JSFiddle - React, Tailwind, and code Playground

HTML

<select id="options" class="auto-updater">
  <option value="" selected>Choose...</option>
  <option value="opt1Value1" >Option 1</option>
  <option value="opt1Value2" >Option 2</option>
</select>

<select id="options2" class="auto-updater">
  <option value="" selected>Choose...</option>
  <option value="opt2Value1" >Option 1</option>
  <option value="opt2Value2" >Option 2</option>
</select>

<input type="text" id="targetTextField" name="targetTextField" size="31" tabindex="0" maxlength="99">

JavaScript

$(".auto-updater").change(function() {
    var values = $(".auto-updater").map(function() {
        return ($(this).val() == "") ? null : $(this).val();
    }).get();
                         
    $("#targetTextField").val(values.join(','));
});