JSFiddle - React, Tailwind, and code Playground

HTML

<button id='btn'>Click here to expand dropdown</button>
<select id='sel'>
    <option>item 1</option>
    <option>item 2</option>
    <option>item 3</option>
    <option>item 4</option>
</select>

JavaScript

$(document).ready(function() {
    $("#btn").click(function() {
       // $("#sel").simulate('click');
        openDropdown("sel");
    });
});

//https://stackoverflow.com/a/10844589/7926961
  function openDropdown(elementId) {
        function down() {
            var pos = $(this).offset(); // remember position
            var len = $(this).find("option").length;
                if(len > 20) {
                    len = 20;
                }

            $(this).css("position", "absolute");
            $(this).css("zIndex", 9999);
            $(this).offset(pos);   // reset position
            $(this).attr("size", len); // open dropdown
            $(this).unbind("focus", down);
            $(this).focus();
        }
        function up() {
            $(this).css("position", "static");
            $(this).attr("size", "1");  // close dropdown
            $(this).unbind("change", up);
            $(this).focus();
        }
        $("#" + elementId).focus(down).blur(up).focus();
    }