jquery.ba-floatingscrollbar.js

/*!
 * jQuery Floating Scrollbar - v0.3 - 02/27/2011
 * http://benalman.com/
 * 
 * Copyright (c) 2011 "Cowboy" Ben Alman
 * Dual licensed under the MIT and GPL licenses.
 * http://benalman.com/about/license/
 */

(function($){
  var // A few reused jQuery objects.
      win = $(this),
      html = $('html'),

      // All the elements being monitored.
      elems = $([]),

      // The current element.
      current,

      // The previous current element.
      previous,

      // Create the floating scrollbar.
      scroller = $('<div id="floating-scrollbar"><div/></div>'),
      scrollerInner = scroller.children();

  // Initialize the floating scrollbar.
  scroller
    .hide()
    .css({
      position: 'fixed',
      bottom: 0,
      height: '30px',
      overflowX: 'auto',
      overflowY: 'hidden'
    })
    .scroll(function() {
      // If there's a current element, set its scroll appropriately.
      current && current.scrollLeft(scroller.scrollLeft())
    });
    
  scrollerInner.css({
    border: '1px solid #fff',
    opacity: 0.01
  });

  // Call on elements to monitor their position and scrollness. Pass `false` to
  // stop monitoring those elements.
  $.fn.floatingScrollbar = function( state ) {
    if ( state === false ) {
      // Remove these elements from the list.
      elems = elems.not(this);
      // Stop monitoring elements for scroll.
      this.unbind('scroll', scrollCurrent);
      if ( !elems.length ) {
        // No elements remain, so detach scroller and unbind events.
        scroller.detach();
        win.unbind('resize scroll', update);
      }
    } else if ( this.length ) {
      // Don't assume the set is non-empty!
      if ( !elems.length ) {
        // Adding elements for the first time, so attach scroller and bind
        // events.
        scroller.appendTo('body');
        win.resize(update).scroll(update);
      }
      // Add these elements to the list.
      elems = elems.add(this);
    }
    // Update.
    update();
    // Make chainable.
    return this;
  };

  // Call this to force an update, for instance, if elements were inserted into
  // the DOM before monitored elements, changing their vertical position.
  $.floatingScrollbarUpdate = update;

  // Hide or show the floating scrollbar.
  function setState( state ) {
    scroller.toggle(!!state);
  }

  // Sync floating scrollbar if element content is scrolled.
  function scrollCurrent() {
    current && scroller.scrollLeft(current.scrollLeft())
  }

  // This is called on window scroll or resize, or when elements are added or
  // removed from the internal elems list.
  function update() {
    previous = current;
    current = null;

    // Find the first element whose content is visible, but whose bottom is
    // below the viewport.
    elems.each(function(){
      var elem = $(this),
          top = elem.offset().top,
          bottom = top + elem.height(),
          viewportBottom = win.scrollTop() + win.height(),
          topOffset = 30;

      if ( top + topOffset < viewportBottom && bottom > viewportBottom ) {
        current = elem;
        return false;
      }
    });

    // Abort if no elements were found.
    if ( !current ) { setState(); return; }

    // Test to see if the current element has a scrollbar.
    var scroll = current.scrollLeft();
    
    var scrollbarWidth = jQuery(current[0]).find("table")[0].clientWidth - current[0].clientWidth;
    current.scrollLeft(scroll);

    // Abort if the element doesn't have a scrollbar.
    if ( scrollbarWidth <= 0 ) { setState(); return; }

    // Show the floating scrollbar.
    setState(true);
    
    // Adjust the floating scrollbar as-necessary.
    scroller
      .css({
        left: current.offset().left,
        width: current[0].clientWidth
      }).scrollLeft(scroll);
    
    scrollerInner.width(current[0].offsetWidth + scrollbarWidth);

    // Sync floating scrollbar if element content is scrolled.
    if ( current !== previous ) {
      previous && previous.unbind('scroll', scrollCurrent);
      current.scroll(scrollCurrent);
    }
  }

})(jQuery);