Should navigating to the current URL preserve history.state?

[domenic]

Spinning off from #6197 (comment).

Test page: https://boom-bath.glitch.me/session-history-2.html

1. Press "Set history.state to 'foo'"
2. Then press any of the other three four buttons/links.

Results:

• Firefox: location.reload() retains history.state. All other mechanisms clear it.
• Chrome: history.state is always retained.
• Safari: ???

Also of note: both browsers agree that overall document scroll position is retained on location.reload() and cleared otherwise. Chrome, however, clears the textbox scroll position and its value (if updated) in all cases, including location.reload(); Firefox retains those pieces of data in location.reload().

At a spec level, discussed a bit in #6197 (comment), we have several distinguishable actions:

• (X) Navigate normally to the same URL as the current URL
• (Y) Navigate with replacement (location.replace()) to the same URL as the current URL
• (Z) Navigate with reloading (location.reload()) to the same URL as the current URL

and we have the following potential behaviors:

• (A) Keep the current session history entry. Just replace its document.
• (A') Keep the current session history entry. Replace its document and maybe reset a few other things.
• (B) Throw away the current session history entry. Create a new one with a new document, the same URL, and defaults for everything else.
• (B') Remove the current session history entry. Create a new one with a new document, the same URL, and potentially copy over some of the other stuff from the old one.

So from I can see:

• Firefox performs (A) or maybe (A') for (Z), but performs (B) for (X) and (Y).
• Chrome performs (B') for (X), (Y), and (Z), copying over at least history.state, but not copying over most scroll positions. It does copy over the main document scroll position for case (Z).

I'm not sure what the best behavior is here. At a spec level, the simplest thing would be (B) for all cases (X), (Y), and (Z), but that matches no browsers. This is all complicated by the fact that the other pieces of a session history entry are harder to test and in some cases not totally specified.

/cc @natechapin @smaug----

[domenic]

In another venue @rakina notes that Chrome's comparison is between does not compare the URL that started the navigation with the browsing context's active document's URL, but instead compares the final URL of the navigation to the browsing context's active document's URL. Also, Chrome ignores fragments.

Fortunately, after #6476, the red XXX box talking about sometimes copying over the state also compares the final URL (i.e., the URL of newDocument) to the browsing context's active document's URL (i.e., the URL of sessionHistory's current entry that is about to be replaced). So the XXX box is getting closer to at least one browser, which is nice.

[rakina]

I tested this out with a modified version of Domenic's test above. I checked history.state, history.scrollRestoration, and the scroll offset of the viewport/tab and textarea

No fragment (sameurl.html -> sameurl.html)

Same-URL nav type	Creates new document	Keeps history.state, history.scrollRestoration	Keeps viewport scroll offset	Keeps textarea scroll offset
location.reload()	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Firefox
location.href = location.href	Chrome, Firefox, Safari	Chrome, Safari
location.replace(location.href)	Chrome, Firefox, Safari	Chrome, Safari
URL bar enter	Chrome, Firefox, Safari	Chrome, Safari	Chrome
Browser UI reload	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Firefox

With fragment (sameurl.html#bottom -> sameurl.html#bottom)

Same-URL nav type	Creates new document	Keeps history.state & history.scrollRestoration	Keeps viewport scroll offset	Scrolls to fragment	Keeps textarea scroll offset
location.reload()	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Chrome, Firefox, Safari		Firefox
location.href = location.href		Chrome, Safari		Chrome, Firefox, Safari
location.replace(location.href)		Chrome, Safari		Chrome, Firefox, Safari
URL bar enter	Chrome, Safari	Chrome, Safari	Chrome	Firefox, Safari
Browser UI reload	Chrome, Firefox, Safari	Chrome, Firefox, Safari	Chrome, Firefox, Safari		Firefox

Reloads

• Chrome, Firefox, Safari restores history.state,history.scrollRestoration, viewport offset on reload.
• Only Firefox restores the textarea offset on reload.
• Chrome treats URL bar navigation to the same URL as reloads (but that's out of scope of spec).

Same-URL navigations

• Script-initiated same-URL navigations will create a same-document navigation if the URL has fragment, and load a new document otherwise.
• Chrome & Safari keeps history.state & history.scrollRestoration on all same-URL navigation.

General

• Chrome, Firefox, Safari replaces the previous entry on reloads and same-URL navigations (even for the same-document case).
• Not sure how to check the other session history attributes. I guess browsing context name can be checked via WPT, but that seems to have its own set of problems.

I think since Chrome & Safari behaves the same way, maybe it makes sense to copy history.state & history.scrollRestoration on same-URL navigations. Or maybe it's weird to do that but not restore the scroll offsets too?

[domenic]

Thanks for continuing the investigation Rakina!

Not sure how to check the other session history attributes. I guess browsing context name can be checked via WPT, but that seems to have its own set of problems.

I think we should spend a small amount of time on this. If writing tests is easy, and it aligns well with other pieces of state (e.g. is always copied over in the same way as history.state), then let's try to make sure it's specced and tested well. If it's too hard to write tests for, or gives weird results due to how it interacts with other parts of the system, then we can set it aside.

I think since Chrome & Safari behaves the same way, maybe it makes sense to copy history.state & history.scrollRestoration on same-URL navigations.

Agreed.

Or maybe it's weird to do that but not restore the scroll offsets too?

Could we restore the scroll offsets too? Everyone seems to restore the viewport scroll offset according to your table above. And we can say that the lack of consistency for textarea scroll offset restoration is down to the "may" clause in https://html.spec.whatwg.org/multipage/browsing-the-web.html#restore-persisted-state .

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Note that once we get this more solid, especially if we copy over most (all?) of the fields, the next natural question will be whether we should maintain the distinction between the "entry update"/"reload" case and the "replace" case in https://html.spec.whatwg.org/#update-the-session-history-with-the-new-page . Maybe we can merge them. But figuring out the full consequences of that will be tricky, so my instinct is to wait and tackle it after we improve the spec for the "replace" case, like we're doing here.

[domenic]

@rakina, do you think you'd be able to help with web platform tests for this? I'd love to get this spec issue resolved.

[jakearchibald]

Here's another fun one:

1. Navigate to /a.
2. pushState({}, '', '').
3. Browser UI reload, but server redirects to /b.

Chrome, Safari, Firefox: history.state is null.

1. Navigate to /a.
2. pushState({}, '', '').
3. Browser UI reload, but server redirects to /a.

Firefox: history.state is null.
Chrome, Safari: history.state is retained.

1. Navigate to /a#foo.
2. pushState({}, '', '').
3. Browser UI reload, but server redirects to /a (the hash is still retained in the browser).

Firefox, Safari: history.state is null.
Chrome: history.state is retained.

The correlates with the findings in #6680, including "I have no idea what Safari is doing".