JSFiddle - React, Tailwind, and code Playground

HTML

<BODY>
    <TEXTAREA cols="40" rows="10" onselect="alert(GetText());">
      Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diem nonummy 
      nibh euismod tincidunt ut lacreet dolore magna aliguam erat volutpat. 
      Ut wisis enim ad minim veniam, quis nostrud exerci tution ullamcorper 
      suscipit lobortis nisl ut aliquip ex ea commodo consequat. 
    </TEXTAREA>
  </BODY>

JavaScript

GetText = function() {
  if (window.getSelection) {
    return window.getSelection();
  }
  else 
    if (document.getSelection) {
      return document.getSelection();
    }
    else
      if (document.selection) {
        return document.selection.createRange().text;
      } 
}