JSFiddle - React, Tailwind, and code Playground

HTML

<select id="options">
  <option value="" selected>Choose...</option>
  <option value="opt1Value1" >Option 1</option>
  <option value="opt1Value2" >Option 2</option>
</select>
<select id="options2">
  <option value="" selected>Choose...</option>
  <option value="opt2Value1" >Option 1</option>
  <option value="opt2Value2" >Option 2</option>
</select>
<input id="options3" type="text"/>
<input type="text" id="targetTextField" name="targetTextField" size="31" tabindex="0" maxlength="99">

JavaScript

$(function() {
$("#options").change(function(){
        setTarget()
});
    $("#options2").change(function(){
        setTarget();
});
    $("#options3").change(function(){
        setTarget();
});
});

function setTarget(){
    var tmp = $("#options").val();
    tmp += $("#options2").val();
    tmp += $("#options3").val();
    $('#targetTextField').val(tmp);
}