Try this
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;
}
Usage 
if(isTextSelected($('#textareaId')[0])){
   //text selected
}
Demo