fix(modal): focus stays trapped with Shift+Tab

Closes #2807
Fixes #2718

e2e-app/e2e/src/modal/modal-focus.e2e-spec.ts

@@ -100,17 +100,15 @@ describe('Modal', () => {
     await expectFocused(page.getModalDismissButton(), 'Modal dismiss button should be focused');
   });
 
-  // TODO: this is broken, must be fixed
-  // it('should keep focus trap inside the modal when clicking on content and navigating away (Shift + Tab)', async() =>
-  // {
-  //   const modal = await page.openModal('template');
-  //
-  //   // click on the header
-  //   await page.getModalHeader().click();
-  //   await expectFocused(modal, 'Modal window should be focused');
-  //
-  //   // re-focus
-  //   await sendKey(Key.SHIFT, Key.TAB);
-  //   await expectFocused(page.getModalCloseButton(), 'Modal close button should be focused');
-  // });
+  it('should keep focus trap inside the modal when clicking on content and navigating away (Shift + Tab)', async() => {
+    const modal = await page.openModal('template');
+
+    // click on the header
+    await page.getModalHeader().click();
+    await expectFocused(modal, 'Modal window should be focused');
+
+    // re-focus
+    await sendKey(Key.SHIFT, Key.TAB);
+    await expectFocused(page.getModalCloseButton(), 'Modal close button should be focused');
+  });
 });

src/util/focus-trap.ts

@@ -38,7 +38,7 @@ export const ngbFocusTrap = (element: HTMLElement, stopFocusTrap$: Observable<an
       .subscribe(([tabEvent, focusedElement]) => {
         const[first, last] = getFocusableBoundaryElements(element);
 
-        if (focusedElement === first && tabEvent.shiftKey) {
+        if ((focusedElement === first || focusedElement === element) && tabEvent.shiftKey) {
           last.focus();
           tabEvent.preventDefault();
         }