JSFiddle - React, Tailwind, and code Playground
HTML
<h2>We have cows on our farm</h2>
CSS
span { color: red}
JavaScript
var str1 = "cows"
var re = new RegExp(str1, "g");
$("h2:contains('cow')").html(function(_, html) {
return html.replace(re, '<span class="smallcaps">$1</span>')
});