Textarea Autoheight

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<textarea placeholder="Test Me"></textarea>

CSS

textarea {
  resize: none;
  font-size: 13px;
  padding: 10px;
  height:38px;
  min-height: 38px;
  width: 400px;
  box-sizing: border-box;
  overflow: hidden;
}

JavaScript

$('textarea').on('input', function() {

var oldHeight = $(this).outerHeight(); 
$(this).outerHeight(38);
var newHeight = this.scrollHeight + 38;
$(this).outerHeight(oldHeight);

if (newHeight !== oldHeight) 
  $(this).animate({height: newHeight}, 80);
  
});