JSFiddle - React, Tailwind, and code Playground

HTML

<select id="first">
    <option value="">--</option>
    <option value="a">a</option>
</select>

<select id="second">
    <option value="">--</option>
    <option value="b">b</option>
</select>

JavaScript

$('button').click(function () {
    var first = $('#first').val();
    var second = $('#second').val();
    
    
});