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conformance · v152
v152 · user-agent-image-replacement-api — conformance probe
6 assertions drawn from the spec. Each is a single contract the spec text makes. Pass/fail reflects what this browser executed; blocked means the contract was not run because it needs user mediation, hardware, or another unavailable precondition. Open the page in Chrome stable / canary / Firefox / Safari to compare.
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pass
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| id | contract | kind | verdict | detail |
|---|---|---|---|---|
htmlimageelement-exists |
The interface the proposal extends. spec ↗ | typeof | … | |
the-detection-technique-works |
The control every other assertion here depends on: an inherited handler property must be findable on an element, and an invented one must not. A prototype-only check would miss every handler an image already has, since HTMLImageElement declares none of its own. spec ↗ | script | … | |
replacedbyuseragent-exists |
The feature test the proposal specifies: a read-only boolean saying whether the element is currently showing substitute content. It reflects state, so it exists whether or not a replacement is happening. spec ↗ | script | … | |
both-event-handlers-exist |
The two reflected handlers. Both are needed: a page that learns about the start and not the end restores nothing, and one that learns about the end and not the start never adapted in the first place. spec ↗ | script | … | |
listeners-for-unknown-events-are-harmless |
A page can attach both listeners unconditionally, because addEventListener accepts any name and an event that never fires costs nothing. That is what lets the adaptation code ship without a feature branch around it. spec ↗ | script | … | |
an-image-reveals-nothing-else-about-its-pixels |
The argument for the feature, asserted as a contract: the observable properties of a loaded image describe what was requested, not what is displayed. src, currentSrc and complete are all about the request — so if they could change under a replacement, a page would have a cheaper way to notice than an event. spec ↗ | script | … |