feat(elements): implement `NgElementApplicationContext`

packages/elements/src/ng-element-application-context.ts

@@ -0,0 +1,18 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {ApplicationRef, Injector, NgZone} from '@angular/core';
+
+export class NgElementApplicationContext {
+  applicationRef = this.injector.get<ApplicationRef>(ApplicationRef);
+  ngZone = this.injector.get<NgZone>(NgZone);
+
+  constructor(public injector: Injector) {}
+
+  runInNgZone<R>(cb: () => R): R { return this.ngZone.run(cb); }
+}

packages/elements/test/ng-element-application-context_spec.ts

@@ -0,0 +1,52 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {ApplicationRef, Injector, NgZone} from '@angular/core';
+import {NgElementApplicationContext} from '../src/ng-element-application-context';
+
+export function main() {
+  describe('NgElementApplicationContext', () => {
+    let mockInjector: Injector;
+    let mockZone: NgZone;
+    let ctx: NgElementApplicationContext;
+
+    beforeEach(() => {
+      mockZone = new NgZone({});
+      mockInjector = Injector.create([
+        {provide: ApplicationRef, useValue: 'mockApplicationRef'},
+        {provide: NgZone, useValue: mockZone},
+      ]);
+
+      ctx = new NgElementApplicationContext(mockInjector);
+    });
+
+    it('should expose the `ApplicationRef`',
+       () => { expect(ctx.applicationRef as any).toBe('mockApplicationRef'); });
+
+    it('should expose the `Injector`', () => { expect(ctx.injector).toBe(mockInjector); });
+
+    it('should expose the `NgZone`', () => { expect(ctx.ngZone).toBe(mockZone); });
+
+    describe('runInNgZone()', () => {
+      it('should always run the callback inside the Angular zone', () => {
+        (spyOn(NgZone, 'isInAngularZone').and as any).returnValues(false, true);
+        spyOn(mockZone, 'run').and.callThrough();
+        const callbackSpy = (jasmine.createSpy('callback').and as any).returnValues('foo', 'bar');
+
+        const retValues = [
+          ctx.runInNgZone(callbackSpy),
+          ctx.runInNgZone(callbackSpy),
+        ];
+
+        expect(mockZone.run).toHaveBeenCalledTimes(2);
+        expect(callbackSpy).toHaveBeenCalledTimes(2);
+        expect(retValues).toEqual(['foo', 'bar']);
+      });
+    });
+  });
+}