snippet.js

var jump = $(this);
var size = jump.height();
var _min = parseInt(jump.offset().top);
var _max = jump.parent().parent().height();
var _win = $(window);

// Callback for scrolling
var callback = function()
{
	// Get the current scroll offset
	var _cur = _win.scrollTop();

	if (_cur > _max)
	{
		// Make the jump menu stay within the parent
		jump.stop().animate({ marginTop: _max - size }, 200);
	}
	else if (_cur > _min)
	{
		// Make the jump menu follow scrolling
		jump.stop().animate({ marginTop: _cur - _min }, 200);
	}
	else
	{
		// Just place the jump menu at the top
		jump.stop().css('margin-top', 0);
	}
};
var timer = null;

// Run the callback
callback();

$(window).scroll(function()
{
	// Stop the current timer
	if (timer) clearTimeout(timer);

	// Create a new timer
	setTimeout(callback, 20);
});