JSFiddle - React, Tailwind, and code Playground

HTML

<select>
    <option>aaaaa</option>
    <option>bbbbb</option>
    <option>ccccc</option>
</select>

<button>button</button>

JavaScript

(function($) {
    "use strict";
    $.fn.openSelect = function()
    {
        return this.each(function(idx,domEl) {
            if (document.createEvent) {
                var event = document.createEvent("MouseEvents");
                event.initMouseEvent("mousedown", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
                domEl.dispatchEvent(event);
            } else if (element.fireEvent) {
                domEl.fireEvent("onmousedown");
            }
        });
    }
}(jQuery));

$('button').on('click', function() {
    $('select').openSelect();
});