JSFiddle - React, Tailwind, and code Playground

HTML

<div data-role="page">
  <div data-role="popup" id="signupPopup">
    <h3 class="centerText">Login</h3>
  </div>
  Page
</div>

JavaScript

$(document).bind('pagecreate', function() {
    $("#signupPopup").popup('open');
});