Retrieve the attribute from the element that is in the active state

I'm facing a challenge in determining the active status of an element attribute. I attempted the following approach, but it incorrectly returned false even though the element had the attribute in an active state - (.c-banner.active is present)

During ngAfterViewInit() {
    const bannerElement = document.getElementById("banner");
    const isActiveState = bannerElement && bannerElement.getAttribute("class")
      .indexOf("c-banner.active") !== -1;  // This resulted in false
}

Answer №1

Have you considered utilizing the classList and its contains method?

classList.contains();

 ngAfterViewInit() {
    const bannerElm = document.getElementById("banner");
    const isActive = bannerElm && bannerElm.classList.contains('c-banner') && bannerElm.classList.contains('active');
}

Answer №2

To determine if the element contains the active class, you can utilize the classList.contains method.

ngAfterViewInit() {
    setTimeout(() => {
        const isActive = bannerElm &&
                         bannerElm.classList.contains('c-banner') &&
                         bannerElm.classList.contains('active');
    }, 1000);
}

[UPDATED] By enclosing it within a setTimeout(), the issue with component initialization orders was resolved! This solution may help those facing similar challenges.

Answer №3

Aside from the traditional method of accessing the value of the class attribute, it seems that the issue at hand is related to asynchronous behavior based on your remarks. Instead of resorting to a makeshift setTimeout fix, my suggestion would be to implement a mutation observer and respond to attribute changes accordingly. Here's a sample approach to tackle this.

PS: I have adjusted the response to better align with your goals. Ultimately, this adjustment may not have a significant impact, except in cases where the banner state changes before the debounce period elapses, resulting in immediate emission and potential time savings compared to using setTimeout.

bannerIsActive$ = new BehaviorSubject<boolean>(false);

ngAfterViewInit() {
    const banner = document.getElementById('banner');

    const observer = new MutationObserver((mutations: MutationRecord[]) => {
        const mutation = mutations[0];
        const classList: DOMTokenList = mutation.target['classList'];
        this.bannerIsActive$.next(mutation.attributeName === 'class' && classList.contains('active'));
    });

    observer.observe(banner, {
        attributes: true
    });

    this.bannerIsActive$.pipe(
         debounce(isActive => timer(isActive ? 0 : 1000)),
         take(1)
    ).subscribe(isActive => {
       // perform actions based on the banner state
    });
}

Answer №4

It is recommended to utilize ViewChild instead of directly accessing your DOM elements. Both methods will achieve the desired outcome, but using ViewChild is considered the best practice.

@ViewChild('banner') input; 
ngAfterViewInit() {
    var classAttributes= this.input.nativeElement.getAttribute('class');
    var result = classAttributes && classAttributes.includes('c-banner');
}

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