Angular HTTP & Data Fetching
Fetch data in Angular using signal-based resource(), httpResource(), and the traditional HttpClient.
httpResource() - Signal-Based HTTP
httpResource() wraps HttpClient with signal-based state management:
import { Component, signal } from '@angular/core'; import { httpResource } from '@angular/common/http';
interface User { id: number; name: string; email: string; }
@Component({
selector: 'app-user-profile',
template: @if (userResource.isLoading()) {
<p>Loading...</p>
} @else if (userResource.error()) {
<p>Error: {{ userResource.error()?.message }}</p>
<button (click)="userResource.reload()">Retry</button>
} @else if (userResource.hasValue()) {
<h1>{{ userResource.value().name }}</h1>
<p>{{ userResource.value().email }}</p>
},
})
export class UserProfileComponent {
userId = signal('123');
// Reactive HTTP resource - refetches when userId changes
userResource = httpResource/api/users/${this.userId()});
}
httpResource Options
// Simple GET request
userResource = httpResource/api/users/${this.userId()});
// With full request options
userResource = httpResource/api/users/${this.userId()},
method: 'GET',
headers: { 'Authorization': Bearer ${this.token()} },
params: { include: 'profile' },
}));
// With default value
usersResource = httpResource
// Skip request when params undefined
userResource = httpResource/api/users/${id} : undefined;
});
Resource State // Status signals userResource.value() // Current value or undefined userResource.hasValue() // Boolean - has resolved value userResource.error() // Error or undefined userResource.isLoading() // Boolean - currently loading userResource.status() // 'idle' | 'loading' | 'reloading' | 'resolved' | 'error' | 'local'
// Actions userResource.reload() // Manually trigger reload userResource.set(value) // Set local value userResource.update(fn) // Update local value
resource() - Generic Async Data
For non-HTTP async operations or custom fetch logic:
import { resource, signal } from '@angular/core';
@Component({...}) export class SearchComponent { query = signal('');
searchResource = resource({ // Reactive params - triggers reload when changed params: () => ({ q: this.query() }),
// Async loader function
loader: async ({ params, abortSignal }) => {
if (!params.q) return [];
const response = await fetch(`/api/search?q=${params.q}`, {
signal: abortSignal,
});
return response.json() as Promise<SearchResult[]>;
},
}); }
Resource with Default Value
todosResource = resource({
defaultValue: [] as Todo[],
params: () => ({ filter: this.filter() }),
loader: async ({ params }) => {
const res = await fetch(/api/todos?filter=${params.filter});
return res.json();
},
});
// value() returns Todo[] (never undefined)
Conditional Loading
const userId = signal
userResource = resource({
params: () => {
const id = userId();
// Return undefined to skip loading
return id ? { id } : undefined;
},
loader: async ({ params }) => {
return fetch(/api/users/${params.id}).then(r => r.json());
},
});
// Status is 'idle' when params returns undefined
HttpClient - Traditional Approach
For complex scenarios or when you need Observable operators:
import { Component, inject } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { toSignal } from '@angular/core/rxjs-interop';
@Component({...}) export class UsersComponent { private http = inject(HttpClient);
// Convert Observable to Signal
users = toSignal(
this.http.get
// Or use Observable directly
users$ = this.http.get
HTTP Methods private http = inject(HttpClient);
// GET
getUser(id: string) {
return this.http.get/api/users/${id});
}
// POST
createUser(user: CreateUserDto) {
return this.http.post
// PUT
updateUser(id: string, user: UpdateUserDto) {
return this.http.put/api/users/${id}, user);
}
// PATCH
patchUser(id: string, changes: Partial/api/users/${id}, changes);
}
// DELETE
deleteUser(id: string) {
return this.http.delete/api/users/${id});
}
Request Options
this.http.get
Interceptors Functional Interceptor (Recommended) // auth.interceptor.ts import { HttpInterceptorFn } from '@angular/common/http'; import { inject } from '@angular/core';
export const authInterceptor: HttpInterceptorFn = (req, next) => { const authService = inject(AuthService); const token = authService.token();
if (token) {
req = req.clone({
setHeaders: { Authorization: Bearer ${token} },
});
}
return next(req); };
// error.interceptor.ts export const errorInterceptor: HttpInterceptorFn = (req, next) => { return next(req).pipe( catchError((error: HttpErrorResponse) => { if (error.status === 401) { inject(Router).navigate(['/login']); } return throwError(() => error); }) ); };
// logging.interceptor.ts
export const loggingInterceptor: HttpInterceptorFn = (req, next) => {
const started = Date.now();
return next(req).pipe(
tap({
next: () => console.log(${req.method} ${req.url} - ${Date.now() - started}ms),
error: (err) => console.error(${req.method} ${req.url} failed, err),
})
);
};
Register Interceptors // app.config.ts import { provideHttpClient, withInterceptors } from '@angular/common/http';
export const appConfig: ApplicationConfig = { providers: [ provideHttpClient( withInterceptors([ authInterceptor, errorInterceptor, loggingInterceptor, ]) ), ], };
Error Handling
With httpResource
@Component({
template: @if (userResource.error(); as error) {
<div class="error">
<p>{{ getErrorMessage(error) }}</p>
<button (click)="userResource.reload()">Retry</button>
</div>
},
})
export class UserComponent {
userResource = httpResource/api/users/${this.userId()});
getErrorMessage(error: unknown): string {
if (error instanceof HttpErrorResponse) {
return error.error?.message || Error ${error.status}: ${error.statusText};
}
return 'An unexpected error occurred';
}
}
With HttpClient import { catchError, retry } from 'rxjs';
getUser(id: string) {
return this.http.get/api/users/${id}).pipe(
retry(2), // Retry up to 2 times
catchError((error: HttpErrorResponse) => {
console.error('Error fetching user:', error);
return throwError(() => new Error('Failed to load user'));
})
);
}
Loading States Pattern
@Component({
template: @switch (dataResource.status()) {
@case ('idle') {
<p>Enter a search term</p>
}
@case ('loading') {
<app-spinner />
}
@case ('reloading') {
<app-data [data]="dataResource.value()" />
<app-spinner size="small" />
}
@case ('resolved') {
<app-data [data]="dataResource.value()" />
}
@case ('error') {
<app-error
[error]="dataResource.error()"
(retry)="dataResource.reload()"
/>
}
},
})
export class DataComponent {
query = signal('');
dataResource = httpResource/api/search?q=${this.query()} : undefined
);
}
For advanced patterns, see references/http-patterns.md.