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Performance Optimization

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Performance optimization in Angular applications is crucial for ensuring a smooth and responsive user experience. This section will cover various techniques and best practices to enhance the performance of your Angular applications.

Key Concepts

  1. Change Detection Strategy
  2. OnPush Change Detection
  3. Lazy Loading Modules
  4. Ahead-of-Time (AOT) Compilation
  5. TrackBy in ngFor
  6. Pure Pipes
  7. Optimizing Template Expressions
  8. Using Web Workers
  9. Efficient Event Handling
  10. Minimizing Bundle Size

Change Detection Strategy

Angular's change detection mechanism is responsible for updating the view whenever the application state changes. By default, Angular uses the Default change detection strategy, which checks every component in the application tree. This can be optimized using the OnPush change detection strategy.

OnPush Change Detection

The OnPush change detection strategy tells Angular to check a component only when its input properties change. This can significantly reduce the number of checks Angular performs.

import { Component, ChangeDetectionStrategy, Input } from '@angular/core';

@Component({
  selector: 'app-optimized-component',
  template: `<p>{{ data }}</p>`,
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class OptimizedComponent {
  @Input() data: string;
}

Lazy Loading Modules

Lazy loading allows you to load feature modules only when they are needed, reducing the initial load time of the application.

Example

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

Ahead-of-Time (AOT) Compilation

AOT compilation pre-compiles your application during the build process, resulting in faster rendering in the browser.

Enabling AOT

ng build --aot

TrackBy in ngFor

Using trackBy in ngFor helps Angular track items in a list more efficiently, reducing the number of DOM manipulations.

Example

<div *ngFor="let item of items; trackBy: trackByFn">
  {{ item.name }}
</div>
trackByFn(index, item) {
  return item.id; // or any unique identifier
}

Pure Pipes

Pure pipes are stateless and only re-evaluate when their input changes, making them more efficient than impure pipes.

Example

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'purePipe',
  pure: true
})
export class PurePipe implements PipeTransform {
  transform(value: any, ...args: any[]): any {
    // transformation logic
  }
}

Optimizing Template Expressions

Avoid complex logic in template expressions to reduce the number of calculations Angular performs during change detection.

Example

<!-- Avoid this -->
<div>{{ complexCalculation() }}</div>

<!-- Prefer this -->
<div>{{ result }}</div>
ngOnInit() {
  this.result = this.complexCalculation();
}

Using Web Workers

Web Workers allow you to run background tasks without blocking the main thread, improving the performance of your application.

Example

if (typeof Worker !== 'undefined') {
  const worker = new Worker(new URL('./app.worker', import.meta.url));
  worker.onmessage = ({ data }) => {
    console.log(`page got message: ${data}`);
  };
  worker.postMessage('hello');
}

Efficient Event Handling

Debounce or throttle events to prevent excessive function calls, especially for events like scroll or resize.

Example

import { fromEvent } from 'rxjs';
import { debounceTime } from 'rxjs/operators';

fromEvent(window, 'resize')
  .pipe(debounceTime(300))
  .subscribe(() => {
    // handle resize
  });

Minimizing Bundle Size

Reducing the size of your application bundle can significantly improve load times.

Techniques

  • Tree Shaking: Remove unused code.
  • Code Splitting: Split your code into smaller chunks.
  • Minification: Minify your JavaScript and CSS files.

Example

ng build --prod

Summary

In this section, we covered various techniques to optimize the performance of Angular applications, including:

  • Using OnPush change detection strategy.
  • Implementing lazy loading for feature modules.
  • Enabling AOT compilation.
  • Utilizing trackBy in ngFor.
  • Creating pure pipes.
  • Optimizing template expressions.
  • Leveraging Web Workers for background tasks.
  • Efficiently handling events.
  • Minimizing the bundle size.

By applying these techniques, you can significantly enhance the performance and responsiveness of your Angular applications.

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