JSFiddle - React, Tailwind, and code Playground

HTML

<select id="s1">
    <option>--</option><option selected="selected">1</option>
    <option>2</option>
    <option>3</option>
    <option>4</option>
</select>

JavaScript

var showDropdown = function (element) {
    var event;
    event = document.createEvent('MouseEvents');
    event.initMouseEvent('mousedown', true, true, window);
    element.dispatchEvent(event);
};

setTimeout(function(){
    var focused = false;
    if($('#s1').is(":focus")) {
        $('#s1').blur();
        focused = true;
    }
    $('#s1').append("<option>NEW</option>");
    if(focused) {
        showDropdown($('#s1')[0]);
    }
},4000);