JSFiddle - React, Tailwind, and code Playground

HTML

<select id="dropdown">
  <option value="Red">Red</option>
  <option value="Green">Green</option>
  <option value="Blue">Blue</option>
</select>
<br>
<button id="fire" type="button">Show dropdown items</button>

CSS

#dropdown {
  display: none;
}

#dropdown.show {
  display: inline-block;
}

JavaScript

function open(elem) {
    if (document.createEvent) {
        var e = document.createEvent("MouseEvents");
        e.initMouseEvent("mousedown", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
        elem[0].dispatchEvent(e);
    } else if (element.fireEvent) {
        elem[0].fireEvent("onmousedown");
    }
}

$(document).ready(function(){

	$('#fire').click(function(event){
		event.preventDefault();
		event.stopImmediatePropagation();
		$(this).blur();
		$('#dropdown').addClass("show").focus();
		open( $('#dropdown') );
	});

	$('#dropdown').blur(function(){
		$(this).removeClass('show');
	});

});