JSFiddle - React, Tailwind, and code Playground

HTML

<select>
    <option value="a">a</option>
    <option value="b" selected="selected">B</option>
    <option value="c">C</option>
    <option value="d">d</option>
    <option value="e">e</option>
    <option value="f">f</option>
    <option value="g">g</option>
</select>
<button id="btn">Click me</button>

JavaScript

$('#btn').click(function(){
    alert($('select option:selected').text());
    $('select>option:selected').removeAttr('selected');
    $('select>option:nth-child(4)').attr('selected', true);
    alert($('select option:selected').text());
});