JSFiddle - React, Tailwind, and code Playground

HTML

<p><b><u>Object replacement</u></b></h2>
<p>Line1: <span class="class1">Hello World</span></p>
<p>Line2: <span class="class1">This is a class</span></p>
<p>Line3: <span class="class2">So is this</span></p>
<p>Line4: <span class="class1">Replace me</span></p>
<br />
<p><b><u>String replacement</u></b></h2>
<p>Line1: <span class="class3">String Hello World</span></p>
<p>Line2: <span class="class3">String This is a class</span></p>
<p>Line3: <span class="class4">String So is this</span></p>
<p>Line4: <span class="class3">String Replace me</span></p>

JavaScript

$(function () {
    $('.class1').replaceWith($('<span class="class1">Foo</span>'));
    $('.class3').replaceWith($('<span class="class1">Foo</span>'));
});