when textarea changes
textarea.on('change', addOrRemoveRequiredAttribute);