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Build an Infinite Scroll Component in Angular


Building SPAs, we sometimes come across the need to display data using the technique of infinite scrolling — i.e., continuously loading data as the user scrolls down the page.
Ever since the Intersection Observer APIwas added to browsers, building a reusable infinite scroll component has never been easier. Let’s learn how we can create such a component using this API.
Note that we’re not going to dive into the Intersection Observer API, so if you’re not familiar with it, I recommend reading this article beforehand.

Creating the Component

The main concept is to place an observable element at the end of a list of displayed items, in order to add more data when the user reaches the bottom of that list.

@Component({
selector: 'infinite-scroll',
template: `<ng-content></ng-content><div #anchor></div>`
})
export class InfiniteScrollComponent implements OnInit, OnDestroy {
...
ngOnInit() {
const options = {
root: null,
...this.options
};
this.observer = new IntersectionObserver(([entry]) => {
entry.isIntersecting && this.scrolled.emit();
}, options);
this.observer.observe(this.anchor.nativeElement);
}
}

We add a check to see whether the current host element is a scrollable container. If it is, we set it as the rootelement.
Finally, we don’t want memory leaks in our application, so we’ll disconnect the observer when the component destroyed:
ngOnDestroy() {
this.observer.disconnect();
}

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