JSFiddle - React, Tailwind, and code Playground
HTML
<textarea id="textArea"><span style="color: blue">Test</span></textarea><br />
Show textarea here: <span id="show"></span>
JavaScript
var textWOHTML = $("textarea").val().replace(/<(.|\n)*?>/, '').replace(/<\/(.|\n)*?>/, '');
var textWithHTML = $("textarea").val();
$('#textArea').val(textWOHTML);
$("#show").html(textWithHTML);