[css-view-transitions-1] Defer restoring persisted state until after capturing old state #9676
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noamr
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Dec 15, 2023
When starting a view transition right before state restoration,
e.g. `addEventListener("popstate", () => startViewTransition(() => {...}))`,
according to the current spec the scroll position would be restored
before the `startViewTransition` callback is called, which means that
it would be captured as part of the old state, even though it belongs
to the new state.
This change makes it so that we defer persisted state restoration
until after the old state is captured.
Together with w3c/csswg-drafts#9676
5 tasks
domenic
reviewed
Dec 18, 2023
css-view-transitions-1/Overview.bs
Outdated
| @@ -47,6 +47,9 @@ spec:css-display-4; type: dfn; text:invisible; | |||
| urlPrefix: https://wicg.github.io/navigation-api/; type: interface; | |||
| text: NavigateEvent | |||
| text: signal; for: NavigateEvent; url: #ref-for-dom-navigateevent-signal① | |||
| urlPrefix: https://html.spec.whatwg.org/multipage/; spec: html; type: dfn; | |||
| text: restore persisted state; url: #restore-persisted-state | |||
| text: latest entry; url: #latest-entry | |||
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Instead of poking into HTML's externals, try to get whatwg/html#9996 to export the appropriate parts.
(I'm a bit scared of exporting "latest entry" though, since it's a pretty low-level detail... document's node navigable's active session history entry would be a more public API. Maybe it's the same thing in this case?)
| 1. "`pending`". | ||
| 1. "`immediate`". | ||
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| Note: this is used to defer automatic restoration of persisted state, e.g. scroll position, |
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Can you add what immediate implies as well?
| @@ -1252,10 +1267,16 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface; | |||
| If failure is returned, then [=skip the view transition=] for |transition| with an "{{InvalidStateError}}" {{DOMException}} in |transition|'s [=relevant Realm=], | |||
| and return. | |||
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| 1. [=Resolve persisted state restoration=] for |transition|. | |||
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We should do this in the skip case as well.
| @@ -1094,6 +1097,18 @@ urlPrefix: https://wicg.github.io/navigation-api/; type: interface; | |||
| Initially null. | |||
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| Note: this is used for cross-document view transitions. | |||
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| : <dfn>persisted state restoration</dfn> | |||
| :: One of the following, initially "`defer`": | |||
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Do we have scroll restoration in the spec for cross-document navigations?
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| @@ -1940,6 +1978,7 @@ Changes from <a href="https://www.w3.org/TR/2023/WD-css-view-transitions-1-20230 | |||
| * Copy `color-scheme` from DOM element to ''::view-transition-group()''. See <a href="https://github.com/w3c/csswg-drafts/issues/9276">issue 9276</a>. | |||
| * Expose [=auto-skip view transition=] for a {{Document}}, to allow having outbound cross-document transitions preceed programmatic view transiitons. see <a href="https://github.com/w3c/csswg-drafts/issues/9512">issue 9512</a>. | |||
| * Add a note about why 'view-transition-name' should be animatable. | |||
| * Export an algorithm and add mechanism to defer restoring scroll/persisted state. | |||
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Is there a link to an html or csswg issue where this was discussed?
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This fixes an issue that the spec restores the persisted state (e.g. scroll position) too eagerly, e.g. when calling
document.startViewTransitioninside apopstatehandler, not giving the UA an opportunity to first capture the old state.This exports an algorithm that should be called from the HTML spec when ready to automatically restore persisted state, e.g. after
popstate. If the algorithm returns true, proceed as normal, otherwise the state will be restored after capturing the old state.