JSFiddle - React, Tailwind, and code Playground

HTML

<div class="comments">comment 1** isgood**</div>
<div class="comments">comment 2**isbad**</div>

JavaScript

function markdown(markdownable) {

var bold = /\*\*(\S(.*?\S)?)\*\*/gm;
    markdownable = markdownable.replace( bold, '<span style="font-weight:bold">$1</span>' );
    
    return markdownable;
}

$('.comments').each(function() {

    var markdownable = $(this).html(),
        comments = markdown(markdownable);
    
    $(this).html(comments);

    
});