JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <select id="first">
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
    </select>
    <select id="second"></select>
</div>

JavaScript

$( function() {
    $('#first').change( function() {
        $.ajax({
            url: "#"
        }).done(function() {
            $('#second').append(
                '<option value="a">a</option>'+
                '<option value="b">b</option>'+
                '<option value="c">c</option>'
            );
            console.log('appending new content...');
        });
    });
    
    $('#first').val('2').change();
    $('#wrapper').promise().then( function() {
        $('#second').val('b');
        console.log('setting value...');
    });
    
});