Performance optimization is crucial for ensuring that your Angular applications run smoothly and efficiently, providing a better user experience. This section will cover various techniques and best practices to optimize the performance of your Angular applications.
Key Concepts
- Change Detection Strategy
- Lazy Loading Modules
- OnPush Change Detection
- TrackBy with ngFor
- Pure Pipes
- Ahead-of-Time (AOT) Compilation
- Service Workers and Caching
- Optimizing Template Expressions
- Using Web Workers
- 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.
Example
import { ChangeDetectionStrategy, Component } from '@angular/core';
@Component({
selector: 'app-optimized-component',
template: `<p>{{ data }}</p>`,
changeDetection: ChangeDetectionStrategy.OnPush
})
export class OptimizedComponent {
data = 'Optimized Data';
}Explanation
- ChangeDetectionStrategy.OnPush: This strategy tells Angular to check the component only when its input properties change or an event is triggered within the component.
Lazy Loading Modules
Lazy loading is a technique that loads modules only when they are needed, reducing the initial load time of the application.
Example
// app-routing.module.ts
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
const routes: Routes = [
{ path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }Explanation
- loadChildren: This property is used to specify the module to be lazy-loaded. The module is loaded only when the user navigates to the specified route.
OnPush Change Detection
Using the OnPush change detection strategy can significantly improve performance by reducing the number of change detection cycles.
Example
import { ChangeDetectionStrategy, Component, Input } from '@angular/core';
@Component({
selector: 'app-onpush-component',
template: `<p>{{ data }}</p>`,
changeDetection: ChangeDetectionStrategy.OnPush
})
export class OnPushComponent {
@Input() data: string;
}Explanation
- @Input(): The component will only be checked for changes when the
datainput property changes.
TrackBy with ngFor
Using trackBy with ngFor helps Angular track items in a list more efficiently, reducing the number of DOM manipulations.
Example
Explanation
- trackBy: This function helps Angular identify items in the list by a unique identifier, improving performance when the list changes.
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
return transformedValue;
}
}Explanation
- pure: true: This property indicates that the pipe is pure and will only re-evaluate when its input changes.
Ahead-of-Time (AOT) Compilation
AOT compilation pre-compiles the application during the build process, reducing the amount of work the browser needs to do at runtime.
Example
Explanation
- --aot: This flag enables AOT compilation, resulting in faster rendering and smaller bundle sizes.
Service Workers and Caching
Service workers can cache assets and API responses, improving load times and providing offline capabilities.
Example
Explanation
- @angular/pwa: This package adds service worker support to your Angular application, enabling caching and offline capabilities.
Optimizing Template Expressions
Avoid complex logic in template expressions to reduce the number of calculations during change detection.
Example
<!-- Avoid this -->
<p>{{ complexCalculation() }}</p>
<!-- Prefer this -->
<p>{{ calculatedValue }}</p>Explanation
- calculatedValue: Pre-calculate values in the component class to avoid complex calculations in the template.
Using Web Workers
Web workers can offload heavy computations to a background thread, keeping the UI responsive.
Example
if (typeof Worker !== 'undefined') {
const worker = new Worker('./app.worker', { type: 'module' });
worker.onmessage = ({ data }) => {
console.log(`page got message: ${data}`);
};
worker.postMessage('hello');
}Explanation
- Worker: This API allows you to run scripts in background threads, improving performance for heavy computations.
Minimizing Bundle Size
Minimizing the bundle size reduces the amount of code the browser needs to download and parse.
Techniques
- Tree Shaking: Remove unused code.
- Code Splitting: Split the code into smaller chunks.
- Minification: Minify the code to reduce its size.
Example
Explanation
- --prod: This flag enables production optimizations, including tree shaking, code splitting, and minification.
Summary
In this section, we covered various techniques to optimize the performance of Angular applications, including change detection strategies, lazy loading, using trackBy with ngFor, pure pipes, AOT compilation, service workers, optimizing template expressions, using web workers, and minimizing bundle size. By implementing these techniques, you can significantly improve the performance and user experience of your Angular applications.
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