Bug 194938 – Changing the transition-duration of an-flight transition should not alter or cancel it

• Status: NEW
• Component: Animations

[Antoine Quint]

Created attachment 362706 [details]
Test case

See the attached test case. In this example we start a transition by setting transition-duration to a positive value and then setting a "margin-left" style which triggers a transition for the duration set. Then, one second after the transition has started, we remove the transition-duration which reverts back to 0. In our current implementation this cancels the transition, but the spec says that it shouldn't, per the note at the bottom of https://drafts.csswg.org/css-transitions-1/#starting:

"Note that once the transition of a property has started (including being in its delay phase), it continues running based on the original timing function, duration, and delay, even if the transition-timing-function, transition-duration, or transition-delay property changes before the transition is complete. However, if the transition-property property changes such that the transition would not have started, the transition stops (and the property immediately changes to its final value)."

While this is informative text, there are no normative steps that would indicate otherwise.

[Radar WebKit Bug Importer]

<rdar://problem/48305929>