JSFiddle - React, Tailwind, and code Playground

HTML

<p>An additional field (not displayed here) should be required if one of the input's values is not empty, or is not in the array of strings we consider "empty".</p>

<form>
    <fieldset>
        <p>If "No" is checked or nothing is checked, additional field should not be required. Otherwise it should be.</p>
        <label>Yes
            <input type="radio" name="option" value="Yes">
        </label>
        <label>No
            <input type="radio" name="option" value="No">
        </label>
        <label>N/A
            <input type="radio" name="option" value="n/a">
        </label>
        <button type="submit">Validate</button>
    </fieldset>
</form>

<form>
    <fieldset>
        <p>If the value is "no", "", "n/a", or "0", additional field should not be required (case insensitive). Otherwise it should be.</p>
        <label>Text
            <input type="text" name="option">
        </label>
        <button type="submit">Validate</button>
    </fieldset>
</form>

<form>
    <fieldset>
        <p>If the value is "no", "", "n/a", or "0", additional field should not be required (case insensitive). Otherwise it should be.</p>
        <label>Text
            <select name="option">
                <option value=""></option>
                <option value="Yes">Yes</option>
                <option value="No">No</option>
                <option value="n/a">n/a</option>
            </select>
        </label>
        <button type="submit">Validate</button>
    </fieldset>
</form>

CSS

body{font:12px arial}
.error{color:red}
.success{color:green}

JavaScript

/* This is the part I'm having trouble with */
function checkIfRequired(form) {

    var value = $('[name="option"]');
var type = value.attr("type");

if(type && type.toLowerCase() == 'radio')
  value = value.filter(":checked").val();
else
  value = value.val();
    
   
        empty = ['no', '', 'n/a', '0'];
    
    // If the input is not "empty", make the additional field required
    // inArray returns -1 if not found
    if ($.inArray(value.toLowerCase(), empty) < 0) {
        required = true;
    } else {
        required = false;
    }

    showResult(required, form);
}



/* Stuff for demo */
function showResult(required, form) {
    var message = required ? 'Additional field required' : 'Additional field not required';
    var status = required ? 'error' : 'success';
    $('.message').remove();
    $('fieldset', form).append('<div class="message ' + status + '">' + message + '</div>');
    $('.message').hide().fadeIn();
}
$('form').submit(function(e) {
    e.preventDefault();
    checkIfRequired(this); // We'll just pass the form object for the demo
});