JSFiddle - React, Tailwind, and code Playground

HTML

do you mean this?
<select>
  <option value="yaya">1</option>
  <option value="something">2</option>
</select>

<input type="text"/>

JavaScript

$(".document").ready(function(){
     someString = "this,that";
        $("input").autocomplete({source: someString.split(",")}); 

    $("select").change(function(){
        alert($(this).val()+" appended");
someString = someString+","+$(this).val();
        $("input").autocomplete({source: someString.split(",")}); 


    });
});