MAGETWO-66300: [GitHub][PR] Stickyjs improvements #7139

 - Merge Pull Request #7139 from vovayatsyuk/magento2:improvements-stickyjs
 - Merged commits:
   1. 8bfa048
   2. 996d213
   3. a7254cf
   4. 798469a
   5. 9f926ef
   6. c6d309b
   7. 766292c
   8. 0e479a3
   9. ae7f764
   10. dde585c
   11. 5071e54
   12. e6795cb
   13. 7ae6be0
   14. db648a6
   15. fc0ae57
   16. febbd88
   17. d715b42
   18. 62b822c

Author: Oleksii Korshenko

lib/web/mage/sticky.js

@@ -11,7 +11,48 @@ define([
 
     $.widget('mage.sticky', {
         options: {
-            container: ''
+            /**
+             * Element selector, who's height will be used to restrict the
+             * maximum offsetTop position of the stuck element.
+             * Default uses document body.
+             * @type {String}
+             */
+            container: '',
+
+            /**
+             * Spacing in pixels above the stuck element
+             * @type {Number|Function} Number or Function that will return a Number
+             */
+            spacingTop: 0,
+
+            /**
+             * Allows postponing sticking, until element will go out of the
+             * screen for the number of pixels.
+             * @type {Number|Function} Number or Function that will return a Number
+             */
+            stickAfter: 0,
+
+            /**
+             * CSS class for active sticky state
+             * @type {String}
+             */
+            stickyClass: '_sticky'
+        },
+
+        /**
+         * Retrieve option value
+         * @param  {String} option
+         * @return {*}
+         * @private
+         */
+        _getOptionValue: function (option) {
+            var value = this.options[option] || 0;
+
+            if (typeof value === 'function') {
+                value = this.options[option]();
+            }
+
+            return value;
         },
 
         /**
@@ -35,14 +76,29 @@ define([
          */
         _stick: function () {
             var offset,
-                isStatic;
+                isStatic,
+                stuck,
+                stickAfter;
 
             isStatic = this.element.css('position') === 'static';
 
             if (!isStatic && this.element.is(':visible')) {
-                offset = $(document).scrollTop() - this.parentOffset;
+                offset = $(document).scrollTop() -
+                    this.parentOffset +
+                    this._getOptionValue('spacingTop');
+
                 offset = Math.max(0, Math.min(offset, this.maxOffset));
-                this.element.css('top', offset);
+
+                stuck = this.element.hasClass(this.options.stickyClass);
+                stickAfter = this._getOptionValue('stickAfter');
+
+                if (offset && !stuck && offset < stickAfter) {
+                    offset = 0;
+                }
+
+                this.element
+                    .toggleClass(this.options.stickyClass, offset > 0)
+                    .css('top', offset);
             }
         },