JSFiddle - React, Tailwind, and code Playground

HTML

<div id="text">
    <h1>Lorem ipsum dolor sit amet</h1>
    <p>consectetur adipisicing elit</p>
    <p>sed do eiusmod tempor <b>incididunt</b> ut labore et dolore magna aliqua.</p>
<p>Ut enim ad minim veniam</p>
</div>

JavaScript

$("#text *").contents().filter(function() {
    return this.nodeType == 3
}).replaceWith(function() {
    return this.nodeValue.replace(/\b(\w+)\b/g, "<u>$1</u>")
});