Angular
Improving Angular Performance with OnPush Change Detection
Introduction
Angular is a powerful framework for building dynamic web applications, but as your application grows, performance bottlenecks can arise. One of the most effective ways to optimize performance in Angular is by using the OnPush change detection strategy. In this, we’ll explore how Angular's change detection works, the benefits of OnPush, and how to implement it effectively.
Understanding Change Detection in Angular
Angular employs a change-detection mechanism to update the UI once the application's state changes. As a default, Angular uses the Default change detection strategy, where it checks the whole component tree each time a change is detected, which might result in un-noteworthy performance overhead in large-scale applications.
How Change Detection Works
- As soon as the event (like user input) happens, Angular checks all components for changes.
- Even if the data of a component hasn't been changed, it still recomputes it.
- This leads to computations that are not needed, hence reducing performance
What is OnPush Change Detection?
The OnPush strategy is an optimal approach for change detection. Upon setting, Angular checks a component only when:
The component has been provided with new values for any @Input() with a different reference
Event is occurring within the component
This change detection was manually called (ChangeDetectorRef.markForCheck()).
Advantages of Using OnPush
- Improved Performance: It limits the times Angular re-evaluates the components.
- Optimized Rendering: Updates only the relevant components, reducing DOM manipulations.
- Better Scalability: Suitable for massive applications with lots of parts.
Implementing OnPush in Angular
Step 1: Enable OnPush Strategy
To use OnPush, update your component decorator as follows:
import { ChangeDetectionStrategy, Component, Input } from '@angular/core';@Component({ selector: 'app-example', templateUrl: './example.component.html', changeDetection: ChangeDetectionStrategy.OnPush})export class ExampleComponent { @Input() data: any;}
Step 2: Ensure Immutable Data
Since OnPush only detects changes when a new reference is assigned, always use immutable objects:
this.data = { ...this.data, newValue: 'Updated' }; // Creates a new reference
Step 3: Using ChangeDetectorRef
If you need to trigger change detection manually:
import { ChangeDetectorRef } from '@angular/core';constructor(private cdr: ChangeDetectorRef) {}updateData() { this.data = { ...this.data, newValue: 'Updated' }; this.cdr.markForCheck(); // Manually trigger change detection}When Not to Use OnPush
- When dealing with local variables that don't change reference.
- When using ngModel or two-way binding.
- When relying on event-driven or deeply nested state changes.
Conclusion
Using OnPush in Angular can significantly enhance performance by reducing unnecessary checks and updates in the component tree. By ensuring immutable data structures and using ChangeDetectorRef where necessary, you can build highly efficient and scalable applications
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