Prevent scrolling in scrollable containers

This prevents scrolling within scrollable containers (excluding the
dropdown) when the dropdown is open. This fixes an issue where the
dropdown would go out of sync with the parent container when the
parent container was scrolled.

We did not have this issue in past versions of Select2 because the
mask prevented any scrolling. Now that we have removed the mask, we
have to deal with scrolling from different areas of the page.

We initially tried to hook into the `scroll` events of the parent
containers, but because of a list of issues we decided against it.
If the container scrolled out of view, the dropdown would still be
left open and above everything else, even though the container
wasn't visually connected to it.

The `scroll` event does not bubble, so we need to attach the `scroll`
handler to every parent element that is scrollable. Since it is
surprisingly difficult to determine if an element is scrollable,
we modified some CC-BY-SA code and use that to determine if the
element has a scrollbar. The original `hasScroll` function can be
found at http://codereview.stackexchange.com/q/13338, the same link
left within the code, and was originally designed to be a sizzle
selector. As Select2 does not require a sizzle-compatible version of
jQuery, we converted it into a function that could be used with
`.filter` to filter down the elements.

This closes https://github.com/select2/select2/issues/2975.

dist/js/select2.amd.full.js

@@ -193,6 +193,31 @@ define(['jquery'], function ($) {define('select2/utils',[], function () {
     return data;
   };
 
+  Utils.hasScroll = function (index, el) {
+    // Adapted from the function created by @ShadowScripter
+    // and adapted by @BillBarry on the Stack Exchange Code Review website.
+    // The original code can be found at
+    // http://codereview.stackexchange.com/q/13338
+    // and was designed to be used with the Sizzle selector engine.
+
+    var $el = $(el);
+    var overflowX = el.style.overflowX;
+    var overflowY = el.style.overflowY;
+
+    //Check both x and y declarations
+    if (overflowX === overflowY &&
+        (overflowY === 'hidden' || overflowY === 'visible')) {
+      return false;
+    }
+
+    if (overflowX === 'scroll' || overflowY === 'scroll') {
+      return true;
+    }
+
+    return ($el.innerHeight() < el.scrollHeight ||
+      $el.innerWidth() < el.scrollWidth);
+  };
+
   return Utils;
 });
 
@@ -3252,8 +3277,9 @@ define('select2/dropdown/infiniteScroll',[
 });
 
 define('select2/dropdown/attachBody',[
-  'jquery'
+  'jquery',
-], function ($) {
+  '../utils'
+], function ($, Utils) {
   function AttachBody (decorated, $element, options) {
     this.$dropdownParent = options.get('dropdownParent') || document.body;
 
@@ -3333,6 +3359,19 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.each(function () {
+      $(this).data('select2-scroll-position', {
+        x: $(this).scrollLeft(),
+        y: $(this).scrollTop()
+      });
+    });
+
+    $watchers.on(scrollEvent, function (ev) {
+      var position = $(this).data('select2-scroll-position');
+      $(this).scrollTop(position.y);
+    });
+
     $(window).on(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent,
       function (e) {
       self._positionDropdown();
@@ -3345,6 +3384,9 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.off(scrollEvent);
+
     $(window).off(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent);
   };
 

dist/js/select2.amd.js

@@ -193,6 +193,31 @@ define(['jquery'], function ($) {define('select2/utils',[], function () {
     return data;
   };
 
+  Utils.hasScroll = function (index, el) {
+    // Adapted from the function created by @ShadowScripter
+    // and adapted by @BillBarry on the Stack Exchange Code Review website.
+    // The original code can be found at
+    // http://codereview.stackexchange.com/q/13338
+    // and was designed to be used with the Sizzle selector engine.
+
+    var $el = $(el);
+    var overflowX = el.style.overflowX;
+    var overflowY = el.style.overflowY;
+
+    //Check both x and y declarations
+    if (overflowX === overflowY &&
+        (overflowY === 'hidden' || overflowY === 'visible')) {
+      return false;
+    }
+
+    if (overflowX === 'scroll' || overflowY === 'scroll') {
+      return true;
+    }
+
+    return ($el.innerHeight() < el.scrollHeight ||
+      $el.innerWidth() < el.scrollWidth);
+  };
+
   return Utils;
 });
 
@@ -3252,8 +3277,9 @@ define('select2/dropdown/infiniteScroll',[
 });
 
 define('select2/dropdown/attachBody',[
-  'jquery'
+  'jquery',
-], function ($) {
+  '../utils'
+], function ($, Utils) {
   function AttachBody (decorated, $element, options) {
     this.$dropdownParent = options.get('dropdownParent') || document.body;
 
@@ -3333,6 +3359,19 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.each(function () {
+      $(this).data('select2-scroll-position', {
+        x: $(this).scrollLeft(),
+        y: $(this).scrollTop()
+      });
+    });
+
+    $watchers.on(scrollEvent, function (ev) {
+      var position = $(this).data('select2-scroll-position');
+      $(this).scrollTop(position.y);
+    });
+
     $(window).on(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent,
       function (e) {
       self._positionDropdown();
@@ -3345,6 +3384,9 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.off(scrollEvent);
+
     $(window).off(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent);
   };
 

dist/js/select2.full.js

@@ -631,6 +631,31 @@ define('select2/utils',[], function () {
     return data;
   };
 
+  Utils.hasScroll = function (index, el) {
+    // Adapted from the function created by @ShadowScripter
+    // and adapted by @BillBarry on the Stack Exchange Code Review website.
+    // The original code can be found at
+    // http://codereview.stackexchange.com/q/13338
+    // and was designed to be used with the Sizzle selector engine.
+
+    var $el = $(el);
+    var overflowX = el.style.overflowX;
+    var overflowY = el.style.overflowY;
+
+    //Check both x and y declarations
+    if (overflowX === overflowY &&
+        (overflowY === 'hidden' || overflowY === 'visible')) {
+      return false;
+    }
+
+    if (overflowX === 'scroll' || overflowY === 'scroll') {
+      return true;
+    }
+
+    return ($el.innerHeight() < el.scrollHeight ||
+      $el.innerWidth() < el.scrollWidth);
+  };
+
   return Utils;
 });
 
@@ -3690,8 +3715,9 @@ define('select2/dropdown/infiniteScroll',[
 });
 
 define('select2/dropdown/attachBody',[
-  'jquery'
+  'jquery',
-], function ($) {
+  '../utils'
+], function ($, Utils) {
   function AttachBody (decorated, $element, options) {
     this.$dropdownParent = options.get('dropdownParent') || document.body;
 
@@ -3771,6 +3797,19 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.each(function () {
+      $(this).data('select2-scroll-position', {
+        x: $(this).scrollLeft(),
+        y: $(this).scrollTop()
+      });
+    });
+
+    $watchers.on(scrollEvent, function (ev) {
+      var position = $(this).data('select2-scroll-position');
+      $(this).scrollTop(position.y);
+    });
+
     $(window).on(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent,
       function (e) {
       self._positionDropdown();
@@ -3783,6 +3822,9 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.off(scrollEvent);
+
     $(window).off(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent);
   };
 

dist/js/select2.js

@@ -631,6 +631,31 @@ define('select2/utils',[], function () {
     return data;
   };
 
+  Utils.hasScroll = function (index, el) {
+    // Adapted from the function created by @ShadowScripter
+    // and adapted by @BillBarry on the Stack Exchange Code Review website.
+    // The original code can be found at
+    // http://codereview.stackexchange.com/q/13338
+    // and was designed to be used with the Sizzle selector engine.
+
+    var $el = $(el);
+    var overflowX = el.style.overflowX;
+    var overflowY = el.style.overflowY;
+
+    //Check both x and y declarations
+    if (overflowX === overflowY &&
+        (overflowY === 'hidden' || overflowY === 'visible')) {
+      return false;
+    }
+
+    if (overflowX === 'scroll' || overflowY === 'scroll') {
+      return true;
+    }
+
+    return ($el.innerHeight() < el.scrollHeight ||
+      $el.innerWidth() < el.scrollWidth);
+  };
+
   return Utils;
 });
 
@@ -3690,8 +3715,9 @@ define('select2/dropdown/infiniteScroll',[
 });
 
 define('select2/dropdown/attachBody',[
-  'jquery'
+  'jquery',
-], function ($) {
+  '../utils'
+], function ($, Utils) {
   function AttachBody (decorated, $element, options) {
     this.$dropdownParent = options.get('dropdownParent') || document.body;
 
@@ -3771,6 +3797,19 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.each(function () {
+      $(this).data('select2-scroll-position', {
+        x: $(this).scrollLeft(),
+        y: $(this).scrollTop()
+      });
+    });
+
+    $watchers.on(scrollEvent, function (ev) {
+      var position = $(this).data('select2-scroll-position');
+      $(this).scrollTop(position.y);
+    });
+
     $(window).on(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent,
       function (e) {
       self._positionDropdown();
@@ -3783,6 +3822,9 @@ define('select2/dropdown/attachBody',[
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.off(scrollEvent);
+
     $(window).off(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent);
   };
 

src/js/select2/dropdown/attachBody.js

@@ -1,6 +1,7 @@
 define([
-  'jquery'
+  'jquery',
-], function ($) {
+  '../utils'
+], function ($, Utils) {
   function AttachBody (decorated, $element, options) {
     this.$dropdownParent = options.get('dropdownParent') || document.body;
 
@@ -80,6 +81,19 @@ define([
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.each(function () {
+      $(this).data('select2-scroll-position', {
+        x: $(this).scrollLeft(),
+        y: $(this).scrollTop()
+      });
+    });
+
+    $watchers.on(scrollEvent, function (ev) {
+      var position = $(this).data('select2-scroll-position');
+      $(this).scrollTop(position.y);
+    });
+
     $(window).on(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent,
       function (e) {
       self._positionDropdown();
@@ -92,6 +106,9 @@ define([
     var resizeEvent = 'resize.select2.' + container.id;
     var orientationEvent = 'orientationchange.select2.' + container.id;
 
+    $watchers = this.$container.parents().filter(Utils.hasScroll);
+    $watchers.off(scrollEvent);
+
     $(window).off(scrollEvent + ' ' + resizeEvent + ' ' + orientationEvent);
   };
 

src/js/select2/utils.js

@@ -193,5 +193,30 @@ define([], function () {
     return data;
   };
 
+  Utils.hasScroll = function (index, el) {
+    // Adapted from the function created by @ShadowScripter
+    // and adapted by @BillBarry on the Stack Exchange Code Review website.
+    // The original code can be found at
+    // http://codereview.stackexchange.com/q/13338
+    // and was designed to be used with the Sizzle selector engine.
+
+    var $el = $(el);
+    var overflowX = el.style.overflowX;
+    var overflowY = el.style.overflowY;
+
+    //Check both x and y declarations
+    if (overflowX === overflowY &&
+        (overflowY === 'hidden' || overflowY === 'visible')) {
+      return false;
+    }
+
+    if (overflowX === 'scroll' || overflowY === 'scroll') {
+      return true;
+    }
+
+    return ($el.innerHeight() < el.scrollHeight ||
+      $el.innerWidth() < el.scrollWidth);
+  };
+
   return Utils;
 });