Why Your Website Is Slow (And How to Fix It) In Angular

Rajesh Gami
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Performance is not a “nice to have” anymore. It is a core product feature. Users today expect websites to load fast, respond instantly, and work smoothly even on slow networks and low-end devices. If your Angular website feels slow, the problem is rarely Angular itself. In most cases, the slowness comes from how the application is built, configured, and deployed.

Angular is a powerful, enterprise-grade framework. It gives you strong structure, tooling, and scalability. But with that power comes responsibility. A poorly structured Angular application can easily become slow, heavy, and hard to maintain. A well-architected Angular application, on the other hand, can be extremely fast and reliable.

This article explains why Angular websites become slow and, more importantly, how to fix them using production-ready, real-world practices. This is written for senior developers who build and maintain large Angular applications, not toy demos.

We will cover:

Real reasons Angular apps slow down
Common mistakes seen in production
Angular-specific performance bottlenecks
Practical fixes with code examples
Build, runtime, and network optimizations
Monitoring and measuring performance correctly

Understanding Slowness: What “Slow” Actually Means

Before fixing performance, we must define what slow means in real-world terms.

A website can be slow in different ways:

Slow initial load – blank screen for several seconds
Slow interaction – clicking buttons feels delayed
UI freezes – scrolling or typing feels laggy
Heavy network usage – too many API calls
Memory leaks – app slows down over time
Slow navigation – route changes take too long

Angular performance problems usually come from over-rendering, unnecessary work, and excessive JavaScript execution.

The Real Reasons Angular Apps Become Slow

1. Large Bundle Size

Angular applications ship JavaScript to the browser. If the bundle is large:

Download time increases
Parse and execution time increases
Time to interactive becomes slower

Common causes:

Importing entire libraries instead of specific modules
No lazy loading
Heavy third-party dependencies
Unused code not tree-shaken

2. Change Detection Running Too Often

Angular’s default change detection strategy checks every component on every async event:

Mouse movement
API response
Timer
Input change

In large applications, this becomes expensive.

3. Poor Component Design

Common issues:

Too much logic inside templates
Heavy calculations in getters
Large components doing multiple jobs
Deep component trees without isolation

4. Unoptimized API Calls

Examples:

Multiple API calls on every route change
Same API called repeatedly
No caching strategy
Large payloads from backend

5. Inefficient List Rendering

Using *ngFor without:

trackBy
Virtual scrolling

This causes Angular to destroy and recreate DOM nodes unnecessarily.

6. Blocking the Main Thread

JavaScript runs on the main thread. Heavy synchronous work like:

Large loops
JSON parsing
Data transformation
Chart rendering

can freeze the UI.

7. No Proper Build Optimizations

Common mistakes:

Running dev builds in production
Source maps enabled in prod
No compression
No CDN usage

Measuring Performance Before Fixing

Never optimize blindly. Measure first.

Browser Tools

Use:

Chrome DevTools Performance tab
Network tab
Lighthouse

Key metrics:

First Contentful Paint (FCP)
Largest Contentful Paint (LCP)
Time to Interactive (TTI)
Total Blocking Time (TBT)

Angular DevTools

Angular DevTools helps:

Inspect component trees
Detect change detection issues
Identify slow components

Fix 1: Reduce Bundle Size

Enable Lazy Loading Properly

Lazy loading is the biggest performance win in Angular.

Bad:

imports: [
  DashboardModule,
  AdminModule
]

Good:

const routes: Routes = [
  {
    path: 'dashboard',
    loadChildren: () =>
      import('./dashboard/dashboard.module')
        .then(m => m.DashboardModule)
  }
];

Each feature module loads only when needed.

Avoid Importing Entire Libraries

Bad:

import * as _ from 'lodash';

Good:

import debounce from 'lodash/debounce';

Better:

Prefer native JavaScript
Use Angular CDK where possible

Remove Unused Dependencies

Regularly audit:

package.json
Third-party libraries

Many apps carry legacy libraries that are no longer used.

Enable Tree Shaking

Angular CLI does this automatically in production builds. Ensure:

ng build --configuration production

Never deploy dev builds.

Fix 2: Optimize Change Detection

Use OnPush Change Detection

Default change detection is expensive.

@Component({
  selector: 'app-user-card',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class UserCardComponent {
  @Input() user!: User;
}

With OnPush, Angular checks the component only when:

Input reference changes
Event originates from the component
Observable emits (via async pipe)

This reduces unnecessary checks drastically.

Avoid Heavy Logic in Templates

Bad:

<div>{{ calculateTotalPrice() }}</div>

Angular calls this method on every change detection cycle.

Good:

totalPrice$ = this.cart$.pipe(
  map(cart => calculateTotal(cart))
);

<div>{{ totalPrice$ | async }}</div>

Use Async Pipe Instead of Subscriptions

Bad:

ngOnInit() {
  this.userService.getUser().subscribe(user => {
    this.user = user;
  });
}

Good:

user$ = this.userService.getUser();

<div *ngIf="user$ | async as user">
  {{ user.name }}
</div>

Benefits:

Automatic unsubscribe
Cleaner code
Better performance

Fix 3: Improve List Rendering

Use trackBy with ngFor

Bad:

<li *ngFor="let item of items">

Good:

<li *ngFor="let item of items; trackBy: trackById">

trackById(index: number, item: Item) {
  return item.id;
}

This prevents DOM re-creation when data changes.

Use Virtual Scrolling for Large Lists

Angular CDK provides virtual scroll.

<cdk-virtual-scroll-viewport itemSize="50">
  <div *cdkVirtualFor="let item of items">
    {{ item.name }}
  </div>
</cdk-virtual-scroll-viewport>

Only visible items are rendered.

Fix 4: Reduce API and Network Overhead

Cache API Responses

Use RxJS shareReplay.

users$ = this.http.get<User[]>('/api/users')
  .pipe(shareReplay(1));

Avoid repeated calls for same data.

Use Resolver for Route Data

Load data before navigation completes.

resolve(route: ActivatedRouteSnapshot) {
  return this.userService.getUser(route.params['id']);
}

This avoids loading spinners after route activation.

Optimize Backend Payloads

Coordinate with backend teams:

Avoid sending unused fields
Paginate large responses
Compress responses (Gzip/Brotli)

Fix 5: Break Large Components into Smaller Ones

Large components are:

Hard to maintain
Hard to optimize
Expensive to re-render

Best practice:

One component = one responsibility
Use smart (container) and dumb (presentational) components

Fix 6: Avoid Memory Leaks

Unsubscribe Properly

Bad:

this.subscription = observable.subscribe();

Good:

private destroy$ = new Subject<void>();

observable
  .pipe(takeUntil(this.destroy$))
  .subscribe();

ngOnDestroy() {
  this.destroy$.next();
  this.destroy$.complete();
}

Or better, use async pipe.

Fix 7: Web Workers for Heavy Tasks

Offload heavy computation.

const worker = new Worker(
  new URL('./worker.ts', import.meta.url)
);

Use for:

Data processing
File parsing
Complex calculations

Fix 8: Build and Deployment Optimizations

Enable Production Build Settings

Ensure:

AOT enabled
Optimization true
Source maps disabled

Angular CLI does this by default in production config.

Use Compression and CDN

Enable Gzip or Brotli on server
Serve static assets via CDN
Cache assets with long cache headers

Use Preloading Strategy

Load important lazy modules in background.

RouterModule.forRoot(routes, {
  preloadingStrategy: PreloadAllModules
})

Fix 9: Optimize Images and Assets

Use WebP or AVIF
Lazy load images
Avoid large hero images without compression

<img src="image.webp" loading="lazy" />

Fix 10: Continuous Monitoring

Performance is not a one-time task.

Use:

Lighthouse CI
Real User Monitoring (RUM)
Angular DevTools in staging

Track regressions early.

Real-World Angular Performance Checklist

Before every release:

Production build tested
Bundle size reviewed
Lazy loading verified
No console errors
Change detection strategy reviewed
API calls audited
Memory leaks checked

Final Thoughts

Angular is not slow by default. Angular becomes slow when:

Architecture is ignored
Defaults are abused
Performance is treated as an afterthought

By following the practices explained in this article, you can build Angular applications that:

Load fast
Scale well
Stay maintainable for years

Performance is discipline. Angular gives you the tools. It’s up to you to use them correctly.