JSFiddle - React, Tailwind, and code Playground

HTML

<select id="one">
    <option>Option 1 - 1</option>
    <option>Option 1 - 2</option>
</select>
<select id="two">
    <option>Option 2 - 1</option>
    <option>Option 2 - 2</option>
</select>
<select id="three">
</select>

JavaScript

$('#one, #two').on('change',function() {
    $('#three').empty().append('<option>' + $("#one option:selected" ).text() + '</option>').append('<option>' + $("#two option:selected" ).text() + '</option>');
});