feat(aio): add component for lazy-loading custom element (#23944)

PR Close #23944

aio/src/app/custom-elements/custom-elements.module.ts

@@ -6,8 +6,11 @@ import {
   ELEMENT_MODULE_PATHS_AS_ROUTES,
   ELEMENT_MODULE_PATHS_TOKEN
 } from './element-registry';
+import { LazyCustomElementComponent } from './lazy-custom-element.component';
 
 @NgModule({
+  declarations: [ LazyCustomElementComponent ],
+  exports: [ LazyCustomElementComponent ],
   providers: [
     ElementsLoader,
     { provide: NgModuleFactoryLoader, useClass: SystemJsNgModuleLoader },

aio/src/app/custom-elements/lazy-custom-element.component.spec.ts

@@ -0,0 +1,67 @@
+import { ComponentFixture, TestBed } from '@angular/core/testing';
+import { Logger } from 'app/shared/logger.service';
+import { MockLogger } from 'testing/logger.service';
+import { LazyCustomElementComponent } from './lazy-custom-element.component';
+import { ElementsLoader } from './elements-loader';
+
+describe('LazyCustomElementComponent', () => {
+  let mockElementsLoader: jasmine.SpyObj<ElementsLoader>;
+  let mockLogger: MockLogger;
+  let fixture: ComponentFixture<LazyCustomElementComponent>;
+
+  beforeEach(() => {
+    mockElementsLoader = jasmine.createSpyObj<ElementsLoader>('ElementsLoader', [
+      'loadContainingCustomElements',
+      'loadCustomElement',
+    ]);
+
+    const injector = TestBed.configureTestingModule({
+      declarations: [ LazyCustomElementComponent ],
+      providers: [
+        { provide: ElementsLoader, useValue: mockElementsLoader },
+        { provide: Logger, useClass: MockLogger },
+      ],
+    });
+
+    mockLogger = injector.get(Logger);
+    fixture = TestBed.createComponent(LazyCustomElementComponent);
+  });
+
+  it('should set the HTML content based on the selector', () => {
+    const elem = fixture.nativeElement;
+
+    expect(elem.innerHTML).toBe('');
+
+    fixture.componentInstance.selector = 'foo-bar';
+    fixture.detectChanges();
+
+    expect(elem.innerHTML).toBe('<foo-bar></foo-bar>');
+  });
+
+  it('should load the specified custom element', () => {
+    expect(mockElementsLoader.loadCustomElement).not.toHaveBeenCalled();
+
+    fixture.componentInstance.selector = 'foo-bar';
+    fixture.detectChanges();
+
+    expect(mockElementsLoader.loadCustomElement).toHaveBeenCalledWith('foo-bar');
+  });
+
+  it('should log an error (and abort) if the selector is empty', () => {
+    fixture.detectChanges();
+
+    expect(mockElementsLoader.loadCustomElement).not.toHaveBeenCalled();
+    expect(mockLogger.output.error).toEqual([[jasmine.any(Error)]]);
+    expect(mockLogger.output.error[0][0].message).toBe('Invalid selector for \'aio-lazy-ce\': ');
+  });
+
+  it('should log an error (and abort) if the selector is invalid', () => {
+    fixture.componentInstance.selector = 'foo-bar><script></script><foo-bar';
+    fixture.detectChanges();
+
+    expect(mockElementsLoader.loadCustomElement).not.toHaveBeenCalled();
+    expect(mockLogger.output.error).toEqual([[jasmine.any(Error)]]);
+    expect(mockLogger.output.error[0][0].message).toBe(
+        'Invalid selector for \'aio-lazy-ce\': foo-bar><script></script><foo-bar');
+  });
+});

aio/src/app/custom-elements/lazy-custom-element.component.ts

@@ -0,0 +1,27 @@
+import { Component, ElementRef, Input, OnInit } from '@angular/core';
+import { Logger } from 'app/shared/logger.service';
+import { ElementsLoader } from './elements-loader';
+
+@Component({
+  selector: 'aio-lazy-ce',
+  template: '',
+})
+export class LazyCustomElementComponent implements OnInit {
+  @Input() selector = '';
+
+  constructor(
+    private elementRef: ElementRef,
+    private elementsLoader: ElementsLoader,
+    private logger: Logger,
+  ) {}
+
+  ngOnInit() {
+    if (!this.selector || /[^\w-]/.test(this.selector)) {
+      this.logger.error(new Error(`Invalid selector for 'aio-lazy-ce': ${this.selector}`));
+      return;
+    }
+
+    this.elementRef.nativeElement.innerHTML = `<${this.selector}></${this.selector}>`;
+    this.elementsLoader.loadCustomElement(this.selector);
+  }
+}