Add shift-tab keyboard support for dialogs (modal & Offcanvas components) (#33865)

* consolidate dialog focus trap logic

* add shift-tab support to focustrap

* remove redundant null check of trap element

Co-authored-by: GeoSot <geo.sotis@gmail.com>

* remove area support forom focusableChildren

* fix no expectations warning in focustrap tests

Co-authored-by: GeoSot <geo.sotis@gmail.com>
Co-authored-by: XhmikosR <xhmikosr@gmail.com>

js/src/offcanvas.js

@@ -18,6 +18,7 @@ import BaseComponent from './base-component'
 import SelectorEngine from './dom/selector-engine'
 import Manipulator from './dom/manipulator'
 import Backdrop from './util/backdrop'
+import FocusTrap from './util/focustrap'
 
 /**
  * ------------------------------------------------------------------------
@@ -52,7 +53,6 @@ const EVENT_SHOW = `show${EVENT_KEY}`
 const EVENT_SHOWN = `shown${EVENT_KEY}`
 const EVENT_HIDE = `hide${EVENT_KEY}`
 const EVENT_HIDDEN = `hidden${EVENT_KEY}`
-const EVENT_FOCUSIN = `focusin${EVENT_KEY}`
 const EVENT_CLICK_DATA_API = `click${EVENT_KEY}${DATA_API_KEY}`
 const EVENT_CLICK_DISMISS = `click.dismiss${EVENT_KEY}`
 const EVENT_KEYDOWN_DISMISS = `keydown.dismiss${EVENT_KEY}`
@@ -73,6 +73,7 @@ class Offcanvas extends BaseComponent {
     this._config = this._getConfig(config)
     this._isShown = false
     this._backdrop = this._initializeBackDrop()
+    this._focustrap = this._initializeFocusTrap()
     this._addEventListeners()
   }
 
@@ -110,7 +111,6 @@ class Offcanvas extends BaseComponent {
 
     if (!this._config.scroll) {
       new ScrollBarHelper().hide()
-      this._enforceFocusOnElement(this._element)
     }
 
     this._element.removeAttribute('aria-hidden')
@@ -119,6 +119,10 @@ class Offcanvas extends BaseComponent {
     this._element.classList.add(CLASS_NAME_SHOW)
 
     const completeCallBack = () => {
+      if (!this._config.scroll) {
+        this._focustrap.activate()
+      }
+
       EventHandler.trigger(this._element, EVENT_SHOWN, { relatedTarget })
     }
 
@@ -136,7 +140,7 @@ class Offcanvas extends BaseComponent {
       return
     }
 
-    EventHandler.off(document, EVENT_FOCUSIN)
+    this._focustrap.deactivate()
     this._element.blur()
     this._isShown = false
     this._element.classList.remove(CLASS_NAME_SHOW)
@@ -160,8 +164,8 @@ class Offcanvas extends BaseComponent {
 
   dispose() {
     this._backdrop.dispose()
+    this._focustrap.deactivate()
     super.dispose()
-    EventHandler.off(document, EVENT_FOCUSIN)
   }
 
   // Private
@@ -186,16 +190,10 @@ class Offcanvas extends BaseComponent {
     })
   }
 
-  _enforceFocusOnElement(element) {
-    EventHandler.off(document, EVENT_FOCUSIN) // guard against infinite focus loop
-    EventHandler.on(document, EVENT_FOCUSIN, event => {
-      if (document !== event.target &&
-        element !== event.target &&
-        !element.contains(event.target)) {
-        element.focus()
-      }
+  _initializeFocusTrap() {
+    return new FocusTrap({
+      trapElement: this._element
     })
-    element.focus()
   }
 
   _addEventListeners() {