snapshot of https://github.com/TanStack/query.git (main, 2026-09-16; blobs > 131072B omitted)

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',
+  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,
+} from '@tanstack/angular-query-experimental'
+import { withDevtools } from '@tanstack/angular-query-experimental/devtools'
+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 { ChangeDetectionStrategy, Component, inject } from '@angular/core'
+import {
+  injectMutation,
+  injectQuery,
+} from '@tanstack/angular-query-experimental'
+import { FormsModule } from '@angular/forms'
+import { DatePipe } from '@angular/common'
+import { TasksService } from '../services/tasks.service'
+
+@Component({
+  changeDetection: ChangeDetectionStrategy.OnPush,
+  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>
+  `,
+})
+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(1000))
+  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)
+}

examples/angular/optimistic-updates/src/app/services/tasks.service.ts

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+import { HttpClient } from '@angular/common/http'
+import { Injectable, inject } from '@angular/core'
+import {
+  QueryClient,
+  mutationOptions,
+  queryOptions,
+} from '@tanstack/angular-query-experimental'
+
+import { lastValueFrom } from 'rxjs'
+
+@Injectable({
+  providedIn: 'root',
+})
+export class TasksService {
+  #queryClient = inject(QueryClient) // Manages query state and caching
+  #http = inject(HttpClient) // Handles HTTP requests
+
+  /**
+   * Fetches all tasks from the API.
+   * Returns an observable containing an array of task strings.
+   */
+  allTasks = () =>
+    queryOptions({
+      queryKey: ['tasks'],
+      queryFn: () => {
+        return lastValueFrom(this.#http.get<Array<string>>('/api/tasks'))
+      },
+    })
+
+  /**
+   * Creates a mutation for adding a task.
+   * On success, invalidates and refetches the "tasks" query cache to update the task list.
+   */
+  addTask() {
+    return mutationOptions({
+      mutationFn: ({
+        task,
+        failMutation = false,
+      }: {
+        task: string
+        failMutation: boolean
+      }) =>
+        lastValueFrom(
+          this.#http.post(
+            `/api/tasks${failMutation ? '-wrong-url' : ''}`,
+            task,
+          ),
+        ),
+      mutationKey: ['tasks'],
+      onSuccess: () => {
+        this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
+      },
+      onMutate: async ({ task }) => {
+        // Cancel any outgoing refetches
+        // (so they don't overwrite our optimistic update)
+        await this.#queryClient.cancelQueries({ queryKey: ['tasks'] })
+
+        // Snapshot the previous value
+        const previousTodos = this.#queryClient.getQueryData<Array<string>>([
+          'tasks',
+        ])
+
+        // Optimistically update to the new value
+        if (previousTodos) {
+          this.#queryClient.setQueryData<Array<string>>(
+            ['tasks'],
+            [...previousTodos, task],
+          )
+        }
+
+        return previousTodos
+      },
+      onError: (err, variables, context) => {
+        if (context) {
+          this.#queryClient.setQueryData<Array<string>>(['tasks'], context)
+        }
+      },
+      // Always refetch after error or success:
+      onSettled: () => {
+        this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
+      },
+    })
+  }
+}

examples/angular/optimistic-updates/src/index.html

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+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title>TanStack Query Angular Optimistic Updates Example</title>
+    <base href="/" />
+    <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <link rel="icon" type="image/x-icon" href="favicon.ico" />
+  </head>
+  <body>
+    <app-root></app-root>
+  </body>
+</html>

examples/angular/optimistic-updates/src/main.ts

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+import { bootstrapApplication } from '@angular/platform-browser'
+import { appConfig } from './app/app.config'
+import { AppComponent } from './app/app.component'
+
+bootstrapApplication(AppComponent, appConfig).catch((err) => console.error(err))