JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="textareaId">
    test
    test
    test
    test
</textarea>
<input type="button" value="Test" />

JavaScript

function isTextSelected(input){
   var startPos = input.selectionStart;
   var endPos = input.selectionEnd;
   var doc = document.selection;

   if(doc && doc.createRange().text.length != 0){
      return true;
   }else if (!doc && input.value.substring(startPos,endPos).length != 0){
      return true;
   }
   return false;
}

$('input').click(function(){
   
   if(isTextSelected($('#textareaId')[0])){
      alert('Text selected');
   } 
});