Common Practices That Kill Performance in Angular Applications

Angular is a powerful framework that simplifies building dynamic web applications. However, as the application grows, performance issues can creep in, leading to slower load times, sluggish user experiences, and poor scalability. Many of these issues arise from common coding practices or design choices. In this article, we’ll explore these performance pitfalls step by step, providing clear examples and practical solutions so even beginners can improve their Angular applications.

Why Performance Matters in Angular Applications?

Performance in web applications directly impacts user satisfaction, retention, and even revenue. A fast and responsive Angular app ensures smooth user interactions, better search engine rankings, and overall success. By understanding and avoiding bad practices, you can ensure your application remains performant.

1. Unoptimized Change Detection

Why Is It a Problem?

Angular uses a Zone.js-powered change detection mechanism to update the DOM whenever application state changes. However, unnecessary rechecks or poorly implemented components can cause this process to become resource-intensive.

Symptoms

• Frequent or redundant component re-renders.
• Noticeable lags during UI updates.

Example of the Problem

@Component({
  selector: 'app-example',
  template: `<div>{{ computeValue() }}</div>`,
})
export class ExampleComponent {
  computeValue() {
    console.log('Value recomputed!');
    return Math.random();
  }
}

In this example, computeValue() will be called every time Angular’s change detection runs, even when it’s unnecessary.

Solution

Use pure pipes or memoization techniques to prevent expensive recalculations.

Optimized Example:

@Component({
  selector: 'app-example',
  template: `<div>{{ computedValue }}</div>`,
})
export class ExampleComponent implements OnInit {
  computedValue!: number;

  ngOnInit() {
    this.computedValue = this.computeValue();
  }

  computeValue() {
    console.log('Value computed once!');
    return Math.random();
  }
}

Alternatively, use Angular's OnPush Change Detection strategy:

@Component({
  selector: 'app-example',
  template: `<div>{{ computeValue() }}</div>`,
  changeDetection: ChangeDetectionStrategy.OnPush,
})
export class ExampleComponent {
  computeValue() {
    return 'Static Value';
  }
}

2. Using Too Many Observables Without Unsubscribing

Why Is It a Problem?

Unmanaged subscriptions can lead to memory leaks, causing slowdowns and even application crashes.

Symptoms

• Performance degradation over time.
• Increased memory usage in long-running applications.

Example of the Problem

@Component({
  selector: 'app-example',
  template: `<div>{{ data }}</div>`,
})
export class ExampleComponent implements OnInit {
  data!: string;

  ngOnInit() {
    interval(1000).subscribe(() => {
      this.data = 'Updated Data';
    });
  }
}

Here, the subscription never gets cleared, leading to potential memory leaks.

Solution

Always unsubscribe from observables using the takeUntil operator or Angular's async pipe.

Fixed Example:

@Component({
  selector: 'app-example',
  template: `<div>{{ data }}</div>`,
})
export class ExampleComponent implements OnDestroy {
  private destroy$ = new Subject<void>();
  data!: string;

  ngOnInit() {
    interval(1000)
      .pipe(takeUntil(this.destroy$))
      .subscribe(() => {
        this.data = 'Updated Data';
      });
  }

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

Alternatively, use the async pipe to manage subscriptions automatically:

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

3. Overusing Two-Way Binding

Why Is It a Problem?

Two-way binding ([(ngModel)]) keeps your component’s data and the DOM in sync, but overuse can cause excessive change detection and negatively impact performance.

Symptoms

• Laggy forms or UI elements.
• Increased CPU usage during typing or interaction.

Example of the Problem

<input [(ngModel)]="userInput" />

If userInput is used in multiple places, Angular will keep checking for changes.

Solution

Prefer one-way data binding and handle events explicitly.

Optimized Example:

<input [value]="userInput" (input)="onInputChange($event)" />

@Component({
  selector: 'app-example',
  template: `...`,
})
export class ExampleComponent {
  userInput = '';

  onInputChange(event: Event) {
    this.userInput = (event.target as HTMLInputElement).value;
  }
}

4. Large Bundle Sizes

Why Is It a Problem?

Large bundles increase load times, especially on slower networks.

Symptoms

• Delayed initial load times.
• Users leaving before the app fully loads.

Solution

• Enable lazy loading for feature modules.
• Use tree-shaking to remove unused code.
• Optimize dependencies with tools like Webpack or Angular CLI.

Example of Lazy Loading:

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

5. Inefficient DOM Manipulation

Why Is It a Problem?

Directly manipulating the DOM bypasses Angular’s change detection and can lead to performance bottlenecks.

Symptoms

• UI updates behave unexpectedly.
• Performance issues with dynamic elements.

Example of the Problem

document.getElementById('my-element')?.innerHTML = 'New Content';

Solution

Use Angular’s Renderer2 to manipulate the DOM safely and efficiently.

Fixed Example:

constructor(private renderer: Renderer2) {}

ngOnInit() {
  const element = this.renderer.selectRootElement('#my-element');
  this.renderer.setProperty(element, 'innerHTML', 'New Content');
}

6. Not Using AOT Compilation

Why Is It a Problem?

Angular's Just-in-Time (JIT) compilation is slower and increases bundle size.

Solution

Always use Ahead-of-Time (AOT) compilation in production.

Enable AOT:

ng build --prod

FAQs

How Can I Detect Performance Issues in My Angular Application?

Use tools like Angular DevTools, Lighthouse, and Chrome Developer Tools to identify bottlenecks.

What Are the Best Practices for Angular Performance Optimization?

• Use OnPush change detection.
• Implement lazy loading.
• Optimize observable subscriptions.
• Avoid unnecessary DOM manipulations.

By addressing these common practices that kill performance, you can transform your Angular application from slow and clunky to fast and efficient. Follow these steps carefully, and you’ll be on your way to mastering Angular performance optimization!