jQuery sidebar scrolling with the window implementation method_jquery

$(function() {
    var $sidebar   = $("#sidebar"),  
        $window    = $(window),  
        offset     = $sidebar.offset(),  
        topPadding = 15;  

    $window.scroll(function() {  
        if ($window.scrollTop() > offset.top) {  
            $sidebar.stop().animate({  
                marginTop: $window.scrollTop() - offset.top topPadding  
            });  
        } else {  
            $sidebar.stop().animate({  
                marginTop: 0  
            });  
        }  
    });  

});