httpResource (Angular 21)

What is httpResource?

httpResource is an Angular 21 primitive from @angular/common/http that provides declarative HTTP data loading. It returns a Resource signal that automatically handles loading states, errors, and provides reactive updates.

Why Use It?

✅ Declarative data loading - URL-based resource definition
✅ Automatic state management - Loading, error, and value states
✅ Signal-based - Returns Resource<T> signal
✅ Manual reload - Trigger refetch with reload()
✅ Type-safe - Full TypeScript support
✅ Simpler than HttpClient - Less boilerplate

httpResource vs HttpClient

Feature	`HttpClient`	`httpResource`
API	Observable-based	Signal-based Resource
Loading state	Manual	Automatic
Error state	Manual try/catch	Automatic
Subscription	Required	Not required
Cleanup	Manual unsubscribe	Automatic
Result type	`Observable<T>`	`Resource<T>`
Reload	Re-call method	Call `.reload()`

Basic Usage

import { Injectable, inject } from '@angular/core';
import { HttpClient, httpResource } from '@angular/common/http';
import { Album } from '../models/album.model';

@Injectable({ providedIn: 'root' })
export class AlbumService {
  http = inject(HttpClient);

  // Define the httpResource
  readonly _albumsResource = httpResource<Album[]>(() => {
    return 'http://localhost:3000/albums';
  }, { defaultValue: [] });

  // Expose as a getter
  get albumsResource() {
    return this._albumsResource;
  }

  // Traditional HttpClient method (for comparison)
  findAll(): Observable<Album[]> {
    return this.http.get<Album[]>('http://localhost:3000/albums');
  }
}

Key points:

Returns a URL string from the loader function
Automatically creates a GET request
defaultValue provides initial value before data loads
Resource is read-only, exposed via getter

import { Component, inject, computed } from '@angular/core';
import { AlbumService } from './services/album.service';

@Component({
  selector: 'app-album-list',
  standalone: true,
  template: `
    <div>
      <!-- Loading state -->
      @if (albumsResource.isLoading()) {
        <p>Loading albums...</p>
      }

      <!-- Error state -->
      @if (albumsResource.error()) {
        <p class="error">Error: {{ albumsResource.error()?.message }}</p>
      }

      <!-- Data -->
      @if (albums(); as albumList) {
        <div class="album-grid">
          @for (album of albumList; track album.id) {
            <div class="album-card">
              <h3>{{ album.name }}</h3>
              <p>{{ album.artist }}</p>
              <p class="price">{{ album.price | currency }}</p>
            </div>
          }
        </div>
      }

      <!-- Reload button -->
      <button (click)="albumsResource.reload()">
        🔄 Reload Albums
      </button>

      <!-- Status -->
      <p>Status: {{ albumsResource.status() }}</p>
    </div>
  `
})
export class AlbumListComponent {
  private albumService = inject(AlbumService);

  // Get the resource from service
  albumsResource = this.albumService.albumsResource;

  // Extract value using computed
  albums = computed(() => this.albumsResource.value());

  // Resource provides:
  // - value()      → Album[] | undefined
  // - isLoading()  → boolean
  // - error()      → Error | undefined
  // - status()     → ResourceStatus
  // - reload()     → void (trigger refetch)
}

Resource provides 4 key signals:

// 1. value() - The loaded data
const albums = this.albumsResource.value();
// Type: Album[] | undefined

// 2. isLoading() - Loading state
const loading = this.albumsResource.isLoading();
// Type: boolean

// 3. error() - Error state
const err = this.albumsResource.error();
// Type: Error | undefined

// 4. status() - Overall status
const status = this.albumsResource.status();
// Type: ResourceStatus
// Values: ResourceStatus.Idle | ResourceStatus.Loading |
//         ResourceStatus.Error | ResourceStatus.Resolved

State transitions:

Initial → Idle (with defaultValue)
   ↓
Loading → isLoading() = true
   ↓
Success → value() = data, isLoading() = false, status() = Resolved
   OR
Error → error() = Error, isLoading() = false, status() = Error

Reload After Mutations

A common pattern is to reload the resource after creating, updating, or deleting items:

Service with CRUD
Reload After Create

@Injectable({ providedIn: 'root' })
export class AlbumService {
  http = inject(HttpClient);

  // Resource for GET
  readonly _albumsResource = httpResource<Album[]>(() => {
    return 'http://localhost:3000/albums';
  }, { defaultValue: [] });

  get albumsResource() {
    return this._albumsResource;
  }

  // Traditional methods for mutations
  save(album: Album): Observable<Album> {
    return this.http.post<Album>('http://localhost:3000/albums', album);
  }

  update(album: Album): Observable<Album> {
    return this.http.put<Album>(`http://localhost:3000/albums/${album.id}`, album);
  }

  delete(id: number): Observable<void> {
    return this.http.delete<void>(`http://localhost:3000/albums/${id}`);
  }
}

import { Component, inject } from '@angular/core';
import { MatDialog, MatDialogRef } from '@angular/material/dialog';
import { AlbumService } from './services/album.service';
import { AddAlbumDialogComponent } from './add-album-dialog.component';

@Component({
  selector: 'app-album-list',
  standalone: true,
  template: `
    <button (click)="openAddDialog()">➕ Add Album</button>

    @for (album of albums(); track album.id) {
      <div class="album-card">
        <h3>{{ album.name }}</h3>
        <p>{{ album.artist }}</p>
        <button (click)="deleteAlbum(album.id)">🗑️ Delete</button>
      </div>
    }
  `
})
export class AlbumListComponent {
  private albumService = inject(AlbumService);
  private dialog = inject(MatDialog);

  albumsResource = this.albumService.albumsResource;
  albums = computed(() => this.albumsResource.value());

  openAddDialog() {
    const dialogRef = this.dialog.open(AddAlbumDialogComponent);

    // Reload resource after dialog closes
    dialogRef.afterClosed().subscribe(() => {
      this.albumsResource.reload();
    });
  }

  deleteAlbum(id: number) {
    this.albumService.delete(id).subscribe({
      next: () => {
        // Reload resource after successful delete
        this.albumsResource.reload();
      },
      error: (err) => console.error('Delete failed:', err)
    });
  }
}

Pattern:

Perform mutation (POST, PUT, DELETE) using HttpClient
On success, call resource.reload() to refetch data
Resource automatically updates all computed values

Advanced Patterns

Default Value

Provide initial data while loading:

readonly albumsResource = httpResource<Album[]>(() => {
  return 'http://localhost:3000/albums';
}, {
  defaultValue: [] // Start with empty array, not undefined
});

Benefits:

Prevents undefined errors in templates
Can show placeholder data
Smoother UX during initial load

Computed Derived Values

Use computed() to derive additional signals:

export class AlbumListComponent {
  albumsResource = this.albumService.albumsResource;

  // Extract value
  albums = computed(() => this.albumsResource.value() ?? []);

  // Derived computations
  totalAlbums = computed(() => this.albums().length);

  highlightedAlbums = computed(() =>
    this.albums().filter(a => a.highlighted)
  );

  totalPrice = computed(() =>
    this.albums().reduce((sum, a) => sum + a.price, 0)
  );

  averagePrice = computed(() => {
    const albums = this.albums();
    return albums.length > 0
      ? this.totalPrice() / albums.length
      : 0;
  });
}

Error Handling in Template

template: `
  @if (albumsResource.error(); as err) {
    <div class="error-banner">
      <h3>⚠️ Failed to load albums</h3>
      <p>{{ err.message }}</p>
      <button (click)="albumsResource.reload()">
        🔄 Retry
      </button>
    </div>
  }
`

Loading Skeleton

template: `
  @if (albumsResource.isLoading()) {
    <div class="skeleton-grid">
      @for (i of [1,2,3,4,5,6]; track i) {
        <div class="skeleton-card">
          <div class="skeleton-line"></div>
          <div class="skeleton-line"></div>
        </div>
      }
    </div>
  }

  @if (albums(); as albumList) {
    <!-- Real content -->
  }
`

Comparison with rxResource

Feature	`httpResource`	`rxResource`
Import from	`@angular/common/http`	`@angular/core/rxjs-interop`
Loader	Returns URL string	Returns Observable
HTTP Method	GET only	Any (via Observable)
Use case	Simple GET requests	Complex Observable chains
Example	`() => '/api/albums'`	`() => http.get('/api/albums')`

When to use httpResource:

✅ Simple GET requests
✅ URL-based loading
✅ No complex RxJS operators needed

When to use rxResource:

✅ POST, PUT, DELETE requests
✅ Complex Observable pipelines
✅ Need for RxJS operators (map, filter, etc.)
✅ Multiple HTTP calls combined

// ❌ HttpClient approach - Manual state management
@Component({
  selector: 'app-album-list',
  template: `
    @if (loading) {
      <p>Loading...</p>
    }
    @if (error) {
      <p class="error">{{ error }}</p>
    }
    @if (!loading && !error) {
      @for (album of albums; track album.id) {
        <div>{{ album.name }}</div>
      }
    }
  `
})
export class AlbumListComponent implements OnInit, OnDestroy {
  albums: Album[] = [];
  loading = false;
  error: string | null = null;
  private destroy$ = new Subject<void>();

  ngOnInit() {
    this.loadAlbums();
  }

  loadAlbums() {
    this.loading = true;
    this.error = null;

    this.albumService.findAll()
      .pipe(takeUntil(this.destroy$))
      .subscribe({
        next: (data) => {
          this.albums = data;
          this.loading = false;
        },
        error: (err) => {
          this.error = err.message;
          this.loading = false;
        }
      });
  }

  ngOnDestroy() {
    this.destroy$.next();
    this.destroy$.complete();
  }
}

Issues:

Manual loading/error state management
Need lifecycle hooks (OnInit, OnDestroy)
Manual subscription management
Manual cleanup with takeUntil
More boilerplate code

// ✅ httpResource approach - Automatic state management
@Component({
  selector: 'app-album-list',
  template: `
    @if (albumsResource.isLoading()) {
      <p>Loading...</p>
    }
    @if (albumsResource.error(); as err) {
      <p class="error">{{ err.message }}</p>
    }
    @for (album of albums(); track album.id) {
      <div>{{ album.name }}</div>
    }
  `
})
export class AlbumListComponent {
  private albumService = inject(AlbumService);

  albumsResource = this.albumService.albumsResource;
  albums = computed(() => this.albumsResource.value() ?? []);

  // That's it! No ngOnInit, no subscriptions, no cleanup
}

Benefits:

✅ Automatic state management
✅ No lifecycle hooks needed
✅ No manual subscriptions
✅ Automatic cleanup
✅ Less code, clearer intent

Real-World Example

Complete example from student project (step-17):

@Injectable({ providedIn: 'root' })
export class AlbumService {
  http = inject(HttpClient);

  readonly _albumsResource = httpResource<Album[]>(() => {
    console.log('Loading albums...');
    return 'http://localhost:3000/albums';
  }, { defaultValue: [] });

  get albumsResource() {
    return this._albumsResource;
  }

  save(album: Album): Observable<Album> {
    return this.http.post<Album>('http://localhost:3000/albums', album);
  }

  delete(id: number): Observable<void> {
    return this.http.delete<void>(`http://localhost:3000/albums/${id}`);
  }
}

@Component({
  selector: 'app-album-list',
  standalone: true,
  imports: [CommonModule, CurrencyPipe],
  template: `
    <div class="container">
      <h1>Album Catalog</h1>

      @if (albumsResource.isLoading()) {
        <div class="loading">
          <p>Loading albums...</p>
        </div>
      }

      @if (albumsResource.error(); as err) {
        <div class="error">
          <p>Failed to load albums: {{ err.message }}</p>
          <button (click)="albumsResource.reload()">Retry</button>
        </div>
      }

      @if (albums(); as albumList) {
        <div class="stats">
          <p>Total Albums: {{ totalAlbums() }}</p>
          <p>Average Price: {{ averagePrice() | currency }}</p>
        </div>

        <div class="album-grid">
          @for (album of albumList; track album.id) {
            <div class="album-card">
              <h3>{{ album.name }}</h3>
              <p class="artist">{{ album.artist }}</p>
              <p class="price">{{ album.price | currency }}</p>
              <div class="tags">
                @for (tag of album.tags; track tag) {
                  <span class="tag">{{ tag }}</span>
                }
              </div>
              <button (click)="deleteAlbum(album.id)">Delete</button>
            </div>
          }
        </div>
      }
    </div>
  `
})
export class AlbumListComponent {
  private albumService = inject(AlbumService);

  albumsResource = this.albumService.albumsResource;
  albums = computed(() => this.albumsResource.value() ?? []);

  totalAlbums = computed(() => this.albums().length);

  averagePrice = computed(() => {
    const albums = this.albums();
    if (albums.length === 0) return 0;
    return albums.reduce((sum, a) => sum + a.price, 0) / albums.length;
  });

  deleteAlbum(id: number) {
    this.albumService.delete(id).subscribe({
      next: () => this.albumsResource.reload(),
      error: (err) => console.error('Delete failed:', err)
    });
  }
}

Best Practices

✅ Use httpResource for simple GET requests
✅ Provide defaultValue to avoid undefined errors
✅ Keep resource private (_albumsResource), expose via getter
✅ Use computed() to derive values from resource
✅ Call reload() after mutations (POST, PUT, DELETE)
✅ Handle errors gracefully in template with retry option
✅ Show loading states for better UX
❌ Don’t mutate resource data directly
❌ Don’t use for POST/PUT/DELETE (use HttpClient instead)
❌ Don’t forget to provide type parameter: httpResource<Album[]>()

Common Patterns

Pattern 1: Resource with Computed Filters

albumsResource = this.albumService.albumsResource;
albums = computed(() => this.albumsResource.value() ?? []);

// Filtered views
rockAlbums = computed(() =>
  this.albums().filter(a => a.tags.includes('Rock'))
);

highlightedAlbums = computed(() =>
  this.albums().filter(a => a.highlighted)
);

Pattern 2: Reload on User Action

refreshAlbums() {
  this.albumsResource.reload();
}

createAlbum(album: Album) {
  this.albumService.save(album).subscribe({
    next: () => this.albumsResource.reload()
  });
}

Pattern 3: Error Recovery

template: `
  @if (albumsResource.error()) {
    <div class="error-banner">
      <p>Something went wrong!</p>
      <button (click)="albumsResource.reload()">Try Again</button>
    </div>
  }
`

rxResource - Observable-based resource API
HttpClient - Traditional HTTP client
State Management - Managing application state
Album Model - Data model reference
Signals - Signal fundamentals

Project Reference

See this pattern in action:

Service: src/app/services/album.service.ts
Component: src/app/components/albums/album-list/album-list.component.ts
Learning Path: Day 3, Module 3.6 - Resource API

Last Updated: December 2024 Angular Version: 21+ Status: Current best practice for declarative HTTP loading

httpResource (Angular 21)

What is httpResource?

Why Use It?

httpResource vs HttpClient

Basic Usage

Reload After Mutations

Advanced Patterns

Default Value

Computed Derived Values

Error Handling in Template

Loading Skeleton

Comparison with rxResource

httpResource vs HttpClient

Real-World Example

Best Practices

Common Patterns

Pattern 1: Resource with Computed Filters

Pattern 2: Reload on User Action

Pattern 3: Error Recovery

Related Documentation

Project Reference