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IntersectionObserver

Reports when observed elements enter or leave the viewport or a root element. Specification: w3c.github.io/IntersectionObserver/.

Results​

Probed on 2026-10-19 with Node.js v22.23.3.

warpdom 0.1.6​

Missing

Not defined in this engine's window.

Web IDL existence (coverage):

Report a wrong result for warpdom

happy-dom 21.0.3​

Stub

0 of 2 checks work.

Web IDL existence (coverage):

  • IntersectionObserver: interface present; 4 of 10 members present, missing: root, rootMargin, scrollMargin, thresholds, delay, trackVisibility.

  • A new observer has root null, rootMargin "0px 0px 0px 0px" and thresholds [0]. Intersection Observer §2.2: root is "null if none was provided"; rootMargin: "If no rootMargin was passed to the IntersectionObserver constructor, the value of this attribute is '0px 0px 0px 0px'"; §3.2.1 (initialize a new IntersectionObserver): "If thresholds is empty, append 0 to thresholds."

    • Result: root: expected null, got undefined

  • Observing a connected element delivers an initial entry for it with an isIntersecting boolean, whether or not it intersects. Intersection Observer §3.2.2 (observe a target Element) registers it with "a previousThresholdIndex property set to -1"; §3.2.10 (update intersection observations) computes a thresholdIndex of 0 or more and "If thresholdIndex does not equal previousThresholdIndex … queue an IntersectionObserverEntry". HTML runs these steps in "update the rendering", and §3.4.2 forbids skipping that update while a target has had no entry yet.

    • Result: no entry delivered (waited 500 ms)
Report a wrong result for happy-dom

jsdom 30.1.3​

Missing

Not defined in this engine's window.

Web IDL existence (coverage):

Report a wrong result for jsdom

linkedom 0.18.13​

Missing

Not defined in this engine's window.

Web IDL existence (coverage):

Report a wrong result for linkedom

Checks​

  • defaults: A new observer has root null, rootMargin "0px 0px 0px 0px" and thresholds [0]. Intersection Observer §2.2: root is "null if none was provided"; rootMargin: "If no rootMargin was passed to the IntersectionObserver constructor, the value of this attribute is '0px 0px 0px 0px'"; §3.2.1 (initialize a new IntersectionObserver): "If thresholds is empty, append 0 to thresholds." (spec)
  • initial-notification: Observing a connected element delivers an initial entry for it with an isIntersecting boolean, whether or not it intersects. Intersection Observer §3.2.2 (observe a target Element) registers it with "a previousThresholdIndex property set to -1"; §3.2.10 (update intersection observations) computes a thresholdIndex of 0 or more and "If thresholdIndex does not equal previousThresholdIndex … queue an IntersectionObserverEntry". HTML runs these steps in "update the rendering", and §3.4.2 forbids skipping that update while a target has had no entry yet. (spec)

Working around it in tests​

Tests usually replace it with a mock class (for example the "react-intersection-observer/test-utils" helpers or a hand-written stub).