fixes a potential TypeError: this.element.contains is not a function error in ElementObserver

Author: songjiz

src/core/binding.ts

@@ -96,13 +96,17 @@ export class Binding {
 
     if (this.element === eventTarget) {
       return true
-    } else if (eventTarget instanceof Element && this.element.contains(eventTarget)) {
+    } else if (eventTarget instanceof Element && this.containsElement(eventTarget)) {
       return this.scope.containsElement(eventTarget)
     } else {
       return this.scope.containsElement(this.action.element)
     }
   }
 
+  private containsElement(element: Element): boolean {
+    return HTMLElement.prototype.contains.call(this.element, element)
+  }
+
   private get controller(): Controller {
     return this.context.controller
   }

src/mutation-observers/element_observer.ts

@@ -146,7 +146,7 @@ export class ElementObserver {
     if (element.isConnected != this.element.isConnected) {
       return false
     } else {
-      return this.element.contains(element)
+      return this.containsElement(element)
     }
   }
 
@@ -171,4 +171,8 @@ export class ElementObserver {
       }
     }
   }
+
+  private containsElement(element: Element): boolean {
+    return HTMLElement.prototype.contains.call(this.element, element)
+  }
 }