sticky navbar for bootstrap from twitter

sticky_navbar.js

// sticky navbar
  $(document).scroll(function(){
	    // If has not activated (has no attribute "data-top"
	    if (!$('.subnav').attr('data-top')) {
	        // If already fixed, then do nothing
	        if ($('.subnav').hasClass('subnav-fixed-top')) return;
	        // Remember top position
	        var offset = $('.subnav').offset()
	        $('.subnav').attr('data-top', offset.top);
	    }

	    if ($('.subnav').attr('data-top') - $('.subnav').outerHeight() <= $(this).scrollTop())
	        $('.subnav').addClass('subnav-fixed-top');
	    else
	        $('.subnav').removeClass('subnav-fixed-top');
	});