[whatwg] Do we really need history.clearState()?

[Justin Lebar]

As I alluded to in the thread "AJAX History Concerns," I'm not
convinced that we need the history.clearState() function.

I haven't been able to come up with a compelling case where a page
would use this.  I guess the idea is that I'm on Google Maps, which is
using pushState to make a history entry every time I scroll the map.
If I scroll around a lot, it might clobber my history and make it hard
to go back to the page I was at before I began looking at the map.
But it could be nice and at some point (possibly triggered by some
user action) call clearState.  Then I'd be able to click "back" and
actually go back to the Document I was previously viewing.

clearState as it exists doesn't match this use case particularly well.
 If we were concerned about clobbering history, we'd probably want to
keep the two or three newest history entries and throw out all the
rest of them.  If you were really clever, you might be able to
accomplish this by calling clearState and then using pushState to
reconstruct the part of the history you want to keep.  But getting the
URLs right would be pretty tricky, especially if clearState took you
to the last entry for the document, as currently specified.

clearState is also useless if you don't use this single-document
pushState model for your site.  If we think clearing the history is
useful for AJAX pages, I'm not sure why it wouldn't be useful for a
web application which loads multiple documents.

I think the use case I proposed is much better served by something
like history.truncate(numBefore, numAfter), which would remove all but
the numBefore entries before the current entry and the numAfter
entries after the current entry.  We'd subject this to the same-origin
policy, of course, and stop removing entries in a direction as soon as
we encountered an entry from another origin.

I'm not sure if history.truncate() is a good idea -- do we really want
to give pages that kind of control over the history? -- but at least I
can actually imagine a page using it.

Perhaps a better idea is leaving this whole issue to the UA, which
could collapse all the entries from a single origin in the UI.  Then
we wouldn't need either function.

-Justin