Edit in JSFiddle

$('a[href=#top]').click(function(){
    $('html, body').animate({scrollTop:0}, 'slow');
    return false;
});

<a name="top"></a>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<p>===</p>
<p>----------------------</p>
<p>scroll to bottom of the page and click the "back to top" link</p>
<a href="#top">back to top</a>