JSFiddle - React, Tailwind, and code Playground

JavaScript

var ftsPopup = window.open();
var $ftsPopup = $(ftsPopup.document.body).addClass('hello'); // works
alert('addClass worked');

var el = ftsPopup.document.createElement('div');
$(el).html('The cake is a lie').appendTo($ftsPopup); // works
alert('appendTo cake worked');

$('<div>Hello World</div>').appendTo($ftsPopup); // fails
alert('appendTo hello worked');