test(docs-infra): improve typeahead example and add unit test (#34190)

This commit improves the typeahead example, by using the emitted input
value. It also adds a unit test to ensure that the example is working
as intended.

PR Close #34190

aio/content/examples/practical-observable-usage/src/typeahead.spec.ts

@@ -0,0 +1,72 @@
+import { of } from 'rxjs';
+import { docRegionTypeahead } from './typeahead';
+
+describe('typeahead', () => {
+  let document;
+  let ajax;
+  let triggertInputChange;
+
+  beforeEach(() => {
+    jasmine.clock().install();
+    const input = {
+      addEventListener: jasmine
+        .createSpy('addEvent')
+        .and.callFake((eventName: string, cb: (e) => void) => {
+          if (eventName === 'input') {
+            triggertInputChange = cb;
+          }
+        }),
+      removeEventListener: jasmine.createSpy('removeEvent'),
+    };
+
+    document = { getElementById: (id: string) => input };
+    ajax = jasmine.createSpy('ajax').and.callFake((url: string) => of('foo bar'));
+  });
+
+  afterEach(() => {
+    jasmine.clock().uninstall();
+  });
+
+  it('should make an ajax call to the corrent endpoint', () => {
+    docRegionTypeahead(document, ajax);
+    triggertInputChange({ target: { value: 'foo' } });
+    jasmine.clock().tick(11);
+    expect(ajax).toHaveBeenCalledWith('/api/endpoint?search=foo');
+  });
+
+  it('should not make an ajax call, when the input length < 3', () => {
+    docRegionTypeahead(document, ajax);
+    triggertInputChange({ target: { value: '' } });
+    jasmine.clock().tick(11);
+    expect(ajax).not.toHaveBeenCalled();
+    triggertInputChange({ target: { value: 'fo' } });
+    jasmine.clock().tick(11);
+    expect(ajax).not.toHaveBeenCalled();
+  });
+
+  it('should not make an ajax call for intermediate values when debouncing', () => {
+    docRegionTypeahead(document, ajax);
+    triggertInputChange({ target: { value: 'foo' } });
+    jasmine.clock().tick(9);
+    triggertInputChange({ target: { value: 'bar' } });
+    jasmine.clock().tick(9);
+    triggertInputChange({ target: { value: 'baz' } });
+    jasmine.clock().tick(9);
+    triggertInputChange({ target: { value: 'qux' } });
+    expect(ajax).not.toHaveBeenCalled();
+    jasmine.clock().tick(10);
+    expect(ajax).toHaveBeenCalledTimes(1);
+    expect(ajax).toHaveBeenCalledWith('/api/endpoint?search=qux');
+  });
+
+  it('should not make an ajax call, when the input value has not changed', () => {
+    docRegionTypeahead(document, ajax);
+    triggertInputChange({ target: { value: 'foo' } });
+    jasmine.clock().tick(11);
+    expect(ajax).toHaveBeenCalled();
+    ajax.calls.reset();
+    triggertInputChange({ target: { value: 'foo' } });
+    jasmine.clock().tick(11);
+    expect(ajax).not.toHaveBeenCalled();
+  });
+});

aio/content/examples/practical-observable-usage/src/typeahead.ts

@@ -1,18 +1,32 @@
-import { fromEvent } from 'rxjs';
-import { ajax } from 'rxjs/ajax';
-import { debounceTime, distinctUntilChanged, filter, map, switchMap } from 'rxjs/operators';
+/*
+  Because of how the code is merged together using the doc regions,
+  we need to indent the imports with the function below.
+*/
+// #docplaster
+// #docregion
+  import { fromEvent } from 'rxjs';
+  import { ajax } from 'rxjs/ajax';
+  import { debounceTime, distinctUntilChanged, filter, map, switchMap } from 'rxjs/operators';
 
+// #enddocregion
+/* tslint:disable:no-shadowed-variable */
+/* tslint:disable:align */
+export function docRegionTypeahead(document, ajax) {
+  // #docregion
+  const searchBox = document.getElementById('search-box');
 
-const searchBox = document.getElementById('search-box');
+  const typeahead = fromEvent(searchBox, 'input').pipe(
+    map((e: KeyboardEvent) => (e.target as HTMLInputElement).value),
+    filter(text => text.length > 2),
+    debounceTime(10),
+    distinctUntilChanged(),
+    switchMap(searchTerm => ajax(`/api/endpoint?search=${searchTerm}`))
+  );
 
-const typeahead = fromEvent(searchBox, 'input').pipe(
-  map((e: KeyboardEvent) => (e.target as HTMLInputElement).value),
-  filter(text => text.length > 2),
-  debounceTime(10),
-  distinctUntilChanged(),
-  switchMap(() => ajax('/api/endpoint'))
-);
+  typeahead.subscribe(data => {
+    // Handle the data from the API
+  });
 
-typeahead.subscribe(data => {
- // Handle the data from the API
-});
+  // #enddocregion
+  return typeahead;
+}