fix(inject-is-intersecting): Fix encapsulation, SSR safety, and shared-element subscription teardown

[endlacer]

1. observe() now returns Observable instead of exposing the internal Subject directly, preventing consumers from calling .next(), .error(), or .complete() externally
2. intersect() removed from the public interface and made private — it is an internal callback and should not be callable from outside the service
3. Added isPlatformBrowser() guard in createObserver() to prevent a ReferenceError crash in SSR environments where IntersectionObserver is unavailable
4. Added ref-counting via observerCounts so that when multiple components observe the same element, a single component being destroyed no longer completes the shared Subject and silently cuts off all other consumers
5. Fixed incorrect first argument to assertInjector (injectDestroy → injectIsIntersecting) so injection context errors report the correct origin

[gemini-code-assist]

Summary of Changes

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This pull request significantly refines the injectIsIntersecting functionality by enhancing its robustness and developer experience. The changes focus on improving encapsulation, ensuring compatibility with Server-Side Rendering, and correctly managing shared resources to prevent unexpected behavior when multiple parts of an application interact with the same observed elements. These updates lead to a more stable and predictable API.

Highlights

• Improved Encapsulation: The observe() method now returns an Observable<IntersectionObserverEntry> instead of directly exposing the internal Subject, preventing external manipulation. Additionally, the intersect() method has been made private, restricting its use to internal service logic.
• SSR Safety: A isPlatformBrowser() guard has been added to createObserver() to prevent ReferenceError crashes in Server-Side Rendering (SSR) environments where IntersectionObserver is not available.
• Robust Shared-Element Subscription Teardown: Reference counting via observerCounts has been implemented. This ensures that when multiple components observe the same element, the IntersectionObserver is only truly unobserved and disconnected when all consumers have unsubscribed, preventing premature termination of other active subscriptions.
• Corrected assertInjector Context: The first argument to assertInjector was fixed from injectDestroy to injectIsIntersecting, ensuring that injection context errors report the correct origin.

Changelog

• libs/ngxtension/inject-is-intersecting/src/inject-is-intersecting.spec.ts
  • Updated existing test calls to the intersect method to account for its new private visibility using type assertion.
  • Added comprehensive tests for the IsInViewportService to verify the new reference counting logic for observe and unobserve methods, ensuring correct behavior when multiple components observe the same element.
• libs/ngxtension/inject-is-intersecting/src/inject-is-intersecting.ts
  • Replaced injectDestroy import with Observable from rxjs.
  • Modified injectIsIntersecting to return an Observable instead of a Subject, enhancing encapsulation.
  • Corrected the first argument in assertInjector from injectDestroy to injectIsIntersecting for accurate error reporting.
• libs/ngxtension/inject-is-intersecting/src/is-in-viewport.service.ts
  • Introduced PLATFORM_ID and isPlatformBrowser to prevent IntersectionObserver errors in SSR environments.
  • Implemented a reference counting mechanism (observerCounts) to manage shared IntersectionObserver instances, ensuring that an element is only unobserved when all consumers have unsubscribed.
  • Changed the observe method to return an Observable instead of directly exposing the internal Subject, enhancing encapsulation.
  • Made the intersect and disconnect methods private to restrict external access.
  • Updated the IsInViewportServiceInterface to reflect the new observe return type and the removal of intersect from the public interface.

Activity

• No human activity has occurred on this pull request yet.

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☁️ Nx Cloud last updated this comment at 2026-03-28 19:29:36 UTC

[gemini-code-assist]

Code Review

This pull request introduces several important fixes and improvements to inject-is-intersecting. The changes correctly address encapsulation by returning an Observable instead of a Subject and making internal methods private. SSR safety is improved by adding a platform check before using IntersectionObserver. The introduction of reference counting for element observers is a great fix to prevent premature teardown when an element is shared. The tests have been updated accordingly, and a new test suite for the reference counting logic has been added, which is excellent. I have one suggestion to improve the robustness of the unobserve method's logic.

[endlacer]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces several excellent improvements to inject-is-intersecting, including fixes for encapsulation, SSR safety, and subscription teardown logic using reference counting. The changes are well-implemented and include corresponding tests for the new logic. I've suggested a minor refactoring in IsInViewportService to improve code clarity. Overall, this is a great set of improvements.