JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset disabled>
    <input id="fieldset_child" type="text" value="Inherit Disabled" />
</fieldset>

JavaScript

// IE 9-11
console.log(document.querySelectorAll('#fieldset_child:disabled').length);

// jQuery's "polyfill" for :disabled is to just look at the prop
console.log(document.getElementById('fieldset_child').disabled);