JSFiddle - React, Tailwind, and code Playground

HTML

<div class="col-md-12">
  erge
</div>
<div class="col-md-4">
  rwger
</div>
<div class="col-md-9">
  wrgwerg
</div>

JavaScript

$("[class^=col-md-]").attr("class", "col-md-6");