JSFiddle - React, Tailwind, and code Playground

HTML

<button>inserir novo script no body</button>
<div id="video" class="UJAwNkhbYWM"></div>
<iframe width="854" height="510" ID="caixa" frameborder="0" allowfullscreen></iframe>
<div id="novoScript"></div>

JavaScript

var video = $("#video").attr('class');
$('#caixa').attr('src', "https://www.youtube.com/embed/" + video);


var scriptString = "var video = 'uT3SBzmDxGk';$('#caixa').attr('src', 'https://www.youtube.com/embed/' + video);";
var script = document.createElement('script');
script = $(script).append(scriptString);

$('button').on('click', function () {
    $('#novoScript').html(script);
});