JSFiddle - React, Tailwind, and code Playground

HTML

<select id="testDropDown">
    <option value="">TEST</option>
    <option value="http://www.google.com">Google</option>
    <option value="http://stackoverflow.com/">Stack</option>
    <option value="https://developer.mozilla.org/en-US/">MDN</option>
</select>
<span id="result"></span>

JavaScript

var dropdown = document.getElementById("testDropDown");
var result = document.getElementById("result");
var oldSelectedIndex = 0;

dropdown.addEventListener('click', Foo);

function Foo(e)
{
 		var selectedIndex = dropdown.selectedIndex;
    if(selectedIndex !== oldSelectedIndex)
    {
        var val = dropdown.options[selectedIndex].value;
        var opened = window.open(val);
        oldSelectedIndex = selectedIndex;
    }
}