JSFiddle - React, Tailwind, and code Playground

HTML

<textarea></textarea>
<div></div><button type="button">Markdownify</button>

JavaScript

$(document.body).on('click', 'button', function() {

    var val=$('textarea').val();
    
    var bolded=val.replace(/\x2a\x2a[A-z0-9]+\x2a\x2a/gi, '<span style="font-weight:bold;">"'+val+'"</span>');
    
    $('div').html(bolded);
});