JSFiddle - React, Tailwind, and code Playground

HTML

<span class="fraction">2|1</span>
<span class="fraction"><strike>2</strike>|1</span>

CSS

span { display: inline-block; }
.top, .bottom { display: block; }
.top { text-decoration: underline; }

JavaScript

$('.fraction').each(function() {
  var split = $(this).html().split("|");
  if (split.length === 2) {
    $(this).html('<span class="top">' + split[0] + '</span><span class="bottom">' + split[1] + '</span>');
  }
});