Angular 18: How to Ensure ngAfterViewInit Fires without zone.js in OnPush Components

Welcome to the world of Angular 18, where the quest for performance optimization has led us to rethink our approach to change detection. With the introduction of Ivy and the deprecation of zone.js, we need to find new ways to ensure that our components behave as expected. In this article, we’ll dive into the mysteries of ngAfterViewInit and explore how to make it fire without zone.js in OnPush components.

The Problem: ngAfterViewInit Not Firing in OnPush Components

If you’re using Angular 18 with Ivy and have migrated your components to use the OnPush change detection strategy, you might have noticed that ngAfterViewInit is not firing as expected. This can be frustrating, especially if your component relies on this lifecycle hook to perform critical initialization tasks.

The reason for this behavior lies in the way OnPush components handle change detection. By default, OnPush components only detect changes when the inputs change, which means that ngAfterViewInit might not be triggered automatically.

Understanding Change Detection in Angular 18

In Angular 18, change detection is handled by the Ivy engine, which uses a different approach to detecting changes compared to the previous versions. Ivy uses a concept called “tick,” which is a mechanism that checks for changes in the component tree.

The tick process is responsible for detecting changes in the following scenarios:

• When the component’s inputs change
• When the component’s properties change
• When the component’s DOM is mutated

In the case of OnPush components, the tick process is only triggered when the inputs change. This means that if you’re relying on ngAfterViewInit to perform initialization tasks, you might need to take extra steps to ensure that it fires.

Solution 1: Use the detectChanges Method

One way to ensure that ngAfterViewInit fires in OnPush components is to use the detectChanges method provided by the ChangeDetectorRef class. This method forces the change detector to detect changes and run the change detection cycle.

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

@Component({
  selector: 'app-example',
  template: '
Example Component
',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ExampleComponent implements AfterViewInit {
  constructor(private cdRef: ChangeDetectorRef) { }

  ngAfterViewInit(): void {
    console.log('ngAfterViewInit fired!');
    this.cdRef.detectChanges();
  }
}

In this example, we inject the ChangeDetectorRef instance into our component and call the detectChanges method in the ngAfterViewInit lifecycle hook. This forces the change detector to detect changes and run the change detection cycle, ensuring that ngAfterViewInit fires.

Solution 2: Use the markForCheck Method

Another way to ensure that ngAfterViewInit fires in OnPush components is to use the markForCheck method provided by the ChangeDetectorRef class. This method marks the component as needing to be checked for changes, which triggers the change detection cycle.

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

@Component({
  selector: 'app-example',
  template: '
Example Component
',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ExampleComponent implements AfterViewInit {
  constructor(private cdRef: ChangeDetectorRef) { }

  ngAfterViewInit(): void {
    console.log('ngAfterViewInit fired!');
    this.cdRef.markForCheck();
  }
}

In this example, we call the markForCheck method in the ngAfterViewInit lifecycle hook, which marks the component as needing to be checked for changes. This triggers the change detection cycle, ensuring that ngAfterViewInit fires.

Solution 3: Use a Timer

A more hacky approach to ensure that ngAfterViewInit fires in OnPush components is to use a timer. By using a timer, we can delay the execution of the code in ngAfterViewInit until the change detection cycle has completed.

import { Component, OnPush, AfterViewInit } from '@angular/core';

@Component({
  selector: 'app-example',
  template: '
Example Component
',
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class ExampleComponent implements AfterViewInit {
  ngAfterViewInit(): void {
    setTimeout(() => {
      console.log('ngAfterViewInit fired!');
    }, 0);
  }
}

In this example, we use the setTimeout function to delay the execution of the code in ngAfterViewInit until the change detection cycle has completed. This ensures that ngAfterViewInit fires as expected.

Conclusion

In this article, we explored the issue of ngAfterViewInit not firing in OnPush components in Angular 18. We discussed the reasons behind this behavior and provided three solutions to ensure that ngAfterViewInit fires as expected.

By using the detectChanges method, markForCheck method, or a timer, you can ensure that your OnPush components behave as expected and that ngAfterViewInit fires without relying on zone.js.

Remember, when working with OnPush components, it’s essential to understand how change detection works in Angular 18 and take the necessary steps to ensure that your components behave as expected.

Solution	Description
detectChanges method	Forces the change detector to detect changes and run the change detection cycle
markForCheck method	Marks the component as needing to be checked for changes, triggering the change detection cycle
Timer	Delays the execution of the code in ngAfterViewInit until the change detection cycle has completed

We hope this article has been helpful in resolving the issue of ngAfterViewInit not firing in OnPush components in Angular 18. If you have any questions or need further assistance, feel free to ask!

Happy coding!

Here is the FAQ section on “Angular 18: How to Ensure ngAfterViewInit Fires without zone.js in OnPush Components”:

Frequently Asked Question

Get the inside scoop on making ngAfterViewInit work its magic without zone.js in OnPush components!