JSFiddle - React, Tailwind, and code Playground

by Cvrle

HTML

<select name="select_one" id="select_one" onChange="return showSelectedData(this.value, document.getElementById('select_two').value)">
<option value="">0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>

<select name="select_two" id="select_two" onChange="return showSelectedData(document.getElementById('select_one').value, this.value)">
<option value="1-0">1-0</option>
<option value="1-1">1-1</option>
<option value="1-2">1-2</option>
<option value="1-3">1-3</option>
</select>

JavaScript

function showSelectedData(select_ID_one, select_ID_two){
    alert("Selected value from first select box: "+select_ID_one);
    alert("Selected value from second select box: "+select_ID_two);
}