[whatwg] history.pushState() and replaceState()'s title parameter

[Justin Lebar]

Safari 5 and Chrome 5 recently shipped the history.pushState and
replaceState methods.  Firefox 4 will also include those methods when
it ships.

pushState and replaceState take three arguments: An opaque data
object, a title, and an optional URL.  Currently, Safari and Chrome
both ignore the title parameter.

Jonas Sicking <jonas at sicking.cc> and I have been talking with Brady
Eidson <beidson at apple.com> and Darin Fisher <darin at chromium.org>,
about what we can do to clean up this API, since having an unused
parameter in our brand-new functions is unfortunate.

Ideally, we might change the pushState and replaceState methods
themselves, perhaps changing them so they only take a URL and an
optional data object.  But since Chrome and Safari have already
shipped the method, and since we hear that the functions are already
being used on the web, it's probably too late to add or remove
arguments from the functions.

It seems that the intent of the spec as it stands is that the title
parameter should show up in the session history list (shown e.g. when
you click the down arrow next to the forward button), but not in the
application's title bar.  We think this is confusing (as evidence,
observe that two browsers skipped this step!) and adds a lot of
complexity for a small amount of gain, so we're not in favor of this
approach.  If modifying the document's title in the session history
list is a desirable feature, then we could expose that property to the
DOM just as we expose document.title.

Seeing as we're stuck with the title argument in pushState and
replaceState, we propose that it modify document.title in an intuitive way:

* Before we unload a history entry, we save document.title into the
history entry.
* When we activate a history entry, we set document.title to the value
stored in the history entry.
* When we pushState, we set document.title to the title parameter
after activating the new history entry.
* When we replaceState, we set document.title to the title parameter.

In the last two cases, if the title parameter is empty, we leave
document.title unchanged.

We think this is a good compromise between complexity and functionality.

-Justin