JSFiddle - React, Tailwind, and code Playground

HTML

<pre></pre>

JavaScript

function femtoProtection(post) {
  //return post; // uncomment to see behavior without protection
  return post.replace(/</gi, '(');
}

function attack(post) {
	$('pre').html(femtoProtection(post));
}

attack('</pre><img src=https://pbs.twimg.com/profile_images/638751551457103872/KN-NzuRl.png>');