JSFiddle - React, Tailwind, and code Playground

HTML

<div id="content-area">
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</div>
<br />
<div id="show-text"></div>

CSS

#content-area{padding:10px;border:1px dashed #f00;}
#show-text{color:#f00;}

JavaScript

function getSelected() {
  if(window.getSelection) { return window.getSelection(); }
  else if(document.getSelection) { return document.getSelection(); }
  else {
    var selection = document.selection && document.selection.createRange();
    if(selection.text) { return selection.text; }
    return false;
  }
  return false;
}
$(document).ready(function() {
  $('#content-area').mouseup(function() {
    var selection = getSelected();
    if(selection && (selection = new String(selection).replace(/^\s+|\s+$/g,''))) {
        $('#show-text').html(selection)
    }
  });
});