Sample code for adding/removing css class names according to a user's scrolling position on the page. example result is to change the background color of navigational items. $j for use with jQuery.noConflict();

scrollSwitch.js

   $j(window).scroll(function(){
     $navp = $j('#mm-nav'); 
     $nav = $j('#mm-nav li a');

     $navp = $j('#mm-nav'); 
     $nav = $j('#mm-nav li a');
     
     for(var i=1; i<8; i++) {
        var os = i === 7 ? 190 : 90;
        
          if($j(this).scrollTop() >= $j('.p'+i).offset().top - os) {
                $nav.removeClass("sel");
                $j('#mm-nav #a'+i ).addClass("sel");
            }
     }
   

   if ($j(this).scrollTop() > 250 && $navp.css('position') != 'fixed'){ 
       $navp.addClass("fixedhead"); 
     } else if ($j(this).scrollTop() < 250 && $navp.css('position') == 'fixed'){ 
       $navp.removeClass("fixedhead"); 
     }