jquery.jsticky.js

/* jSticky Plugin
 * =============
 * Author: Andrew Henderson (@AndrewHenderson)
 * Contributor: Mike Street (@mikestreety)
 * Date: 9/7/2012
 * Update: 09/20/2016
 * Website: http://github.com/andrewhenderson/jsticky/
 * Description: A jQuery plugin that keeps select DOM
 * element(s) in view while scrolling the page.
 */

;(function($) {

  $.fn.sticky = function(options) {
    var defaults = {
      topSpacing: 0, // No spacing by default
      zIndex: '', // No default z-index
      stopper: '.sticky-stopper', // Default stopper class, also accepts number value
      stickyClass: false // Class applied to element when it's stuck
    };
    var settings = $.extend({}, defaults, options); // Accepts custom stopper id or class

    // Checks if custom z-index was defined
    function checkIndex() {
      if (typeof settings.zIndex == 'number') {
        return true;
      } else {
        return false;
      }
    }

    var hasIndex = checkIndex(); // True or false

    // Checks if a stopper exists in the DOM or number defined
    function checkStopper() {
      if (0 < $(settings.stopper).length || typeof settings.stopper === 'number') {
        return true;
      } else {
        return false;
      }
    }
    var hasStopper = checkStopper(); // True or false

    return this.each(function() {

      var $this = $(this);
      var thisHeight = $this.outerHeight();
      var thisWidth = $this.outerWidth();
      var topSpacing = settings.topSpacing;
      var zIndex = settings.zIndex;
      var pushPoint = $this.offset().top - topSpacing; // Point at which the sticky element starts pushing
      var placeholder = $('<div></div>').width(thisWidth).height(thisHeight).addClass('sticky-placeholder'); // Cache a clone sticky element
      var stopper = settings.stopper;
      var $window = $(window);

      function stickyScroll() {

        var windowTop  = $window.scrollTop(); // Check window's scroll position
        var stopPoint = stopper;
        var parentWidth = $this.parent().width();

        placeholder.width(parentWidth)

        if ( hasStopper && typeof stopper === 'string' ) {
          var stopperTop = $(stopper).offset().top;
          stopPoint  = (stopperTop - thisHeight) - topSpacing;
        }

        if (pushPoint < windowTop) {
          // Create a placeholder for sticky element to occupy vertical real estate
          if(settings.stickyClass)
            $this.addClass(settings.stickyClass);

          $this.after(placeholder).css({
            position: 'fixed',
            top: topSpacing,
            width: parentWidth
          });

          if (hasIndex) {
            $this.css({
              zIndex: zIndex
            });
          }

          if (hasStopper) {
            if (stopPoint < windowTop) {
              var diff = (stopPoint - windowTop) + topSpacing;
              $this.css({
                top: diff
              });
            }
          }
        } else {
          if(settings.stickyClass)
            $this.removeClass(settings.stickyClass);

          $this.css({
            position: 'static',
            top: null,
            left: null,
            width: 'auto'
          });

          placeholder.remove();
        }
      }

      if($window.innerHeight() > thisHeight) {

        $window.bind('scroll', stickyScroll);
        $window.bind('load', stickyScroll);
        $window.bind('resize', stickyScroll);
      }
    });
  };
})(jQuery);