Add an incubation update

Author: domenic

2021-11-04-incubation-update.md

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+# Incubation Update: November 4, 2021
+
+App history is starting to achieve its final form! Read on to find out what's new since [last time](./2021-06-28-incubation-update.md).
+
+## Prototype implementation and origin trial
+
+The app history implementation in Chromium recently hit an important milestone. In addition to being available behind the Experimental Web Platform features flag, it is now available as an [origin trial](https://github.com/GoogleChrome/OriginTrials/blob/gh-pages/developer-guide.md)! From Chromium versions 96–99, you can add a HTTP header or `<meta>` tag to your site to try out app history in production, against real users. [Sign up and get a token](https://developer.chrome.com/origintrials/#/view_trial/2347501305766871041) if you're ready to start experimenting!
+
+At this point we believe all of the core API is ready, giving parity with `window.history` and, due to the `dispose` event, even exceeding it. You can see an update-to-date account of our progress in the [implementation plan document](https://docs.google.com/document/d/1vmxjUzn7qccn9xwVoIKRKVEPrIstrPzztg0chlgLAMY/edit#), but to summarize the stuff that's missing as of the time of this writing:
+
+* Stop/reload/loading spinner integration with the promises passed to `event.transitionWhile()` (in progress, but not yet landed)
+* Integration with accessibility technology
+* `appHistory.transition.finished` and `appHistory.transition.rollback()`
+* `AppHistoryEntry` events besides `dispose`, i.e. `navigateto`, `navigatefrom`, and `finish`
+* The `dispose` event for cases besides forward-pruning, e.g. when the user clears their history
+* [Performance timeline integration](./README.md#performance-timeline-api-integration)
+
+We look forward to hearing about what you can build with app history. If you're running a site that might use app history, or maintaining a router library or framework, now is a great time to play around with the API, and get in touch with any feedback.
+
+(By the way, if you use TypeScript, we now host [TypeScript definitions for the API](https://github.com/WICG/app-history/blob/main/app_history.d.ts) in this repository!)
+
+## Design updates
+
+Since last time, we've made the following substantial changes:
+
+* Added `appHistory.updateCurrent()`, for specific use cases where you need to update app history state in response to a user action: [#146](https://github.com/WICG/app-history/pull/146)
+* Added back the `currentchange` event, for when `appHistory.current` changes: [#171](https://github.com/WICG/app-history/pull/171)
+* Added `key`, `id`, and `index` to `navigateEvent.destination` for `"traverse"` navigations: [#131](https://github.com/WICG/app-history/pull/131)
+* Changed the return values of all the navigating methods from just a promise, to a pair of `{ committed, finished }` promises: [#164](https://github.com/WICG/app-history/pull/164)
+* Renamed `navigateEvent.respondWith()` and `navigateEvent.canRespond` to `transitionWhile()` and `canTransition`: [#151](https://github.com/WICG/app-history/pull/151)
+* Renamed the `navigateInfo` option to just `info`: [#145](https://github.com/WICG/app-history/pull/145)
+* Started firing the `navigate` event for all traversals, but making it non-cancelable for now: [#182](https://github.com/WICG/app-history/pull/182)
+* Disabled most of the API for opaque-origin pages: [#169](https://github.com/WICG/app-history/pull/169)
+
+## The road toward shipping?
+
+As mentioned above, at this point we believe the core API is ready to experiment with, including in production evironments using origin trials or similar time-limited measures. What remains for us to do, before we could consider shipping the API?
+
+We've collated a list of ["Might block v1"](https://github.com/WICG/app-history/milestone/1) issues on the issue tracker. Most of them are related to things that, if we changed them after shipping, could cause compatibility problems: so, we need to figure them out, and finalize the spec/implementation/tests. This includes the still-ongoing [API naming discussion](https://github.com/WICG/app-history/issues/83) 😅. If all goes well, including reviews with other browsers, it's conceivable we could solve these issues in time for Chromium 100 in March 2022.
+
+That list is just the bare minimum, however. Based on feedback from developers and other browser vendors, a few other things are on our radar as high priority, which we might try to finish up before the initial release or at least shortly afterward:
+
+* Updating, deleting, and rearranging non-current entries is a common developer pain point, with solid use cases: [#9](https://github.com/WICG/app-history/issues/9)
+* Canceling browser UI-initiated back/forward navigations, to implement "are you sure you want to leave this page?", is technically difficult but definitely planned: see [#32](https://github.com/WICG/app-history/issues/32) and also some discussion in [#178](https://github.com/WICG/app-history/issues/178)
+* Ensuring `appHistory.navigate()` has parity with `<a>` by adding download, form data, and referrer policy options, would not be hard and would round out the API nicely: [#82](https://github.com/WICG/app-history/issues/82)
+* Adding an easy way to do "client-side redirects" would solve a sharp edge; you can do these with the current API but it's trickier than it should be: [#124](https://github.com/WICG/app-history/issues/124)
+
+These and many other such ideas are under the ["addition"](https://github.com/WICG/app-history/labels/addition) label in the issue tracker. If any such additions would be especially helpful to your project, please let us know with either a thumbs-up or, better yet, a comment describing your use case.