JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

<ul><li style="display:none;"></ul>

JavaScript

function isDefaultVisible(el) {
    var el = document.createElement(el.tagName);
    return window.getComputedStyle(el,null).getPropertyValue('display') != 'none';
}
// TEST
var el = document.getElementsByTagName('li').item(0); // enter an existing tag name here
alert(isDefaultVisible(el))