https://www.chesbay.us/library/public/designs/sticky/jquery-sticky.js

1// Sticky Plugin v1.0.3 for jQuery
2// =============
3// Author: Anthony Garand
4// Improvements by German M. Bravo (Kronuz) and Ruud Kamphuis (ruudk)
5// Improvements by Leonardo C. Daronco (daronco)
6// Created: 02/14/2011
7// Date: 07/20/2015
8// Website: http://stickyjs.com/
9// Description: Makes an element on the page stick on the screen as you scroll
10//              It will only set the 'top' and 'position' of your element, you
11//              might need to adjust the width in some cases.
12
13(function (factory) {
14    if (typeof define === 'function' && define.amd) {
15        // AMD. Register as an anonymous module.
16        define(['jquery'], factory);
17    } else if (typeof module === 'object' && module.exports) {
18        // Node/CommonJS
19        module.exports = factory(require('jquery'));
20    } else {
21        // Browser globals
22        factory(jQuery);
23    }
24}(function ($) {
25    var slice = Array.prototype.slice; // save ref to original slice()
26    var splice = Array.prototype.splice; // save ref to original slice()
27
28  var defaults = {
29      topSpacing: 0,
30      bottomSpacing: 0,
31      className: 'is-sticky',
32      wrapperClassName: 'sticky-wrapper',
33      center: false,
34      getWidthFrom: '',
35      widthFromWrapper: true, // works only when .getWidthFrom is empty
36      responsiveWidth: false
37    },
38    $window = $(window),
39    $document = $(document),
40    sticked = [],
41    windowHeight = $window.height(),
42    scroller = function() {
43      var scrollTop = $window.scrollTop(),
44        documentHeight = $document.height(),
45        dwh = documentHeight - windowHeight,
46        extra = (scrollTop > dwh) ? dwh - scrollTop : 0;
47
48      for (var i = 0, l = sticked.length; i < l; i++) {
49        var s = sticked[i],
50          elementTop = s.stickyWrapper.offset().top,
51          etse = elementTop - s.topSpacing - extra;
52
53        //update height in case of dynamic content
54        s.stickyWrapper.css('height', s.stickyElement.outerHeight());
55
56        if (scrollTop <= etse) {
57          if (s.currentTop !== null) {
58            s.stickyElement
59              .css({
60                'width': '',
61                'position': '',
62                'top': ''
63              });
64            s.stickyElement.parent().removeClass(s.className);
65            s.stickyElement.trigger('sticky-end', [s]);
66            s.currentTop = null;
67          }
68        }
69        else {
70          var newTop = documentHeight - s.stickyElement.outerHeight()
71            - s.topSpacing - s.bottomSpacing - scrollTop - extra;
72          if (newTop < 0) {
73            newTop = newTop + s.topSpacing;
74          } else {
75            newTop = s.topSpacing;
76          }
77          if (s.currentTop !== newTop) {
78            var newWidth;
79            if (s.getWidthFrom) {
80                newWidth = $(s.getWidthFrom).width() || null;
81            } else if (s.widthFromWrapper) {
82                newWidth = s.stickyWrapper.width();
83            }
84            if (newWidth == null) {
85                newWidth = s.stickyElement.width();
86            }
87            s.stickyElement
88              .css('width', newWidth)
89              .css('position', 'fixed')
90              .css('top', newTop);
91
92            s.stickyElement.parent().addClass(s.className);
93
94            if (s.currentTop === null) {
95              s.stickyElement.trigger('sticky-start', [s]);
96            } else {
97              // sticky is started but it have to be repositioned
98              s.stickyElement.trigger('sticky-update', [s]);
99            }
100
101            if (s.currentTop === s.topSpacing && s.currentTop > newTop || s.currentTop === null && newTop < s.topSpacing) {
102              // just reached bottom || just started to stick but bottom is already reached
103              s.stickyElement.trigger('sticky-bottom-reached', [s]);
104            } else if(s.currentTop !== null && newTop === s.topSpacing && s.currentTop < newTop) {
105              // sticky is started && sticked at topSpacing && overflowing from top just finished
106              s.stickyElement.trigger('sticky-bottom-unreached', [s]);
107            }
108
109            s.currentTop = newTop;
110          }
111
112          // Check if sticky has reached end of container and stop sticking
113          var stickyWrapperContainer = s.stickyWrapper.parent();
114          var unstick = (s.stickyElement.offset().top + s.stickyElement.outerHeight() >= stickyWrapperContainer.offset().top + stickyWrapperContainer.outerHeight()) && (s.stickyElement.offset().top <= s.topSpacing);
115
116          if( unstick ) {
117            s.stickyElement
118              .css('position', 'absolute')
119              .css('top', '')
120              .css('bottom', 0);
121          } else {
122            s.stickyElement
123              .css('position', 'fixed')
124              .css('top', newTop)
125              .css('bottom', '');
126          }
127        }
128      }
129    },
130    resizer = function() {
131      windowHeight = $window.height();
132
133      for (var i = 0, l = sticked.length; i < l; i++) {
134        var s = sticked[i];
135        var newWidth = null;
136        if (s.getWidthFrom) {
137            if (s.responsiveWidth) {
138                newWidth = $(s.getWidthFrom).width();
139            }
140        } else if(s.widthFromWrapper) {
141            newWidth = s.stickyWrapper.width();
142        }
143        if (newWidth != null) {
144            s.stickyElement.css('width', newWidth);
145        }
146      }
147    },
148    methods = {
149      init: function(options) {
150        var o = $.extend({}, defaults, options);
151        return this.each(function() {
152          var stickyElement = $(this);
153
154          var stickyId = stickyElement.attr('id');
155          var wrapperId = stickyId ? stickyId + '-' + defaults.wrapperClassName : defaults.wrapperClassName;
156          var wrapper = $('<div></div>')
157            .attr('id', wrapperId)
158            .addClass(o.wrapperClassName);
159
160          stickyElement.wrapAll(wrapper);
161
162          var stickyWrapper = stickyElement.parent();
163
164          if (o.center) {
165            stickyWrapper.css({width:stickyElement.outerWidth(),marginLeft:"auto",marginRight:"auto"});
166          }
167
168          if (stickyElement.css("float") === "right") {
169            stickyElement.css({"float":"none"}).parent().css({"float":"right"});
170          }
171
172          o.stickyElement = stickyElement;
173          o.stickyWrapper = stickyWrapper;
174          o.currentTop    = null;
175
176          sticked.push(o);
177
178          methods.setWrapperHeight(this);
179          methods.setupChangeListeners(this);
180        });
181      },
182
183      setWrapperHeight: function(stickyElement) {
184        var element = $(stickyElement);
185        var stickyWrapper = element.parent();
186        if (stickyWrapper) {
187          stickyWrapper.css('height', element.outerHeight());
188        }
189      },
190
191      setupChangeListeners: function(stickyElement) {
192        if (window.MutationObserver) {
193          var mutationObserver = new window.MutationObserver(function(mutations) {
194            if (mutations[0].addedNodes.length || mutations[0].removedNodes.length) {
195              methods.setWrapperHeight(stickyElement);
196            }
197          });
198          mutationObserver.observe(stickyElement, {subtree: true, childList: true});
199        } else {
200          stickyElement.addEventListener('DOMNodeInserted', function() {
201            methods.setWrapperHeight(stickyElement);
202          }, false);
203          stickyElement.addEventListener('DOMNodeRemoved', function() {
204            methods.setWrapperHeight(stickyElement);
205          }, false);
206        }
207      },
208      update: scroller,
209      unstick: function(options) {
210        return this.each(function() {
211          var that = this;
212          var unstickyElement = $(that);
213
214          var removeIdx = -1;
215          var i = sticked.length;
216          while (i-- > 0) {
217            if (sticked[i].stickyElement.get(0) === that) {
218                splice.call(sticked,i,1);
219                removeIdx = i;
220            }
221          }
222          if(removeIdx !== -1) {
223            unstickyElement.unwrap();
224            unstickyElement
225              .css({
226                'width': '',
227                'position': '',
228                'top': '',
229                'float': ''
230              })
231            ;
232          }
233        });
234      }
235    };
236
237  // should be more efficient than using $window.scroll(scroller) and $window.resize(resizer):
238  if (window.addEventListener) {
239    window.addEventListener('scroll', scroller, false);
240    window.addEventListener('resize', resizer, false);
241  } else if (window.attachEvent) {
242    window.attachEvent('onscroll', scroller);
243    window.attachEvent('onresize', resizer);
244  }
245
246  $.fn.sticky = function(method) {
247    if (methods[method]) {
248      return methods[method].apply(this, slice.call(arguments, 1));
249    } else if (typeof method === 'object' || !method ) {
250      return methods.init.apply( this, arguments );
251    } else {
252      $.error('Method ' + method + ' does not exist on jQuery.sticky');
253    }
254  };
255
256  $.fn.unstick = function(method) {
257    if (methods[method]) {
258      return methods[method].apply(this, slice.call(arguments, 1));
259    } else if (typeof method === 'object' || !method ) {
260      return methods.unstick.apply( this, arguments );
261    } else {
262      $.error('Method ' + method + ' does not exist on jQuery.sticky');
263    }
264  };
265  $(function() {
266    setTimeout(scroller, 0);
267  });
268}));