readability-smoothscrolling.js

readability.article.smoothScrolling = {
    reversePageScroll : false, // If they hold shift and hit space, scroll up

    /**
     * How long it takes to scroll the page, in ms.
    **/
    scrollSpeed: 500,

    /**
     * The scrollable element, which changes depending on browser. Initialized via initScrollable.
    **/
    scrollable: null,

    /**
     * initScrollable - detect which element to use for scrolling - html or body. Sets the scrollable attribute.
     *
     * Derived from getScrollable, borrowed from jQuery Smooth Scroll by Karl Swedberg:
     * https://github.com/kswedberg/jquery-smooth-scroll/blob/master/jquery.smooth-scroll.js
     *
     * @param els an array of elements to try to scroll upon - probably ['html','body']
     * @return null
    **/
    initScrollable: function(els) {
        var i = 0, scrolled = false;

        for(i=0, il=els.length; i<il; i++) {
            var tagName = els[i],
                el      = $(tagName);

            if (el.scrollTop() > 0) {
                readability.article.smoothScrolling.scrollable = el.get(0);
                break;
            }

            el.scrollTop(1);
            scrolled = el.scrollTop() > 0;
            el.scrollTop(0);

            if (scrolled) {
                readability.article.smoothScrolling.scrollable = el.get(0);
                break;
            }
        }

        // If we weren't able to initialize the scrollable at all, fall back to 'html, body'.
        if(readability.article.smoothScrolling.scrollable === null) {
            readability.article.smoothScrolling.scrollable = $('html, body');
        }
    },

    /**
     * Initialize the smooth scrolling functionality.
     * @return null
    **/
    init: function() {
        readability.article.smoothScrolling.initScrollable(['html','body']);
        
        $(document).keydown( function(e) {
            var code           = (window.event) ? event.keyCode : e.keyCode,
                viewportHeight = $(window).height(),
                offset         = $(window).scrollTop(),
                direction      = 1,
                delta          = viewportHeight - 50;

            if (code === 16) {
                readability.article.smoothScrolling.reversePageScroll = true;
                return;
            }

            if (code === 32) {
                direction = (readability.article.smoothScrolling.reversePageScroll) ? -1 : 1; 

                if(direction === 1) {
                    $('#scroll-bullet').css({'top': offset + (delta * direction), 'left': $('#rdb-article-content').position().left - 25}).show();                    
                }

                $(readability.article.smoothScrolling.scrollable).animate({scrollTop: offset + (delta * direction)}, readability.article.smoothScrolling.scrollSpeed, function () {
                    $('#scroll-bullet').delay(500).fadeOut('fast');
                });
                
                return false;
            }
        });
        
        $(document).keyup( function(e) {
            var code = (window.event) ? event.keyCode : e.keyCode;
            
            if(code === 16) {
                readability.article.smoothScrolling.reversePageScroll = false;
                return;
            }
        });
    }

};