JSFiddle - React, Tailwind, and code Playground

HTML

<select id="mySelect">
    <option value="1" id="opt1">Option 1</option>
    <option value="2" id="opt2">Option 2</option>
    <option value="3" id="opt3">Option 3</option>
    <option value="4" id="opt4">Option 4</option>
</select>

JavaScript

$(document).ready(function () {
    $('#opt3').prop('selected', 'selected').attr('selected', 'selected');
    $('#mySelect').attr('value', $('#mySelect').find(':selected').val());

    alert($('#opt3').prop('selected'));
    alert($('#mySelect').val());
    alert($('#opt3').attr('selected'));
});