Angular SSR

Implement server-side rendering, hydration, and prerendering in Angular v20+.

Setup

Add SSR to Existing Project

ng add @angular/ssr

This adds:

• @angular/ssr package
• server.ts - Express server
• src/main.server.ts - Server bootstrap
• src/app/app.config.server.ts - Server providers
• Updates angular.json with SSR configuration

Project Structure

src/
├── app/
│   ├── app.config.ts          # Browser config
│   ├── app.config.server.ts   # Server config
│   └── app.routes.ts
├── main.ts                     # Browser bootstrap
├── main.server.ts              # Server bootstrap
server.ts                       # Express server

Configuration

app.config.server.ts

import { ApplicationConfig, mergeApplicationConfig } from '@angular/core';
import { provideServerRendering } from '@angular/platform-server';
import { provideServerRoutesConfig } from '@angular/ssr';
import { appConfig } from './app.config';
import { serverRoutes } from './app.routes.server';

const serverConfig: ApplicationConfig = {
  providers: [
    provideServerRendering(),
    provideServerRoutesConfig(serverRoutes),
  ],
};

export const config = mergeApplicationConfig(appConfig, serverConfig);

Server Routes Configuration

// app.routes.server.ts
import { RenderMode, ServerRoute } from '@angular/ssr';

export const serverRoutes: ServerRoute[] = [
  {
    path: '',
    renderMode: RenderMode.Prerender, // Static at build time
  },
  {
    path: 'products',
    renderMode: RenderMode.Prerender,
  },
  {
    path: 'products/:id',
    renderMode: RenderMode.Server, // Dynamic SSR
  },
  {
    path: 'dashboard',
    renderMode: RenderMode.Client, // Client-only (SPA)
  },
  {
    path: '**',
    renderMode: RenderMode.Server,
  },
];

Render Modes

Hydration

Default Hydration

Hydration is enabled by default with provideClientHydration():

// app.config.ts
import { provideClientHydration } from '@angular/platform-browser';

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

Incremental Hydration

Defer hydration of specific components:

@Component({
  template: `
    <!-- Hydrate when visible -->
    @defer (hydrate on viewport) {
      <app-comments [postId]="postId" />
    } @placeholder {
      <div class="comments-placeholder">Loading comments...</div>
    }
    
    <!-- Hydrate on interaction -->
    @defer (hydrate on interaction) {
      <app-interactive-chart [data]="chartData" />
    }
    
    <!-- Hydrate on idle -->
    @defer (hydrate on idle) {
      <app-recommendations />
    }
    
    <!-- Never hydrate (static only) -->
    @defer (hydrate never) {
      <app-static-footer />
    }
  `,
})
export class Post {
  postId = input.required<string>();
  chartData = input.required<ChartData>();
}

Hydration Triggers

Event Replay

Capture user events before hydration completes:

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

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

Browser-Only Code

Platform Detection

import { PLATFORM_ID, inject } from '@angular/core';
import { isPlatformBrowser, isPlatformServer } from '@angular/common';

@Component({...})
export class My {
  private platformId = inject(PLATFORM_ID);
  
  ngOnInit() {
    if (isPlatformBrowser(this.platformId)) {
      // Browser-only code
      window.addEventListener('scroll', this.onScroll);
    }
  }
}

afterNextRender / afterRender

Run code only in browser after rendering:

import { afterNextRender, afterRender } from '@angular/core';

@Component({...})
export class Chart {
  constructor() {
    // Runs once after first render (browser only)
    afterNextRender(() => {
      this.initChart();
    });
    
    // Runs after every render (browser only)
    afterRender(() => {
      this.updateChart();
    });
  }
  
  private initChart() {
    // Safe to use DOM APIs here
    const canvas = document.getElementById('chart');
    new Chart(canvas, this.config);
  }
}

Inject Browser APIs Safely

// tokens.ts
import { InjectionToken, PLATFORM_ID, inject } from '@angular/core';
import { isPlatformBrowser } from '@angular/common';

export const WINDOW = new InjectionToken<Window | null>('Window', {
  providedIn: 'root',
  factory: () => {
    const platformId = inject(PLATFORM_ID);
    return isPlatformBrowser(platformId) ? window : null;
  },
});

export const LOCAL_STORAGE = new InjectionToken<Storage | null>('LocalStorage', {
  providedIn: 'root',
  factory: () => {
    const platformId = inject(PLATFORM_ID);
    return isPlatformBrowser(platformId) ? localStorage : null;
  },
});

// Usage
@Injectable({ providedIn: 'root' })
export class Storage {
  private storage = inject(LOCAL_STORAGE);
  
  get(key: string): string | null {
    return this.storage?.getItem(key) ?? null;
  }
  
  set(key: string, value: string): void {
    this.storage?.setItem(key, value);
  }
}

Prerendering

Static Routes

// app.routes.server.ts
export const serverRoutes: ServerRoute[] = [
  { path: '', renderMode: RenderMode.Prerender },
  { path: 'about', renderMode: RenderMode.Prerender },
  { path: 'contact', renderMode: RenderMode.Prerender },
  { path: 'blog', renderMode: RenderMode.Prerender },
];

Dynamic Routes with getPrerenderParams

// app.routes.server.ts
import { RenderMode, ServerRoute, PrerenderFallback } from '@angular/ssr';

export const serverRoutes: ServerRoute[] = [
  {
    path: 'products/:id',
    renderMode: RenderMode.Prerender,
    async getPrerenderParams() {
      // Fetch product IDs to prerender
      const response = await fetch('https://api.example.com/products');
      const products = await response.json();
      return products.map((p: Product) => ({ id: p.id }));
    },
    fallback: PrerenderFallback.Server, // SSR for non-prerendered
  },
  {
    path: 'blog/:slug',
    renderMode: RenderMode.Prerender,
    async getPrerenderParams() {
      const posts = await fetchBlogPosts();
      return posts.map(post => ({ slug: post.slug }));
    },
    fallback: PrerenderFallback.Client, // SPA for non-prerendered
  },
];

Prerender Fallback Options

HTTP Caching

TransferState

Automatically transfer HTTP responses from server to client:

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

export const appConfig: ApplicationConfig = {
  providers: [
    provideClientHydration(
      withHttpTransferCacheOptions({
        includePostRequests: true,
        includeRequestsWithAuthHeaders: false,
        filter: (req) => !req.url.includes('/api/realtime'),
      })
    ),
  ],
};

Manual TransferState

import { TransferState, makeStateKey } from '@angular/core';

const PRODUCTS_KEY = makeStateKey<Product[]>('products');

@Injectable({ providedIn: 'root' })
export class Product {
  private http = inject(HttpClient);
  private transferState = inject(TransferState);
  private platformId = inject(PLATFORM_ID);
  
  getProducts(): Observable<Product[]> {
    // Check if data was transferred from server
    if (this.transferState.hasKey(PRODUCTS_KEY)) {
      const products = this.transferState.get(PRODUCTS_KEY, []);
      this.transferState.remove(PRODUCTS_KEY);
      return of(products);
    }
    
    return this.http.get<Product[]>('/api/products').pipe(
      tap(products => {
        // Store for transfer on server
        if (isPlatformServer(this.platformId)) {
          this.transferState.set(PRODUCTS_KEY, products);
        }
      })
    );
  }
}

Build and Deploy

Build Commands

# Build with SSR
ng build

# Output structure
dist/
├── my-app/
│   ├── browser/      # Client assets
│   └── server/       # Server bundle

Run SSR Server

# Development
npm run serve:ssr:my-app

# Production
node dist/my-app/server/server.mjs

Deploy to Node.js Host

// server.ts (generated)
import { APP_BASE_HREF } from '@angular/common';
import { CommonEngine } from '@angular/ssr/node';
import express from 'express';
import { dirname, join, resolve } from 'node:path';
import { fileURLToPath } from 'node:url';
import bootstrap from './src/main.server';

const serverDistFolder = dirname(fileURLToPath(import.meta.url));
const browserDistFolder = resolve(serverDistFolder, '../browser');
const indexHtml = join(serverDistFolder, 'index.server.html');

const app = express();
const commonEngine = new CommonEngine();

app.get('*', express.static(browserDistFolder, { maxAge: '1y', index: false }));

app.get('*', (req, res, next) => {
  commonEngine
    .render({
      bootstrap,
      documentFilePath: indexHtml,
      url: req.originalUrl,
      publicPath: browserDistFolder,
      providers: [{ provide: APP_BASE_HREF, useValue: req.baseUrl }],
    })
    .then((html) => res.send(html))
    .catch((err) => next(err));
});

app.listen(4000, () => {
  console.log('Server listening on http://localhost:4000');
});

For advanced patterns, see [references/ssr-patterns.md](references/ssr-patterns.md).