fix(focus-trap): exception when element contains SVG on IE (#3432)

Fixes an exception being thrown by the focus trap, if it contains an SVG element on IE. The problem was that on IE, SVG elements don't have the `children` property, which means that we have to fall back to `childNodes`.

Fixes #3410.

src/lib/core/a11y/focus-trap.spec.ts

@@ -9,7 +9,13 @@ describe('FocusTrap', () => {
 
   beforeEach(async(() => {
     TestBed.configureTestingModule({
-      declarations: [FocusTrapDirective, FocusTrapWithBindings, SimpleFocusTrap, FocusTrapTargets],
+      declarations: [
+        FocusTrapDirective,
+        FocusTrapWithBindings,
+        SimpleFocusTrap,
+        FocusTrapTargets,
+        FocusTrapWithSvg
+      ],
       providers: [InteractivityChecker, Platform, FocusTrapFactory]
     });
 
@@ -112,6 +118,20 @@ describe('FocusTrap', () => {
       expect(document.activeElement.id).toBe('last');
     });
   });
+
+  describe('special cases', () => {
+    it('should not throw when it has a SVG child', () => {
+      let fixture = TestBed.createComponent(FocusTrapWithSvg);
+
+      fixture.detectChanges();
+
+      let focusTrapInstance = fixture.componentInstance.focusTrapDirective.focusTrap;
+
+      expect(() => focusTrapInstance.focusFirstTabbableElement()).not.toThrow();
+      expect(() => focusTrapInstance.focusLastTabbableElement()).not.toThrow();
+    });
+  });
+
 });
 
 
@@ -156,3 +176,17 @@ class FocusTrapWithBindings {
 class FocusTrapTargets {
   @ViewChild(FocusTrapDirective) focusTrapDirective: FocusTrapDirective;
 }
+
+
+@Component({
+  template: `
+    <div cdkTrapFocus>
+      <svg xmlns="http://www.w3.org/2000/svg">
+        <circle cx="100" cy="100" r="100"/>
+      </svg>
+    </div>
+    `
+})
+class FocusTrapWithSvg {
+  @ViewChild(FocusTrapDirective) focusTrapDirective: FocusTrapDirective;
+}

src/lib/core/a11y/focus-trap.ts

@@ -128,10 +128,15 @@ export class FocusTrap {
       return root;
     }
 
-    // Iterate in DOM order.
-    let childCount = root.children.length;
-    for (let i = 0; i < childCount; i++) {
-      let tabbableChild = this._getFirstTabbableElement(root.children[i] as HTMLElement);
+    // Iterate in DOM order. Note that IE doesn't have `children` for SVG so we fall
+    // back to `childNodes` which includes text nodes, comments etc.
+    let children = root.children || root.childNodes;
+
+    for (let i = 0; i < children.length; i++) {
+      let tabbableChild = children[i].nodeType === Node.ELEMENT_NODE ?
+        this._getFirstTabbableElement(children[i] as HTMLElement) :
+        null;
+
       if (tabbableChild) {
         return tabbableChild;
       }
@@ -147,8 +152,13 @@ export class FocusTrap {
     }
 
     // Iterate in reverse DOM order.
-    for (let i = root.children.length - 1; i >= 0; i--) {
-      let tabbableChild = this._getLastTabbableElement(root.children[i] as HTMLElement);
+    let children = root.children || root.childNodes;
+
+    for (let i = children.length - 1; i >= 0; i--) {
+      let tabbableChild = children[i].nodeType === Node.ELEMENT_NODE ?
+        this._getLastTabbableElement(children[i] as HTMLElement) :
+        null;
+
       if (tabbableChild) {
         return tabbableChild;
       }