Angular 19: Top 4 Features to Improve App Performance

Slow applications can frustrate users, increase infrastructure costs, and put unnecessary pressure on development teams. As applications grow, performance bottlenecks can quickly turn into significant roadblocks, negatively impacting user experience and long-term maintainability.

Angular 19 introduces smarter rendering strategies and enhanced efficiency, helping teams minimize unnecessary processing, optimize resource usage, and maintain smooth application performance – even as complexity increases. 

In this article, you will discover the key features of Angular 19 that enhance your application’s performance. Learn which specific problems they resolve and how to implement these features in practice.

Incremental Hydration (experimental) – Smarter hydration for better performance

Challenge:

Modern web applications demand both high performance and interactivity, especially for server-rendered content. Hydrating an entire application on the client side can be resource-intensive, leading to slower load times and delayed interactivity. Developers need a way to selectively hydrate parts of the application as needed to optimize resource usage and improve the user experience.

 

Solution:

Angular introduces Incremental Hydration as an experimental feature, building on the foundations of defer blocks, deferrable views (introduced in v17), and event replay (v18). This feature hydrates server-rendered sections selectively, depending on predefined triggers. This gives developers control over component activation, enhancing both speed and user experience.

To enable Incremental Hydration, update the application configuration:

export const appConfig: ApplicationConfig = {
  providers: [
    provideClientHydration(
      withIncrementalHydration()
    )
    // other providers...
  ]
};Code language: JavaScript (javascript)

Incremental Hydration works in tandem with defer blocks. To use it, developers can add new hydration triggers to specific components:

@defer (hydrate on hover) {
  <app-hydrated-cmp />
}Code language: HTML, XML (xml)

Supported hydration triggers include:

• Idle: Hydrate during idle time.
• Interaction: Trigger hydration upon user interaction.
• Immediate: Hydrate immediately.
• Timer (ms): Hydrate after a specified delay.
• Hover: Trigger hydration on hover.
• Viewport: Hydrate when the component enters the viewport.
• Never: Keep the component dehydrated indefinitely.
• When {{ condition }}: Conditional hydration based on a specified condition.

These triggers give developers fine-grained control over hydration timing and behavior, optimizing resources based on app needs and user actions.

Benefits:

Incremental Hydration improves load times and interactivity by activating components only when needed, reducing the initial payload and resource consumption. This allows large applications to run more efficiently by hydrating only the necessary components at startup.

In the same way, the flexibility provided by different triggers allows developers to tailor hydration strategies to specific use cases, making applications more efficient and responsive.

Server Route Configuration (experimental) – Easier hybrid rendering and better route control

Challenge:

Hybrid rendering in Angular applications requires a high degree of flexibility to optimize performance and user experience. Without a clear way to define route rendering—server-side, pre-rendered, or client-side—developers rely on complex setups and manual work. The absence of a clear API can lead to inefficiencies and higher maintenance efforts.

 

Solution:

Angular’s experimental Server Route Configuration API lets developers set rendering modes for routes flexibly and declaratively. Using this API, developers can optimize the performance of their applications by choosing the most appropriate rendering strategy for each route, such as server-side rendering (SSR), static site generation (SSG), or client-side rendering (CSR).

Example configuration:

 

import { RenderMode, ServerRoute } from '@angular/ssr';
export const serverRouteConfig: ServerRoute[] = [
  { path: '/login', renderMode: RenderMode.Server },
  { path: '/fruits', renderMode: RenderMode.Prerender },
  { path: '/**', renderMode: RenderMode.Client }
];Code language: JavaScript (javascript)

In this configuration:

• /login: Uses SSR to ensure that the latest data is rendered on every request.
• /fruits: Uses SSG to generate content at build time for faster loading.
• /*: Defaults to CSR for all other routes, optimizing for interactivity.

In addition, the API supports dynamic path parameters in pre-render mode by defining functions to resolve path parameters:

export const serverRouteConfig2: ServerRoute[] = [
  {
    path: '/fruit/:id',
    renderMode: RenderMode.Prerender,
    async getPrerenderParams() {
      const fruitService = inject(FruitService);
      const fruitIds = await fruitService.getAllFruitIds();
      return fruitIds.map(id => ({ id }));
    },
  },
];Code language: JavaScript (javascript)

This example shows how the /fruit/:id route can dynamically generate static pages for all available fruit IDs, guaranteeing optimized performance for frequently accessed resources.

Benefits:

The Server Route Configuration API makes it easier to manage hybrid rendering in Angular applications. It reduces complexity and maintenance by allowing developers to declaratively define rendering modes for specific routes. The ability to dynamically resolve parameters for pre-rendered paths further increases flexibility, making it easier to build high-performance and scalable applications.

Minor signal improvements – Easier Effect Handling and Signal Updates

Challenge:

Reactive programming in Angular previously faced limitations in handling effects and signal updates. The effect() function restricted signal writes, adding additional complexity in certain scenarios. At the same time its execution timing often caused issues with premature or delayed updates. Similarly, the toSignal function lacked flexibility in value comparison, forcing unnecessary updates due to a lack of custom equality logic.

Solution:

Angular 19 tackles these challenges with major updates to effect() and improvements to toSignal.

Removing the allowSignalWrites flag in effect() simplifies usage, letting developers set signals directly without extra restrictions. In addition, effect() execution is now integrated into Angular’s change detection cycle, ensuring logical alignment with the component hierarchy. This eliminates timing issues and makes effect execution more reliable.

effect(
  () => {
      console.log(this.users());
  },
  //This flag is removed in the new version
  { allowSignalWrites: true }
);Code language: JavaScript (javascript)

Angular now supports custom equality functions in toSignal. Developers can set custom equality logic to trigger updates only when meaningful changes are detected, improving performance.

// Create a Subject to emit array values
const arraySubject$ = new Subject<number[]>();
// Define a custom equality function to compare arrays based on their content
const arraysAreEqual = (a: number[], b: number[]): boolean => {
   return a.length === b.length && a.every((value, index) => value === b[index]);
};
// Convert the Subject to a signal with a custom equality function
const arraySignal = toSignal(arraySubject$, {
   initialValue: [1, 2, 3],
   equals: arraysAreEqual, // Custom equality function for arrays
});Code language: JavaScript (javascript)

Benefits:

These updates improve reactive programming in Angular. The revamped effect() function simplifies workflows by removing unnecessary restrictions and ensuring correct execution timing. 

In turn, The custom equality function in toSignal gives more control over updates, reducing unnecessary re-renders and boosting performance. Together, these changes simplify the code, make it easier to maintain, and improve the overall developer experience in Angular apps. 

afterRenderEffect Function (experimental) – Smarter Post-Render Side Effects

Challenge:

Managing side effects that depend on the DOM state in Angular can be challenging, especially when those effects need to take place only after the DOM has been updated. While Angular provides afterRender and afterNextRender to schedule post-render callbacks, these APIs do not track signal dependencies, making them less suitable for scenarios where side effects need to be re-executed based on changes in reactive data. Developers must often resort to manual tracking, which produces complex and less maintainable code.

Solution:

Angular’s afterRenderEffect is an experimental function designed to handle side effects that should only occur after the component has finished rendering and specific dependencies have changed. Unlike afterRender and afterNextRender, which always schedule post-render callbacks without dependency tracking, afterRenderEffect ties callback execution to specific reactive dependencies. This makes it ideal for ongoing post-render tasks tied to dynamic application state.

counter = signal(0);
constructor() {
  afterRenderEffect(() => {
    console.log('after render effect', this.counter());
  })
  afterRender(() => {
    console.log('after render', this.counter())
  })
}Code language: JavaScript (javascript)

In this example, afterRender schedules its callback to run after every render cycle regardless of any state changes. In contrast, afterRenderEffect runs its callback only when the counter signal changes. This ensures that the effect is selectively executed, based on relevant updates, cutting down on unnecessary operations and improving application efficiency.

Benefits:

The afterRenderEffect function offers a powerful tool for managing post-render side effects tied to reactive dependencies. By tracking dependencies and executing only on relevant changes, it simplifies code, reduces boilerplate, and avoids unnecessary executions. 

This makes applications more efficient and easier to maintain, especially in scenarios with frequent state updates and DOM interactions. As an experimental feature, afterRenderEffect lays the groundwork for more sophisticated reactive workflows in the evolving Angular’s ecosystem.

Final Thoughts:

Angular 19 introduces powerful features designed to enhance application performance by optimizing rendering, improving reactivity, and minimizing unnecessary processing. Key updates such as Incremental Hydration, Server Route Configuration, signal improvements, and afterRenderEffect each tackle specific performance challenges, resulting in more efficient and scalable applications. 

If you’re interested in exploring further ways to enhance Angular performance, download our ebook, where we discuss additional features and best practices of the latest Angular versions.