feat: Add Optimistic Updates Example for Angular

examples/angular/optimistic-updates/.devcontainer/devcontainer.json

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+{
+  "name": "Node.js",
+  "image": "mcr.microsoft.com/devcontainers/javascript-node:22"
+}

examples/angular/optimistic-updates/.eslintrc.cjs

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+// @ts-check
+
+/** @type {import('eslint').Linter.Config} */
+const config = {}
+
+module.exports = config

examples/angular/optimistic-updates/README.md

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+# TanStack Query Angular optimistic-updates example
+
+To run this example:
+
+- `npm install` or `yarn` or `pnpm i` or `bun i`
+- `npm run start` or `yarn start` or `pnpm start` or `bun start`

examples/angular/optimistic-updates/angular.json

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+{
+  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
+  "version": 1,
+  "cli": {
+    "packageManager": "pnpm",
+    "analytics": false,
+    "cache": {
+      "enabled": false
+    }
+  },
+  "newProjectRoot": "projects",
+  "projects": {
+    "optimistic-updates": {
+      "projectType": "application",
+      "schematics": {
+        "@schematics/angular:component": {
+          "inlineTemplate": true,
+          "inlineStyle": true,
+          "skipTests": true
+        },
+        "@schematics/angular:class": {
+          "skipTests": true
+        },
+        "@schematics/angular:directive": {
+          "skipTests": true
+        },
+        "@schematics/angular:guard": {
+          "skipTests": true
+        },
+        "@schematics/angular:interceptor": {
+          "skipTests": true
+        },
+        "@schematics/angular:pipe": {
+          "skipTests": true
+        },
+        "@schematics/angular:resolver": {
+          "skipTests": true
+        },
+        "@schematics/angular:service": {
+          "skipTests": true
+        }
+      },
+      "root": "",
+      "sourceRoot": "src",
+      "prefix": "app",
+      "architect": {
+        "build": {
+          "builder": "@angular/build:application",
+          "options": {
+            "outputPath": "dist/optimistic-updates",
+            "index": "src/index.html",
+            "browser": "src/main.ts",
+            "polyfills": ["zone.js"],
+            "tsConfig": "tsconfig.app.json",
+            "assets": ["src/favicon.ico", "src/assets"],
+            "styles": [],
+            "scripts": []
+          },
+          "configurations": {
+            "production": {
+              "budgets": [
+                {
+                  "type": "initial",
+                  "maximumWarning": "500kb",
+                  "maximumError": "1mb"
+                },
+                {
+                  "type": "anyComponentStyle",
+                  "maximumWarning": "2kb",
+                  "maximumError": "4kb"
+                }
+              ],
+              "outputHashing": "all"
+            },
+            "development": {
+              "optimization": false,
+              "extractLicenses": false,
+              "sourceMap": true
+            }
+          },
+          "defaultConfiguration": "production"
+        },
+        "serve": {
+          "builder": "@angular/build:dev-server",
+          "configurations": {
+            "production": {
+              "buildTarget": "optimistic-updates:build:production"
+            },
+            "development": {
+              "buildTarget": "optimistic-updates:build:development"
+            }
+          },
+          "defaultConfiguration": "development"
+        },
+        "extract-i18n": {
+          "builder": "@angular/build:extract-i18n",
+          "options": {
+            "buildTarget": "optimistic-updates:build"
+          }
+        }
+      }
+    }
+  }
+}

examples/angular/optimistic-updates/package.json

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+{
+  "name": "@tanstack/query-example-angular-optimistic-updates",
+  "type": "module",
+  "scripts": {
+    "ng": "ng",
+    "start": "ng serve",
+    "build": "ng build",
+    "watch": "ng build --watch --configuration development"
+  },
+  "private": true,
+  "dependencies": {
+    "@angular/common": "^19.1.0-next.0",
+    "@angular/compiler": "^19.1.0-next.0",
+    "@angular/core": "^19.1.0-next.0",
+    "@angular/forms": "19.1.0-next.0",
+    "@angular/platform-browser": "^19.1.0-next.0",
+    "@angular/platform-browser-dynamic": "^19.1.0-next.0",
+    "@tanstack/angular-query-experimental": "^5.62.7",
+    "rxjs": "^7.8.1",
+    "tslib": "^2.6.3",
+    "zone.js": "^0.15.0"
+  },
+  "devDependencies": {
+    "@angular/build": "^19.0.2",
+    "@angular/cli": "^19.0.2",
+    "@angular/compiler-cli": "^19.1.0-next.0",
+    "typescript": "5.7.2"
+  }
+}

examples/angular/optimistic-updates/src/app/app.component.ts

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+import { ChangeDetectionStrategy, Component } from '@angular/core'
+import { OptimisticUpdatesComponent } from './components/optimistic-updates.component'
+
+@Component({
+  changeDetection: ChangeDetectionStrategy.OnPush,
+  selector: 'app-root',
+  standalone: true,
+  template: `<optimistic-updates />`,
+  imports: [OptimisticUpdatesComponent],
+})
+export class AppComponent {}

examples/angular/optimistic-updates/src/app/app.config.ts

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+import {
+  provideHttpClient,
+  withFetch,
+  withInterceptors,
+} from '@angular/common/http'
+import {
+  QueryClient,
+  provideTanStackQuery,
+  withDevtools,
+} from '@tanstack/angular-query-experimental'
+import { mockInterceptor } from './interceptor/mock-api.interceptor'
+import type { ApplicationConfig } from '@angular/core'
+
+export const appConfig: ApplicationConfig = {
+  providers: [
+    provideHttpClient(withFetch(), withInterceptors([mockInterceptor])),
+    provideTanStackQuery(
+      new QueryClient({
+        defaultOptions: {
+          queries: {
+            gcTime: 1000 * 60 * 60 * 24, // 24 hours
+          },
+        },
+      }),
+      withDevtools(),
+    ),
+  ],
+}

examples/angular/optimistic-updates/src/app/components/optimistic-updates.component.ts

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+import { Component, inject } from '@angular/core'
+import {
+  injectMutation,
+  injectQuery,
+} from '@tanstack/angular-query-experimental'
+import { FormsModule, ReactiveFormsModule } from '@angular/forms'
+import { DatePipe } from '@angular/common'
+import { TasksService } from '../services/tasks.service'
+
+@Component({
+  selector: 'optimistic-updates',
+  imports: [FormsModule, DatePipe],
+  template: `
+    <p>
+      In this example, new items can be created using a mutation. The new item
+      will be optimistically added to the list in hopes that the server accepts
+      the item. If it does, the list is refetched with the true items from the
+      list. Every now and then, the mutation may fail though. When that happens,
+      the previous list of items is restored and the list is again refetched
+      from the server.
+    </p>
+
+    <hr />
+    @if (tasks.isLoading()) {
+      <p>Loading...</p>
+    }
+
+    <div class="container">
+      <label>
+        <input type="checkbox" [(ngModel)]="failMutation" />
+        Fail Mutation
+      </label>
+
+      <div class="input-container">
+        <input type="text" [(ngModel)]="newItem" placeholder="Enter text" />
+        <button (click)="addItem()">Create</button>
+        <ul>
+          @for (task of tasks.data(); track task) {
+            <li>{{ task }}</li>
+          }
+        </ul>
+
+        <div>
+          Updated At: {{ tasks.dataUpdatedAt() | date: 'MMMM d, h:mm:ss a ' }}
+        </div>
+      </div>
+      @if (!tasks.isLoading() && tasks.isFetching()) {
+        <p>Fetching in background</p>
+      }
+    </div>
+  `,
+  styles: ``,
+})
+export class OptimisticUpdatesComponent {
+  #tasksService = inject(TasksService)
+
+  tasks = (() => injectQuery(() => this.#tasksService.allTasks()))()
+  clearMutation = injectMutation(() => this.#tasksService.addTask())
+  addMutation = injectMutation(() => this.#tasksService.addTask())
+
+  newItem = ''
+  failMutation = false
+
+  addItem() {
+    if (!this.newItem) return
+
+    this.addMutation.mutate({
+      task: this.newItem,
+      failMutation: this.failMutation,
+    })
+    this.newItem = ''
+  }
+}

examples/angular/optimistic-updates/src/app/interceptor/mock-api.interceptor.ts

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+/**
+ * MockApiInterceptor is used to simulate API responses for `/api/tasks` endpoints.
+ * It handles the following operations:
+ * - GET: Fetches all tasks from sessionStorage.
+ * - POST: Adds a new task to sessionStorage.
+ * Simulated responses include a delay to mimic network latency.
+ */
+import { HttpResponse } from '@angular/common/http'
+import { delay, of } from 'rxjs'
+import type {
+  HttpEvent,
+  HttpHandlerFn,
+  HttpInterceptorFn,
+  HttpRequest,
+} from '@angular/common/http'
+import type { Observable } from 'rxjs'
+
+export const mockInterceptor: HttpInterceptorFn = (
+  req: HttpRequest<unknown>,
+  next: HttpHandlerFn,
+): Observable<HttpEvent<any>> => {
+  const respondWith = (status: number, body: any) =>
+    of(new HttpResponse({ status, body })).pipe(delay(500))
+  if (req.url === '/api/tasks') {
+    switch (req.method) {
+      case 'GET':
+        return respondWith(
+          200,
+          JSON.parse(
+            sessionStorage.getItem('optimistic-updates-tasks') || '[]',
+          ),
+        )
+      case 'POST':
+        const tasks = JSON.parse(
+          sessionStorage.getItem('optimistic-updates-tasks') || '[]',
+        )
+        tasks.push(req.body)
+        sessionStorage.setItem(
+          'optimistic-updates-tasks',
+          JSON.stringify(tasks),
+        )
+        return respondWith(201, {
+          status: 'success',
+          task: req.body,
+        })
+    }
+  }
+  if (req.url === '/api/tasks-wrong-url') {
+    return respondWith(500, {
+      status: 'error',
+    })
+  }
+
+  return next(req)
+}