@angular/ssr (Server-Side Rendering)

Version: Angular 21 (2025) Tags: SSR, Hydration, Prerendering, SEO, Angular Universal

References: SSR Guide • Hydration • @angular/ssr

API Changes

This section documents recent version-specific API changes.

• NEW: Incremental Hydration — Hydrate components incrementally instead of all at once source

• NEW: Hybrid Rendering — Per-route rendering mode configuration source

• NEW: provideClientHydration — Modern hydration setup with event replay

• NEW: Deferrable views (@defer) — Load components lazily with SSR support

• NEW: ngSkipHydration — Opt-out of hydration for specific components

• DEPRECATED: Angular Universal — Migrate to @angular/ssr

Best Practices

• Enable SSR with CLI

ng add @angular/ssr

# Or create new project with SSR
ng new my-app --ssr

• Enable client hydration

import { provideClientHydration } from '@angular/platform-browser';

export const appConfig: ApplicationConfig = {
  providers: [
    provideClientHydration()
  ]
};

• Use incremental hydration for better performance

import { provideClientHydration, withIncrementalHydration } from '@angular/platform-browser';

export const appConfig: ApplicationConfig = {
  providers: [
    provideClientHydration(withIncrementalHydration())
  ]
};

• Use @defer for lazy loading

@Component({
  template: `
    @defer (on viewport) {
      <heavy-component />
    } @placeholder {
      <div>Loading...</div>
    }
  `
})
export class MainComponent {}

• Handle browser-specific code with isPlatformBrowser

import { PLATFORM_ID, Inject } from '@angular/core';

constructor(@Inject(PLATFORM_ID) private platformId: Object) {
  if (isPlatformBrowser(this.platformId)) {
    // Browser-only code
  }
}

• Use TransferState to prevent duplicate HTTP requests

import { TransferState, makeStateKey } from '@angular/platform-browser';

@Injectable()
export class DataService {
  constructor(private http: HttpClient, private transferState: TransferState) {}

  getData() {
    const DATA_KEY = makeStateKey('DATA');
    
    if (this.transferState.hasKey(DATA_KEY)) {
      return of(this.transferState.get(DATA_KEY, []));
    }
    
    return this.http.get('/api/data').pipe(
      tap(data => this.transferState.set(DATA_KEY, data))
    );
  }
}

• Skip hydration for DOM-manipulating components

@Component({
  selector: 'app-third-party',
  host: {
    'ngSkipHydration': 'true'
  }
})
export class ThirdPartyComponent {}

• Configure hybrid rendering per route

import { RenderMode, ServerRoute } from '@angular/ssr';

export const serverRoutes: ServerRoute[] = [
  {
    path: 'dashboard',
    renderMode: RenderMode.Client
  },
  {
    path: 'blog/:slug',
    renderMode: RenderMode.Server
  },
  {
    path: 'about',
    renderMode: RenderMode.Prerender
  }
];

• Use platform-server for server-side logic

import { isPlatformServer } from '@angular/common';

constructor(@Inject(PLATFORM_ID) platformId: Object) {
  if (isPlatformServer(platformId)) {
    // Server-side only
  }
}