JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
sdfsdsdfsdfsdf a@a.com sdfsdfsdfsdfsdfsdf
</div>

JavaScript

var page_content = document.getElementById('main').innerHTML;
var email = page_content.match(/([a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9._-]+)/gi);
var save_email = "<div class='email_tmp'> found_email <span>SAVE EMAIL</span></div>";
var result = page_content.replace(email, save_email);
document.getElementById('main').innerHTML = result;