Mastering Angular's Change Detection Strategies for Enhanced Performance
Tags: webdev, angular, javascript, typescript
Published: 2023-04-02 22:56:52

## Introduction

Achieving high-performance in Angular applications often relies on understanding and optimizing change detection. Change detection refers to the process by which Angular monitors and updates the UI to reflect data changes. The default change detection strategy may suffice for many applications, but optimizing it can lead to even better performance.

In this post, we'll dive deeper into Angular's change detection mechanism and discuss advanced optimization techniques to maximize your application's performance. Buckle up for an exciting trip to deeper parts of Angular change detection!

![Angular Change Detection](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ah9vj88m5e04natki47g.jpg)

*Picture by [Gabriel Valdez](https://unsplash.com/@gabrielvdz?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText) at [Unsplash](https://unsplash.com/es/fotos/Q6-n5G2vA78?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)*

## Change Detection Optimization Strategies

### Profiling Change Detection Performance

Before optimizing change detection, it's essential to profile your application's performance to identify bottlenecks. Using tools like the [Angular DevTools](https://chrome.google.com/webstore/detail/angular-devtools/ienfalfjdbdpebioblfackkekamfmbnh) extension for Chrome, you can inspect your component tree and visualize change detection cycles and pinpoint areas that need optimization.

### Zone.js and Angular's Change Detection

![zone.js](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/e23ujtl5y1c8zn0k6x0l.jpg)
*Photo by [Enouch E:] (https://www.pexels.com/photo/a-yellow-clear-zone-on-asphalt-11054546/)*

So... what on earth is Zone,js? Zone.js is a library that intercepts asynchronous tasks and "notifies" Angular when tasks complete. By leveraging Zone.js, Angular can automatically trigger change detection when tasks like user interactions, timers, or HTTP requests finish. Understanding the role of Zone.js can help you fine-tune change detection, making your application more performant.

#### Zone.js Pollution and its Effects

Zone.js is designed to intercept and track all asynchronous operations in an application. However, this can sometimes lead to a phenomenon known as "Zone.js pollution," where unrelated asynchronous tasks trigger unnecessary change detection cycles, negatively impacting performance. By identifying and isolating such tasks, you can minimize the impact of Zone.js pollution on your application.


#### Using NgZone to Control Zone.js Behavior

NgZone is an Angular service that wraps Zone.js, providing a consistent interface for working with Zone.js in Angular applications. By using NgZone's runOutsideAngular() method, you can execute code outside of Angular's change detection mechanism, preventing unnecessary or redundant change detection cycles due to Zone.js pollution.

#####When should I consider this:

- Your application includes third-party libraries that use asynchronous tasks, such as analytics, charts or real-time data streaming services. These tasks may cause unnecessary or redundant change detection cycles, degrading performance.

#####Code example:
```typescript
import { NgZone } from '@angular/core';

constructor(private ngZone: NgZone) {}

// Running code outside of Angular's change detection
this.ngZone.runOutsideAngular(() => {
  // Your code here
});

```




### Improving ChangeDetectionStrategy.*OnPush*

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/0thp56sp8fl955rhi9jv.jpg)
Photo by <a href="https://unsplash.com/@huntleytography?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Devon Janse van Rensburg</a> at <a href="https://unsplash.com/es/fotos/tjVImOAspag?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Unsplash</a>
  
We know that one of the ways to improve performance in a component is using OnPush change detection strategy. We reduce the amount of things that angular needs to keep track of (namely Input changes, events oroginated from the component and observable new emissions in the async pipe, although the last one is technically a `markForCheck()` strategy) However, we can improve the performance of the OnPush strategy by following these tips to further optimize your application's performance:

####1.Debounce Input Changes
If your component receives rapid input changes, debounce the changes to reduce the number of change detection cycles triggered.

#####When should I consider this:

- Your application has input components, such as search bars or sliders, that receive rapid input changes and cause excessive change detection cycles.

#####Code Example:
```typescript
import { debounceTime } from 'rxjs/operators';

// Debouncing input changes
this.searchInput.valueChanges.pipe(
  debounceTime(300)
).subscribe(value => {
  this.search(value);
});
```



####2.Optimize Observables
Use operators like `distinctUntilChanged()` or `shareReplay()` to limit unnecessary emissions and optimize change detection cycles.

#####When should I consider this:

-Your application uses RxJS Observables extensively, and you need to ensure that only necessary emissions trigger change detection cycles. 

#####Code Example:
```typescript
import { distinctUntilChanged, shareReplay } from 'rxjs/operators';

// Using distinctUntilChanged and shareReplay operators
this.data$ = this.dataService.getData().pipe(
  distinctUntilChanged(),
  shareReplay(1)
);
```





### Other optimization strategies for smoother change detection cycles
![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/k10a7v1gy7fdomkv2zgt.jpg)
Photo by [Miguel Á. Padriñán:](https://www.pexels.com/photo/photo-of-golden-cogwheel-on-black-background-3785932/)

To further optimize change detection performance, consider the following strategies:

####1. Immutable Data: 
By using immutable data structures, you can ensure that data changes only when necessary. This can significantly reduce the number of change detection cycles, as Angular will only need to check for reference changes instead of deep object comparisons.

#####When should I consider this:
-Your application uses large data objects that frequently change, causing performance issues due to excessive deep object comparisons during change detection cycles.
#####Code Example:
```typescript
import { List } from 'immutable';

// Mutable array of objects
const mutableData = [
  { id: 1, name: 'Item 1' },
  { id: 2, name: 'Item 2' },
  { id: 3, name: 'Item 3' },
];

// Converting mutable data to an immutable List of objects
const immutableData: List<object> = List(mutableData);

console.log('Immutable data:', immutableData);

// Updating an item in the immutable data (returns a new List)
const updatedImmutableData = immutableData.set(1, { ...immutableData.get(1), name: 'Updated Item 2' });

console.log('Updated immutable data:', updatedImmutableData);
```

####2.Batch Updates: 
Accumulate multiple data changes before updating the UI, reducing the frequency of change detection cycles. This can be done by using techniques like debouncing or throttling.

####3.Using ChangeDetectorRef: 
The ChangeDetectorRef service allows you to manually mark components as needing change detection. This can be useful when working with asynchronous tasks that are not automatically tracked by Zone.js, or when using third-party libraries that operate outside Angular's change detection mechanism.

#####When should I consider this:
-Your application integrates with third-party libraries that operate outside Angular's change detection mechanism, and you need to ensure that the UI updates when the data changes.

#####Code Example:
```typescript
import { ChangeDetectorRef } from '@angular/core';

constructor(private cd: ChangeDetectorRef) {}

// Triggering change detection manually
this.cd.detectChanges();

----
// Marking a component for check
this.cd.markForCheck();
```
####4.Utilize TrackBy with *ngFor
When using *ngFor with OnPush, use the trackBy function to minimize DOM manipulation and improve performance.

#####When should I consider this:

-Your application uses *ngFor to render large lists, and you need to minimize DOM manipulation to improve performance.

#####Code Example:
```typescript
import { Component } from '@angular/core';

@Component({
  selector: 'app-list',
  template: `
    <ul>
      <li *ngFor="let item of items; trackBy: trackById">{{item.id}} - {{item.name}}</li>
    </ul>
  `
})
export class ListComponent {
  items = [
    { id: 1, name: 'Item 1' },
    { id: 2, name: 'Item 2' },
    // ...
  ];

  trackById(index: number, item: any): number {
    return item.id;
  }
}

```



##Conclusion:

Mastering Angular's change detection strategies is vital for building high-performance applications. By understanding the intricacies of Angular's change detection mechanism and implementing advanced optimization techniques, you can significantly enhance your application's performance. 

Finally if you have any questions or suggestions feel free to show up and comment!