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($) {
        var promise = null;
        
        $('#first').change( function() {
            promise = $.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();
        promise.promise().done( function() {
            $('#second').val('b');
            console.log('setting value...');
        });
        
    })(jQuery);