Add static backdrop to offcanvas (#35832)

* Add static backdrop option,  to offcanvas
* Trigger prevented event on esc with keyboard=false
* Change offcanvas doc , moving backdrop examples to examples section

js/src/offcanvas.js

@@ -39,6 +39,7 @@ const OPEN_SELECTOR = '.offcanvas.show'
 const EVENT_SHOW = `show${EVENT_KEY}`
 const EVENT_SHOWN = `shown${EVENT_KEY}`
 const EVENT_HIDE = `hide${EVENT_KEY}`
+const EVENT_HIDE_PREVENTED = `hidePrevented${EVENT_KEY}`
 const EVENT_HIDDEN = `hidden${EVENT_KEY}`
 const EVENT_CLICK_DATA_API = `click${EVENT_KEY}${DATA_API_KEY}`
 const EVENT_KEYDOWN_DISMISS = `keydown.dismiss${EVENT_KEY}`
@@ -52,7 +53,7 @@ const Default = {
 }
 
 const DefaultType = {
-  backdrop: 'boolean',
+  backdrop: '(boolean|string)',
   keyboard: 'boolean',
   scroll: 'boolean'
 }
@@ -164,12 +165,24 @@ class Offcanvas extends BaseComponent {
 
   // Private
   _initializeBackDrop() {
+    const clickCallback = () => {
+      if (this._config.backdrop === 'static') {
+        EventHandler.trigger(this._element, EVENT_HIDE_PREVENTED)
+        return
+      }
+
+      this.hide()
+    }
+
+    // 'static' option will be translated to true, and booleans will keep their value
+    const isVisible = Boolean(this._config.backdrop)
+
     return new Backdrop({
       className: CLASS_NAME_BACKDROP,
-      isVisible: this._config.backdrop,
+      isVisible,
       isAnimated: true,
       rootElement: this._element.parentNode,
-      clickCallback: () => this.hide()
+      clickCallback: isVisible ? clickCallback : null
     })
   }
 
@@ -181,9 +194,16 @@ class Offcanvas extends BaseComponent {
 
   _addEventListeners() {
     EventHandler.on(this._element, EVENT_KEYDOWN_DISMISS, event => {
-      if (this._config.keyboard && event.key === ESCAPE_KEY) {
-        this.hide()
+      if (event.key !== ESCAPE_KEY) {
+        return
       }
+
+      if (!this._config.keyboard) {
+        EventHandler.trigger(this._element, EVENT_HIDE_PREVENTED)
+        return
+      }
+
+      this.hide()
     })
   }