Angular Change Detection Strategy

Introduction

In this blog post, we’ll discuss the OnPush Change Detection Strategy in Angular and how you can implement it in your application to improve performance. If you start to notice poor performance in your Angular application, using the ChangeDetectionStrategy with OnPush can help enhance your app’s performance.

What is OnPush Change Detection Strategy?

The OnPush Change Detection Strategy is an optimization technique that can significantly improve the performance of your Angular application. By default, Angular uses a change detection mechanism that checks for changes in the component’s data bindings whenever an event occurs. This can lead to slow performance, especially when dealing with complex components or large data sets.

With the OnPush strategy, Angular only checks for changes when the component’s input properties change or when an event handler is triggered explicitly within the component. This reduces the number of change detection cycles and improves the overall performance of your application.

Implementing OnPush Change Detection Strategy in Your Angular Application

To enable the OnPush Change Detection Strategy in your Angular component, add the following line to your TypeScript component file:

changeDetection: ChangeDetectionStrategy.OnPush

Here’s a complete example of implementing the OnPush strategy in an Angular component:

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

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.scss'],
  changeDetection: ChangeDetectionStrategy.OnPush,
})
export class TestComponent {
  constructor(private changeDetectorRef: ChangeDetectorRef) {}

  loadSomeData(): void {
    // Load the data by calling endpoints
    //.......

    // To rerender HTML manually after loading data
    this.changeDetectorRef.detectChanges();
  }
}

By adding changeDetection: ChangeDetectionStrategy.OnPush to your component, you deactivate Angular’s default change detection mechanism. This strategy applies to all child directives and cannot be overridden.

When using the OnPush strategy, if you need to force a rerender of the DOM after receiving data from an endpoint, call this.changeDetectorRef.detectChanges();.

This is a basic introduction to the OnPush Change Detection Strategy in Angular. We will discuss this topic in greater detail in future posts.

Keep in mind that the OnPush strategy is not always suitable for every use case, and you should carefully evaluate your application’s requirements before implementing it. However, when used correctly, the OnPush strategy can significantly improve the performance of your Angular application.

Benefits of OnPush Change Detection Strategy

Using the OnPush strategy offers several advantages:

1. Improved Performance: OnPush strategy can significantly improve the performance of your Angular application by reducing unnecessary change detection cycles.
2. Reduced Resource Usage: By limiting change detection to specific components or scenarios, you can minimize the resource usage and save processing power.
3. Control Over Change Detection: OnPush strategy provides better control over when change detection should run, allowing you to optimize your application’s performance.

Understanding Immutable Data and OnPush Strategy

When using the OnPush strategy, it’s essential to understand the concept of immutable data. Immutable data means that once an object is created, it cannot be changed. Instead, any modifications will result in a new object being created. This approach can significantly improve the performance of your application when used with the OnPush strategy.

Here’s an example of using immutable data with the OnPush strategy:

@Component({
  selector: 'app-item',
  templateUrl: './item.component.html',
  styleUrls: ['./item.component.scss'],
  changeDetection: ChangeDetectionStrategy.OnPush,
})
export class ItemComponent implements OnChanges {
  @Input() item: Item;

  ngOnChanges(changes: SimpleChanges): void {
    if (changes.item) {
      // Perform any necessary updates based on the new item data
    }
  }
}

In this example, the ItemComponent uses the OnPush strategy and expects an immutable Item object as input. By following this pattern, you can ensure that Angular only runs change detection when the input object changes.

Conclusion

By incorporating the OnPush change detection strategy in your Angular application, you can improve its performance, reduce resource usage, and gain better control over the change detection process. Remember to use immutable data and understand when and how to trigger change detection manually for the best results.

Further Reading

To deepen your understanding of the OnPush change detection strategy and optimize your Angular applications further, consider exploring the following resources:

1. Angular Change Detection Strategy: OnPush: A comprehensive article that explains how the OnPush change detection strategy works and provides examples of its usage.
2. Angular Performance Tuning with OnPush: This blog post offers practical advice on how to optimize your Angular application’s performance using the OnPush strategy.
3. Optimizing Angular Applications with Immutable.js and OnPush Change Detection: Learn how to use Immutable.js library with OnPush change detection strategy to build high-performance Angular applications.
4. Angular Change Detection Explained: A deep dive into the inner workings of Angular’s change detection mechanism, providing a solid foundation for understanding OnPush and other change detection strategies.
5. Angular.io - Change Detection: The official Angular documentation on change detection, covering various strategies, including OnPush, and how they impact your application’s performance.

By exploring these resources, you will gain valuable insights into the OnPush change detection strategy and learn best practices for improving your Angular application’s performance.

Feedback and Questions:

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1. Email: shady@shadynagy.com
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We’ll do our best to address any questions or concerns you may have. We look forward to hearing from you and helping you make the most of Angular Change Detection Strategy!