angular-performance

---

name: angular-performance description: Angular performance. Trigger: optimizing Angular apps, images, lazy loading. allowed-tools: [Read, Edit, Write, Glob, Grep, Bash]

NgOptimizedImage (REQUIRED for images)

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

@Component({
  imports: [NgOptimizedImage],
  template: `
    <!-- LCP image: add priority -->
    <img ngSrc="hero.jpg" width="800" height="400" priority>
    
    <!-- Regular: lazy loaded by default -->
    <img ngSrc="thumb.jpg" width="200" height="200">
    
    <!-- Fill mode (parent needs position: relative) -->
    <img ngSrc="bg.jpg" fill>
    
    <!-- With placeholder -->
    <img ngSrc="photo.jpg" width="400" height="300" placeholder>
  `
})

Rules

• ALWAYS set width and height (or fill)
• Add priority to LCP (Largest Contentful Paint) image
• Use ngSrc not src
• Parent of fill image must have position: relative/fixed/absolute

---

@defer - Lazy Components

@defer (on viewport) {
  <heavy-component />
} @placeholder {
  <p>Placeholder shown immediately</p>
} @loading (minimum 200ms) {
  <spinner />
} @error {
  <p>Failed to load</p>
}

Triggers

Trigger	When to Use
on viewport	Below the fold content
on interaction	Load on click/focus/hover
on idle	Load when browser is idle
on timer(500ms)	Load after delay
when condition	Load when expression is true

<!-- Multiple triggers -->
@defer (on viewport; on interaction) {
  <comments />
}

<!-- Conditional -->
@defer (when showComments()) {
  <comments />
}

---

Lazy Routes

// Single component
{
  path: 'admin',
  loadComponent: () => import('./features/admin/admin').then(c => c.AdminComponent)
}

// Feature with child routes
{
  path: 'users',
  loadChildren: () => import('./features/users/routes').then(m => m.USERS_ROUTES)
}

---

SSR & Hydration

bootstrapApplication(AppComponent, {
  providers: [
    provideClientHydration()
  ]
});

Scenario	Use
SEO critical (blog, e-commerce)	SSR
Dashboard/Admin	CSR
Static marketing site	SSG/Prerender

---

Slow Computations

Solution	When
Optimize algorithm	First choice always
Pure pipes	Cache single result
Memoization	Cache multiple results
computed()	Derived signal state

NEVER trigger reflows/repaints in lifecycle hooks (ngOnInit, ngAfterViewInit).

---

Resources

• https://angular.dev/guide/image-optimization
• https://angular.dev/guide/defer
• https://angular.dev/best-practices/runtime-performance
• https://angular.dev/guide/ssr