fix(aria-describer): exception when attempting to describe a non-element node (#9392)

* Fixes an error that was being thrown when trying to describe a non-element node. This could happen if the consumer is attempting to describe an `ng-container` which corresponds to a comment node.
* Switches a few cases, that had hard-coded the `Node.ELEMENT_NODE` constant for to Universal compatibility, to take the constant from the `Document`.

Relates to #8724.

src/cdk/a11y/aria-describer.spec.ts

@@ -107,6 +107,11 @@ describe('AriaDescriber', () => {
     expectMessages(['My Message']);
     expectMessage(component.element1, 'My Message');
   });
+
+  it('should not throw when attempting to describe a non-element node', () => {
+    const node: any = document.createComment('Not an element node');
+    expect(() => ariaDescriber.describe(node, 'This looks like an element')).not.toThrow();
+  });
 });
 
 function getMessagesContainer() {

src/cdk/a11y/aria-describer.ts

@@ -60,7 +60,7 @@ export class AriaDescriber {
    * message element.
    */
   describe(hostElement: Element, message: string) {
-    if (!message.trim()) {
+    if (hostElement.nodeType !== this._document.ELEMENT_NODE || !message.trim()) {
       return;
     }
 
@@ -75,7 +75,7 @@ export class AriaDescriber {
 
   /** Removes the host element's aria-describedby reference to the message element. */
   removeDescription(hostElement: Element, message: string) {
-    if (!message.trim()) {
+    if (hostElement.nodeType !== this._document.ELEMENT_NODE || !message.trim()) {
       return;
     }
 

src/cdk/a11y/focus-trap.ts

@@ -21,12 +21,6 @@ import {take} from 'rxjs/operators/take';
 import {InteractivityChecker} from './interactivity-checker';
 import {DOCUMENT} from '@angular/common';
 
-/**
- * Node type of element nodes. Used instead of Node.ELEMENT_NODE
- * which is unsupported in Universal.
- * @docs-private
- */
-const ELEMENT_NODE_TYPE = 1;
 
 /**
  * Class that allows for trapping focus within a DOM element.
@@ -229,7 +223,7 @@ export class FocusTrap {
     let children = root.children || root.childNodes;
 
     for (let i = 0; i < children.length; i++) {
-      let tabbableChild = children[i].nodeType === ELEMENT_NODE_TYPE ?
+      let tabbableChild = children[i].nodeType === this._document.ELEMENT_NODE ?
         this._getFirstTabbableElement(children[i] as HTMLElement) :
         null;
 
@@ -251,7 +245,7 @@ export class FocusTrap {
     let children = root.children || root.childNodes;
 
     for (let i = children.length - 1; i >= 0; i--) {
-      let tabbableChild = children[i].nodeType === ELEMENT_NODE_TYPE ?
+      let tabbableChild = children[i].nodeType === this._document.ELEMENT_NODE ?
         this._getLastTabbableElement(children[i] as HTMLElement) :
         null;
 

src/lib/icon/icon-registry.ts

@@ -78,6 +78,8 @@ class SvgIconConfig {
  */
 @Injectable()
 export class MatIconRegistry {
+  private _document: Document;
+
   /**
    * URLs and cached SVG elements for individual icons. Keys are of the format "[namespace]:[icon]".
    */
@@ -108,8 +110,9 @@ export class MatIconRegistry {
   constructor(
     @Optional() private _httpClient: HttpClient,
     private _sanitizer: DomSanitizer,
-    @Optional() @Inject(DOCUMENT) private _document?: any) {
+    @Optional() @Inject(DOCUMENT) document?: any) {
       // TODO(crisbeto): make _document required next major release.
+      this._document = document;
     }
 
   /**
@@ -438,8 +441,7 @@ export class MatIconRegistry {
     let svg = this._svgElementFromString('<svg></svg>');
 
     for (let i = 0; i < element.childNodes.length; i++) {
-      // Note: 1 corresponds to `Node.ELEMENT_NODE` which we can't use in Universal.
-      if (element.childNodes[i].nodeType === 1) {
+      if (element.childNodes[i].nodeType === this._document.ELEMENT_NODE) {
         svg.appendChild(element.childNodes[i].cloneNode(true));
       }
     }