jQuery Smooth Scrolling

HTML

<html>

    <body>
        <a href="#bottom" id="top">nach unten</a>
        <p>hier</p>
        <p>funktioniert</p>
        <p>es</p>
        <a href="#top" id="bottom">nach oben</a>
    </body>

</html>

CSS

html {
    font-size: 20px;
    text-align: center;
}

p {
    padding: 200px 0;
}

JavaScript

$(document).ready(function() {
      $('a[href^="#"]').on('click', function(e) {
          e.preventDefault();

          var target = this.hash;
          var $target = $(target);

          $('html, body').stop().animate({
              'scrollTop': $target.offset().top
          }, 900, 'swing', function() {
              window.location.hash = target;
          });
      });
  });