GitHub - Octobiwan - SpeederFloating.js

/*
    This little code move the speeder on the 404 error page of GitHub.
    For a demo :
    * Copy the code below with Ctrl+C.
    * Find a 404 error page (like this one: "https://github.com/@").
    * Paste the code in the address bar.
    * Add "javascript:" at the beginning of the code.
    * Press enter, enjoy! :D
    --
    I don't use the argument (number) "progress" of jQuery in the progress callback,
    because this number goes from 0 to 1 linearly but not easingly...
*/

(function(){
    var $speeder = jQuery('#parallax_speeder'),
        $shad    = jQuery('#parallax_speedershadow'),
        shadH    = $shad.height(),
        dur      = 2500,
        up       = -25;
    function shadCSS(){
        var p = parseInt($speeder.css('marginTop')) / up;
        $shad.css('height',  (shadH - up * p) + 'px');
        $shad.css('opacity', 1 - p / 2);
    }
    function speederB(){$speeder.animate({marginTop:  '0px'},{duration:dur,progress:shadCSS,complete:speederA})}
    function speederA(){$speeder.animate({marginTop:up+'px'},{duration:dur,progress:shadCSS,complete:speederB})}
    speederA();
})();