Change detection is core to Angular performance and responsiveness. Understanding how it works and how to optimize it makes a noticeable difference in how Angular apps behave under load.
Core Concepts in Angular Change Detection
Angular’s change detection keeps component data in sync with the DOM. It sets up a change detector for each component, creating a tree structure that imitates the component hierarchy.
When an event gets triggered, Angular runs change detection across the entire tree, from top to bottom. It checks each component for changes, and if it finds one, it updates only that part of the view accordingly.
Optimization with OnPush Strategy
In large-scale apps, the default detection strategy can slow things down. That’s where OnPush comes in. By using the OnPush change detection strategy, Angular only runs checks when:
- An @Input() property changes
- An event is emitted from the component or its children
- You manually trigger change detection using ChangeDetectorRef
This reduces unnecessary updates and improves performance.
Example
ts
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import { Component, Input, ChangeDetectionStrategy } from '@angular/core';
@Component({ selector: 'app-user-profile', template: ` <h2>{{ user.name }}</h2> <p>{{ user.email }}</p> `, changeDetection: ChangeDetectionStrategy.OnPush
})
export class UserProfileComponent { @Input() user: { name: string, email: string };
}In this setup, UserProfileComponent only updates its view when the user object reference changes, not when just one of its properties changes. This prevents Angular from running change detection unnecessarily.
Conclusion
Getting familiar with Angular’s change detection and learning when to use OnPush can improve performance without adding complexity. If you’re working on a demanding project, it’s worth considering whether now is the time to hire Angular developers who can help you structure components more efficiently.
