input event with if condition

I use eventlistener to detect the rows in textarea, but when I press backspace the if condition doesn’t work. How can I improve this?

$('textarea').on('input', function() {
  // Get the scroll height of the textarea
  let taHeight = $('textarea').scrollHeight;
  let numberOfLines = Math.floor(taHeight / 16);
  height(numberOfLines);

})

function height(numberOfLines) {
  console.log(numberOfLines);
  if (numberOfLines == 2) {
    $('textarea').removeClass('row-2 row-3').addClass('row-2');
  } else if (numberOfLines == 3) {
    $('textarea').removeClass('row-2 row-3').addClass('row-3');
  } else {
    $('textarea').removeClass('row-2 row-3');
  }
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<textarea></textarea>