Intent to Deprecate and Remove: Shadow DOM V0, Custom Elements V0, HTML Imports
Hayato Ito
Primary eng (and PM) emails
hay...@chromium.org, ko...@chromium.org, yoi...@chromium.org,
Summary
Remove Shadow DOM V0, Custom Elements V0, and HTML Imports at once in April, 2019 after deprecation period. All these pre-V1 era web components technologies except HTML Templates were not adopted by any other rendering engines. We discourage any usage of these APIs and encourage migrating to V1 APIs and ES modules.
We are targeting M73 which will be on the stable channel in April 2019 to disable the features. Just in case people need more time for migration, we plan to provide an option of using origin trials to keep using the APIs, see below for details.
Here is the timeline.
2018Q2 (done)
Reach out Chrome internal users (e.g. WebUI)
Analyze log data (UKM etc.) to identify non-polyfilled users
2018Q3
Start showing deprecation message on dev channel (M70)
Proactively drive the usage down
2018Q4
Start showing deprecation message on stable channel (M70)
Continue driving the usage down
2019Q1
Disable the feature in M73 (branch Jan. 2019)
2019Q2
Feature disabled in stable, start reverse origin trials for remaining users
2020Q1
Stop accepting origin trials
2020Q2
Remove the code from the code base
Motivation
Shadow DOM V0, Custom Elements V0, and HTML Imports were launched in 2014, but they did not get adopted by other browser engines. Instead, Shadow DOM V1, Custom Elements V1, and ES modules are widely adopted by various browser engines today. Chrome has shipped Shadow DOM V1 / Custom Elements V1 in 2016 and ES modules in 2017.
This is the second intent, the first one was to deprecate only Shadow DOM V0 in Nov. 2016 after Shadow DOM V1 shipped. We withheld deprecating mostly because we had not analyzed the usage at that time.
Since then, we
identified the most major users of Shadow DOM V0 and reached out to them (AdBlock Plus, AdBlock) , and helped them moving away from Shadow DOM V0, which resulted in significant usage drop (14% to 2% - considering the usage was 2.2% at the previous intent post with a different measurement method than today, current 2% corresponds to ~0.3% at that time).
reached out Chrome internal users (e.g. Chrome WebUI used V0 APIs via Polymer V1) to migrate to V1 APIs (or Polymer V2+), tracked at crbug.com/806159. Half of them are done, and the rest have plan to meet the timeline.
removed features of Shadow DOM V0 which are not available in V1 (/deep/, multiple shadow roots) to facilitate web developers to migrate from Shadow DOM V0 to V1.
migrated Blink’s UA shadow implementation from V0 to V1.
shipped type extension (aka “is=” attribute) for Custom Elements V1, for Custom Element V0 users to migrate to V1
Opted in UKM for better analysis of which sites are using these APIs
Analyzed httparchive data to identify list of sites that use the APIs
Since then, we also found that in many real-world use cases, Shadow DOM V0, Custom Elements V0, HTML Imports were used together, and instead of getting each of them migrated respectively, getting all of them migrated to today’s standards at once, or at least use the polyfill would make it less troublesome, easier to migrate, rather than fighting with every edge case of combination of polyfill and native implementation.
We found cases that some sites use browser sniffing to assume if it is “Chrome”, use native Custom Elements V0 and HTML Imports, and other sites once feature detect Shadow DOM V0, they assume Custom Elements V0 and HTML Imports are also available. The former can’t be helped, but the latter can be saved by one-off deprecation strategy.
Note: the polyfill (webcomponentsjs) is designed to feature-detect and polyfill any combination of Shadow DOM V0, Custom Elements V0, HTML Imports. Having said that, each has its own implementation limitation and different level of fidelity to native implementation, if we go the route of one-by-one deprecation, every site owner has to extensively test the site, while if we deprecate and remove at once, assuming the original site is designed to work for both Blink-based and non-Blink-based browsers using the polyfill, the probability that the site continues to work without any modification must be very high.
Compatibility and Interoperability Risk
No other browser engines support Shadow DOM V0, Custom Elements V0, and HTML Imports.
Existing users of these APIs are mainly coming from Polymer V1 users (Shadow DOM V0, Custom Elements V0, and HTML Imports) and Polymer V2 users (HTML Imports only, Shadow DOM and Custom Elements are V1). Fortunately for them, the impact should be minimal at the removal because these features are polyfilled and those pages should continue to work. Therefore even though their current usages via UMA look high, we can ignore the major portion of it (see below for details). We continue to figure out more exact usage of non-polyfilled sites that will break via various sources (UMA, UKM, httparchive, …).
Most of Chrome internal usage (such as Chrome Web UI) has migration plans and it is tracked at crbug.com/806159.
Note: even though Event.path was originally defined with Shadow DOM V0, and is superseded by Event.composedPath() in the V1 spec, Event.path can work without Shadow DOM V0 and will be deprecated separately.
Edge/IE: Not supported
Firefox: Not supported
Safari: Not supported
Alternative implementation suggestion for web developers
The most straightforward option is to migrate to Shadow DOM V1, Custom Elements V1, ES modules respectively at once. For Shadow DOM V1, there’s a document to compare V0 and V1 APIs. As this is not a simple replacement of APIs, it may be time consuming.
If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as “webcomponentsjs”. Specifically for polyfilling V0 APIs, you can use its v0 branch. There are other alternative polyfills for each, like AshleyScirra’s HTML Imports polyfill.
If you use Polymer V1 or V2, in most cases you do not have to take any action because the polyfill should kick in where these APIs are not available. If you would like to try if the polyfill works, you can pass --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome (see howto document for passing command line parameter). To be more future proof, it is a good idea to migrate to a newer version of Polymer, see their document for upgrading to 3.0 and 2.0.
Note: at this moment Chrome’s devtools use Shadow DOM V0 and Custom Elements V0, if you pass the option above, you cannot open developer tools. In that case you can use remote debugging.
If you are an owner/developer of a site where any options above does not help, and cannot have time to do the work by the expected deadline (April 2019), we plan to offer an option to use origin trials to opt-in for the site to enable deprecated features for up to 1 year. Origin Trials are a mechanism that a site owner can apply for using Chrome’s experimental features, by getting a token to embed in a page to unlock the features. We use this for allowing to use deprecated features, aka “reverse origin trials”. How to apply for this will be sent out separately, when the removal date approaches (expecting in Jan 2019).
If you encounter a site that you do not own, but is broken due to this deprecation, you can try passing --enable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome. This will work until we remove the code in 2020.
Usage information from UseCounter
Element.createShadowRoot() (representative for Shadow DOM V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/456 (~1.7%)
According to internal per-OS breakdown data, Android is the lowest (~0.85%) and other desktop OSes are all higher than 1.7%. It could mean that still some extensions use this. On httparchive mobile sites, we have only ~260 URLs out of Alexa 500,000 top mobile sites (~0.45%, because UMA takes page views into account, number % of top URLs must be smaller than UMA). By reaching out non-polyfilled sites we think we can reduce the pageview-based number of non-polyfilled sites to below 0.1% within this deprecation period.
Document.registerElement() (representative for Custom Elements V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/457 (~5.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. We have been talking with YouTube team. From internal UMA per-OS breakdown, Android is ~3.8% (and other desktop OSes are above 5%). We have ~4000 URLs in httparchive for mobile sites (~0.8%), and will pick up non-polyfilled sites and reach them out. Even for non-polyfilled sites, unless they run Blink-based browser only sites, we assume most of them feature-detect with some fallback, therefore problematic sites should be very few (to be closely analyzed, though).
HTML Imports (<link rel=”import”>)
https://www.chromestatus.com/metrics/feature/timeline/popularity/455 (~2.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. From internal UMA per-OS breakdown, Android is ~0.13% (and other desktop OSs are above 2%). Once YouTube desktop move out of HTML Imports, desktop numbers should become closer to Android’s. From httparchive mobile sites, ~280 URLs (out of 500,000 - ~0.6%) pmeenan@ already looked at these list and 175 out of 277 are identified using web components polyfill. So ~100 sites out of 500,000 sites will be affected by this, which is ~0.02% of sites.
Polymer V1 (detected by “dom-module” registration via document.registerElement)
https://www.chromestatus.com/metrics/feature/timeline/popularity/2466 (~1.9%)
This includes desktop YouTube usage (Note: this counter is added in M69 (still dev or beta), so the variance against the real number could be high). We use this number for roughly estimating those who are NOT affected by this removal.
Other less significant counters
V0CustomElementsCreateTypeExtensionElement
https://www.chromestatus.com/metrics/feature/timeline/popularity/1878 (~3.5%)
As M67 shipped type extension for Custom Elements V1, this number should decrease, and we will observe how this declines.
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=671907 (Shadow DOM V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=660759 (Custom Elements V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=766694 (HTML Imports)
Entry on the feature dashboard
https://www.chromestatus.com/features/4507242028072960 (Shadow DOM V0)
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)
Requesting approval to remove too?
Yes
Chris Harrelson
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Yoav Weiss
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smaug
> I'm concerned that the replacement of HTML imports will not be as performant. A couple performance characteristics that I really like about HTML
> imports are the browser's ability to progressively process them and its ability to tokenize them and preload their subresources.
>
> I haven't kept close tabs with the HTML modules effort so I don't know where it stands, but last time I looked, these characteristics would have been
> lost with the ES modules based proposal. It also seems like the HTML imports polyfill doesn't process them progressively
> So, it feels like we're removing a platform capability (or at least a convenience) without providing an edequate alternative.
>
It is a good thing to remove browser specific web exposed APIs.
-Olli
>
>
>
>
> On Tue, Aug 7, 2018 at 2:41 AM Chris Harrelson <chri...@chromium.org <mailto:chri...@chromium.org>> wrote:
>
> LGTM1
>
>
> *
>
> Primary eng (and PM) emails
>
> <mailto:yoi...@chromium.org>,
>
> Summary
>
> Remove Shadow DOM V0, Custom Elements V0, and HTML Imports at once in April, 2019 after deprecation period. All these pre-V1 era web
> components technologies except HTML Templates were not adopted by any other rendering engines. We discourage any usage of these APIs and
> encourage migrating to V1 APIs and ES modules.
>
>
> We are targeting M73 which will be on the stable channel in April 2019 to disable the features. Just in case people need more time for
>
>
> Here is the timeline.
>
>
>
> 2018Q2 (done)
>
> o
> Reach out Chrome internal users (e.g. WebUI)
>
> Analyze log data (UKM etc.) to identify non-polyfilled users
>
>
> 2018Q3
>
> o
> Start showing deprecation message on dev channel (M70)
>
> Proactively drive the usage down
>
>
> 2018Q4
>
> o
> Start showing deprecation message on stable channel (M70)
>
> Continue driving the usage down
>
>
> 2019Q1
>
> o
> Disable the feature in M73 (branch Jan. 2019)
>
>
> 2019Q2
>
> o
> Feature disabled in stable, start reverse origin trials for remaining users
>
>
> 2020Q1
>
> o
>
> Stop accepting origin trials
>
> *
>
> 2020Q2
>
> o
> Remove the code from the code base
>
>
> Motivation
>
>
> Shadow DOM V0, Custom Elements V0, and HTML Imports were launched in 2014, but they did not get adopted by other browser engines. Instead,
> Shadow DOM V1, Custom Elements V1, and ES modules are widely adopted by various browser engines today. Chrome has shipped Shadow DOM V1 /
> Custom Elements V1 in 2016 and ES modules in 2017.
>
>
> This is the second intent, the first one was to deprecate only Shadow DOM V0 in Nov. 2016
>
>
> Since then, we
>
>
> identified the most major users of Shadow DOM V0 and reached out to them (AdBlock Plus <https://issues.adblockplus.org/ticket/242>,
> AdBlock <https://help.getadblock.com/support/discussions/topics/6000044963>) , and helped them
> <https://bugs.chromium.org/p/chromium/issues/detail?id=632009>moving away from Shadow DOM V0, which resulted in significant usage drop
> corresponds to ~0.3% at that time).
>
> reached out Chrome internal users (e.g. Chrome WebUI used V0 APIs via Polymer V1) to migrate to V1 APIs (or Polymer V2+), tracked at
>
> *
>
> removed features of Shadow DOM V0 which are not available in V1 (/deep/ <https://bugs.chromium.org/p/chromium/issues/detail?id=489954>,
> multiple shadow roots <https://bugs.chromium.org/p/chromium/issues/detail?id=489947>) to facilitate web developers to migrate from Shadow
> DOM V0 to V1.
>
> *
>
> migrated Blink’s UA shadow implementation from V0 to V1 <https://bugs.chromium.org/p/chromium/issues/detail?id=787717>.
>
> *
>
> shipped type extension <https://bugs.chromium.org/p/chromium/issues/detail?id=648828>(aka “is=” attribute) for Custom Elements V1, for
>
> Opted in UKM for better analysis of which sites are using these APIs
>
> Analyzed httparchive data to identify list of sites that use the APIs
>
>
> Since then, we also found that in many real-world use cases, Shadow DOM V0, Custom Elements V0, HTML Imports were used together, and instead
> of getting each of them migrated respectively, getting all of them migrated to today’s standards at once, or at least use the polyfill would
> make it less troublesome, easier to migrate, rather than fighting with every edge case of combination of polyfill and native implementation.
>
>
> We found cases that some sites use browser sniffing to assume if it is “Chrome”, use native Custom Elements V0 and HTML Imports, and other
> sites once feature detect Shadow DOM V0, they assume Custom Elements V0 and HTML Imports are also available. The former can’t be helped, but
> the latter can be saved by one-off deprecation strategy.
>
>
> level of fidelity to native implementation, if we go the route of one-by-one deprecation, every site owner has to extensively test the site,
> while if we deprecate and remove at once, assuming the original site is designed to work for both Blink-based and non-Blink-based browsers
> using the polyfill, the probability that the site continues to work without any modification must be very high.
>
>
>
> Compatibility and Interoperability Risk
>
>
> No other browser engines support Shadow DOM V0, Custom Elements V0, and HTML Imports.
>
>
> Existing users of these APIs are mainly coming from Polymer V1 users (Shadow DOM V0, Custom Elements V0, and HTML Imports) and Polymer V2
> users (HTML Imports only, Shadow DOM and Custom Elements are V1). Fortunately for them, the impact should be minimal at the removal because
> these features are polyfilled and those pages should continue to work. Therefore even though their current usages via UMA look high, we can
> ignore the major portion of it (see below for details). We continue to figure out more exact usage of non-polyfilled sites that will break via
> various sources (UMA, UKM, httparchive, …).
>
>
>
> Note: even though Event.path was originally defined with Shadow DOM V0, and is superseded by Event.composedPath()
>
> Edge/IE: Not supported
>
> Firefox: Not supported
>
> Safari: Not supported
>
>
> Alternative implementation suggestion for web developers
>
>
> The most straightforward option is to migrate to Shadow DOM V1, Custom Elements V1, ES modules respectively at once. For Shadow DOM V1,
>
>
> If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as
> <https://github.com/webcomponents/webcomponentsjs/tree/v0>. There are other alternative polyfills for each, like AshleyScirra’s HTML Imports
> polyfill <https://github.com/AshleyScirra/html-imports-polyfill>.
>
> If you use Polymer V1 or V2, in most cases you do not have to take any action because the polyfill should kick in where these APIs are not
> available. If you would like to try if the polyfill works, you can pass --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to
> Note: at this moment Chrome’s devtools use Shadow DOM V0 and Custom Elements V0, if you pass the option above, you cannot open developer
>
> If you are an owner/developer of a site where any options above does not help, and cannot have time to do the work by the expected deadline
> getting a token to embed in a page to unlock the features. We use this for allowing to use deprecated features, aka “reverse origin trials”.
> How to apply for this will be sent out separately, when the removal date approaches (expecting in Jan 2019).
>
>
> If you encounter a site that you do not own, but is broken due to this deprecation, you can try passing
> --enable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome. This will work until we remove the code in 2020.
>
>
> Usage information from UseCounter
>
>
> Element.createShadowRoot() (representative for Shadow DOM V0 usage)
>
> https://www.chromestatus.com/metrics/feature/timeline/popularity/456(~1.7%)
>
> According to internal per-OS breakdown data, Android is the lowest (~0.85%) and other desktop OSes are all higher than 1.7%. It could mean
> that still some extensions use this. On httparchive mobile sites, we have only ~260 URLs out of Alexa 500,000 top mobile sites (~0.45%,
> because UMA takes page views into account, number % of top URLs must be smaller than UMA). By reaching out non-polyfilled sites we think we
> can reduce the pageview-based number of non-polyfilled sites to below 0.1% within this deprecation period.
>
>
> Document.registerElement() (representative for Custom Elements V0 usage)
>
> https://www.chromestatus.com/metrics/feature/timeline/popularity/457(~5.0%)
>
> We are aware that this number is high, however, this includes YouTube desktop usage. We have been talking with YouTube team. From internal UMA
> per-OS breakdown, Android is ~3.8% (and other desktop OSes are above 5%). We have ~4000 URLs in httparchive for mobile sites (~0.8%), and will
> pick up non-polyfilled sites and reach them out. Even for non-polyfilled sites, unless they run Blink-based browser only sites, we assume most
> of them feature-detect with some fallback, therefore problematic sites should be very few (to be closely analyzed, though).
>
>
> HTML Imports (<link rel=”import”>)
>
> https://www.chromestatus.com/metrics/feature/timeline/popularity/455(~2.0%)
>
> We are aware that this number is high, however, this includes YouTube desktop usage. From internal UMA per-OS breakdown, Android is ~0.13%
> (and other desktop OSs are above 2%). Once YouTube desktop move out of HTML Imports, desktop numbers should become closer to Android’s. From
> httparchive mobile sites, ~280 URLs (out of 500,000 - ~0.6%) pmeenan@ already looked at these list
>
>
> Polymer V1 (detected by “dom-module” registration via document.registerElement)
>
> https://www.chromestatus.com/metrics/feature/timeline/popularity/2466(~1.9%)
>
> This includes desktop YouTube usage (Note: this counter is added in M69 (still dev or beta), so the variance against the real number could be
> high). We use this number for roughly estimating those who are NOT affected by this removal.
>
>
>
> Other less significant counters
>
>
> V0CustomElementsCreateTypeExtensionElement
>
> https://www.chromestatus.com/metrics/feature/timeline/popularity/1878(~3.5%)
>
> As M67 shipped type extension for Custom Elements V1, this number should decrease, and we will observe how this declines.
>
>
> Tracking bug
>
> https://bugs.chromium.org/p/chromium/issues/detail?id=671907(Shadow DOM V0)
>
> https://bugs.chromium.org/p/chromium/issues/detail?id=660759(Custom Elements V0)
>
>
> Entry on the feature dashboard
>
> https://www.chromestatus.com/features/4507242028072960(Shadow DOM V0)
>
> https://www.chromestatus.com/feature/4642138092470272(Custom Elements V0)
>
>
> Requesting approval to remove too?
>
> Yes
>
>
> --
> Hayato
> --
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nsi...@nuxeo.com
There isn't any comparable alternative yet apart from ES Modules which require generating HTML and CSS with JS. HTML modules are the most similar proposal but very far from even a first implementation. IMHO it would make sense to delay deprecation of HTML imports until we have HTML modules or a way to leverage ES Modules to load HTML.
PhistucK
I can't help but feel that the deprecation of HTML imports is being rushed and should be decoupled from the deprecation of CE and Shadow DOM V0. Agree it's not good to keep non standard APIs but HTML imports are being used with CE and Shadow DOM V1 in Polymer 2 for instance which was released just a year ago!
There isn't any comparable alternative yet apart from ES Modules which require generating HTML and CSS with JS. HTML modules are the most similar proposal but very far from even a first implementation. IMHO it would make sense to delay deprecation of HTML imports until we have HTML modules or a way to leverage ES Modules to load HTML.
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TAMURA, Kent
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Software Engineer, Google
Nelson Silva
We currently rely heavily on HTML imports to allow *declarative* building of custom elements for enterprise content management applications. These come with long term support.
We have migrated away from the V0 APIs and are planning migrating from HTML imports but there is no direct replacement at this time, not one that allows us to stick to HTML without some form of building/bundling process.
Today we rely on the polyfill for other browsers but at least we have a nice development experience with Chrome which shows the imports as HTML documents and not as nasty data urls.
I am well aware this is not the time or place to discuss the adoption of HTML imports as a standard since that "battle" has been lost a long time ago but I still have hopes for a real alternative that allows us to keep HTML for it's declarative nature and would hope for HTML imports to be there, at least in Chrome, until we have a comparable alternative.
Hayato Ito
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Philip Jägenstedt
A very comprehensive plan and research into existing usage, thank you!
Working with ad blocking extensions to drive down usage from 14% to 2%
is particularly impressive!
The rationale for linking these deprecations makes perfect sense to
me, it will allow web developers to react to the change once.
Yoav, do you still have concerns with removing HTML imports? If so
please do not let the 3xLGTM stop the discussion on this thread.
Philip Jägenstedt
Domenic Denicola
> We're still concerned that the replacement will be less performant than HTML imports,
> and would like to understand if there's any path forward. mailto:d...@domenic.me, what are your current views on "HTML modules", and what it would take to ship something with multi-vendor support?
HTML modules make a lot of sense to me in theory, as they allow the standards, implementer, and web developer community to converge on a single module system and optimize the heck out of it. (See previous threads for updates on the loading team's ongoing efforts in that area for the JS module system).
Hayato is right that no browsers seem to object to it, and that it mostly just needs someone to do the legwork. The discussion is at https://github.com/w3c/webcomponents/issues/645, but nobody seems to be devoting full-time effort to it. I think last we saw putting together a concrete proposal was part of the Polymer OKRs, with mentoring from the DOM team, but I haven't seen any progress for a while.
Hayato Ito
From: Philip Jägenstedt <foo...@chromium.org>
> We're still concerned that the replacement will be less performant than HTML imports,
My understanding is that many of the theoretical performance benefits of HTML imports were not, in the end, implemented; in practice to get acceptable performance with them sites had to use tooling like Vulcanize to inline their contents into the main page. See https://www.polymer-project.org/1.0/docs/tools/optimize-for-production for example. Hayato or the rest of the DOM team can weigh in further.
Yoav Weiss
On Wed, Aug 15, 2018 at 1:25 AM Domenic Denicola <d...@domenic.me> wrote:From: Philip Jägenstedt <foo...@chromium.org>
> We're still concerned that the replacement will be less performant than HTML imports,
My understanding is that many of the theoretical performance benefits of HTML imports were not, in the end, implemented; in practice to get acceptable performance with them sites had to use tooling like Vulcanize to inline their contents into the main page. See https://www.polymer-project.org/1.0/docs/tools/optimize-for-production for example. Hayato or the rest of the DOM team can weigh in further.
Yeah, in practice, I think most sites are using Vulcanize at this point.Polymer has already switched to use ES Modules, and I've not heard any significant performance regression on this switch, compared to HTML Imports.
We know that ES Modules couldn't be a replacement of HTML Imports because they solve a different problem, however, from the performance perspective, ES Modules shouldn't be less performant than HTML imports.
ES Modules' performance is getting better and better, I think.In addition to that, as Olli@ pointed out in this thread, other browsers never get performance benefits from HTML Imports.Polymer team would have more insights on the performance.--Hayato
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Yoav Weiss
Usage information from UseCounter
...
HTML Imports (<link rel=”import”>)
https://www.chromestatus.com/metrics/feature/timeline/popularity/455 (~2.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. From internal UMA per-OS breakdown, Android is ~0.13% (and other desktop OSs are above 2%). Once YouTube desktop move out of HTML Imports, desktop numbers should become closer to Android’s. From httparchive mobile sites, ~280 URLs (out of 500,000 - ~0.6%) pmeenan@ already looked at these list and 175 out of 277 are identified using web components polyfill. So ~100 sites out of 500,000 sites will be affected by this, which is ~0.02% of sites.
Hayato Ito
On Wed, Aug 15, 2018 at 3:17 PM Hayato Ito <hay...@chromium.org> wrote:On Wed, Aug 15, 2018 at 1:25 AM Domenic Denicola <d...@domenic.me> wrote:From: Philip Jägenstedt <foo...@chromium.org>
> We're still concerned that the replacement will be less performant than HTML imports,
My understanding is that many of the theoretical performance benefits of HTML imports were not, in the end, implemented; in practice to get acceptable performance with them sites had to use tooling like Vulcanize to inline their contents into the main page. See https://www.polymer-project.org/1.0/docs/tools/optimize-for-production for example. Hayato or the rest of the DOM team can weigh in further.
Yeah, in practice, I think most sites are using Vulcanize at this point.Polymer has already switched to use ES Modules, and I've not heard any significant performance regression on this switch, compared to HTML Imports.Interesting. Was the existing implementation not optimized to go through preloadScanning and progressive DOM building? Or are the payloads typically used too small for it to make a difference?
We know that ES Modules couldn't be a replacement of HTML Imports because they solve a different problem, however, from the performance perspective, ES Modules shouldn't be less performant than HTML imports.Can the HTML modules model enable progressive tokenization and DOM building?
----ES Modules' performance is getting better and better, I think.In addition to that, as Olli@ pointed out in this thread, other browsers never get performance benefits from HTML Imports.Polymer team would have more insights on the performance.--Hayato
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Yoav Weiss
On Thu, Aug 16, 2018 at 8:17 PM Yoav Weiss <yo...@yoav.ws> wrote:On Wed, Aug 15, 2018 at 3:17 PM Hayato Ito <hay...@chromium.org> wrote:On Wed, Aug 15, 2018 at 1:25 AM Domenic Denicola <d...@domenic.me> wrote:From: Philip Jägenstedt <foo...@chromium.org>
> We're still concerned that the replacement will be less performant than HTML imports,
My understanding is that many of the theoretical performance benefits of HTML imports were not, in the end, implemented; in practice to get acceptable performance with them sites had to use tooling like Vulcanize to inline their contents into the main page. See https://www.polymer-project.org/1.0/docs/tools/optimize-for-production for example. Hayato or the rest of the DOM team can weigh in further.
Yeah, in practice, I think most sites are using Vulcanize at this point.Polymer has already switched to use ES Modules, and I've not heard any significant performance regression on this switch, compared to HTML Imports.Interesting. Was the existing implementation not optimized to go through preloadScanning and progressive DOM building? Or are the payloads typically used too small for it to make a difference?I don't think any implementation of ES Modules are doing progressive DOM building. I think you can get more insights from ES Modules owners.
We know that ES Modules couldn't be a replacement of HTML Imports because they solve a different problem, however, from the performance perspective, ES Modules shouldn't be less performant than HTML imports.Can the HTML modules model enable progressive tokenization and DOM building?That is basically up-to UA. I don't see any reason Blink can't do that for HTML Modules.I guess the reason you asked these questions is to let us know that HTML Modules would be much better than ES Modules, regarding loading HTML and DOM building. Yup, that is the reason that we would like to move HTML Modules forward.
Hayato Ito
On Thu, Aug 16, 2018 at 2:26 PM Hayato Ito <hay...@chromium.org> wrote:On Thu, Aug 16, 2018 at 8:17 PM Yoav Weiss <yo...@yoav.ws> wrote:On Wed, Aug 15, 2018 at 3:17 PM Hayato Ito <hay...@chromium.org> wrote:On Wed, Aug 15, 2018 at 1:25 AM Domenic Denicola <d...@domenic.me> wrote:From: Philip Jägenstedt <foo...@chromium.org>
> We're still concerned that the replacement will be less performant than HTML imports,
My understanding is that many of the theoretical performance benefits of HTML imports were not, in the end, implemented; in practice to get acceptable performance with them sites had to use tooling like Vulcanize to inline their contents into the main page. See https://www.polymer-project.org/1.0/docs/tools/optimize-for-production for example. Hayato or the rest of the DOM team can weigh in further.
Yeah, in practice, I think most sites are using Vulcanize at this point.Polymer has already switched to use ES Modules, and I've not heard any significant performance regression on this switch, compared to HTML Imports.Interesting. Was the existing implementation not optimized to go through preloadScanning and progressive DOM building? Or are the payloads typically used too small for it to make a difference?I don't think any implementation of ES Modules are doing progressive DOM building. I think you can get more insights from ES Modules owners.Apologies for not being clearer. By "existing implementation" I was referring to the current HTML imports implementation.We know that ES Modules couldn't be a replacement of HTML Imports because they solve a different problem, however, from the performance perspective, ES Modules shouldn't be less performant than HTML imports.Can the HTML modules model enable progressive tokenization and DOM building?That is basically up-to UA. I don't see any reason Blink can't do that for HTML Modules.I guess the reason you asked these questions is to let us know that HTML Modules would be much better than ES Modules, regarding loading HTML and DOM building. Yup, that is the reason that we would like to move HTML Modules forward.I was asking that because I wanted to know the answer :)I wasn't sure if the reliance on ES modules as infrastructure would make it more difficult to process the HTML content progressively.Glad to see you don't foresee any difficulties there, and glad to hear HTML modules is something the team continues to pursue.
----ES Modules' performance is getting better and better, I think.In addition to that, as Olli@ pointed out in this thread, other browsers never get performance benefits from HTML Imports.Polymer team would have more insights on the performance.--Hayato
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Yoav Weiss
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Philip Jägenstedt
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PhistucK
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Hayato Ito
Pavel Feldman
I can add them to the thread where we discussed it with the team, Rick and myself. We had a nice plan for it back then, but instead of executing on that plan we are seeing another attempt to deprecate.
Anne van Kesteren
> My understanding is that Safari's Shadow DOM v1 is different from Blink's. I.e. DevTools, AdBlock, YouTube, Polymer would work in Chrome, but not in Safari.
not the standardized APIs? Other than customized built-in elements I'm
not aware of any outstanding disagreements on the standardized API.
Pointers appreciated.
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Pavel Feldman
Rick Byers
Yoichi Osato
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Hayato Ito
Pavel Feldman
The section is what you might want to check. This section has been there for a long time.That is *never* standardized.
Hayato Ito
Hayato Ito
On Mon, Aug 27, 2018 at 7:40 PM Hayato Ito <hay...@chromium.org> wrote:The section is what you might want to check. This section has been there for a long time.That is *never* standardized.The spec says "Implementation should do their best to do what's best for them.". What do you mean "that is never standardized"? I think we should standardize it though?
I understand how we are interested in shipping v1 incrementally, but the spec has gaps, sometimes large and with no shared visions among the vendors. We are forcing v0 adopters to migrate to v1 today. Does this mean that we will be pushing them to v2 again once selection, aria references and other areas are aligned and implemented?My only goal was to raise the awareness among the OWNERS, which I believe I achieved. I trust them to make the right call.
Hayato Ito
j.j.
Entry on the feature dashboard
https://www.chromestatus.com/features/4507242028072960 (Shadow DOM V0)
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)
Yoichi Osato
Hayato Ito
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dpa...@google.com
On Thursday, August 9, 2018 at 2:58:03 PM UTC-7, PhistucK wrote:
> but HTML imports are being used with CE and Shadow DOM V1 in Polymer 2 for instance which was released just a year ago!That was probably a mistake on their part, because all of the other vendors indicated opposition to HTML imports for years, if I remember correctly.However, it is only an optimization, if I am not mistaken and it will work even without HTML import support, so it does not really matter much.
☆PhistucKOn Fri, Aug 10, 2018 at 12:35 AM <nsi...@nuxeo.com> wrote:I can't help but feel that the deprecation of HTML imports is being rushed and should be decoupled from the deprecation of CE and Shadow DOM V0. Agree it's not good to keep non standard APIs but HTML imports are being used with CE and Shadow DOM V1 in Polymer 2 for instance which was released just a year ago!
There isn't any comparable alternative yet apart from ES Modules which require generating HTML and CSS with JS. HTML modules are the most similar proposal but very far from even a first implementation. IMHO it would make sense to delay deprecation of HTML imports until we have HTML modules or a way to leverage ES Modules to load HTML.
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Hayato Ito
Why use ES modules when google style guide for Javascript (https://google.github.io/styleguide/jsguide.html) at 3.3 4 says not to use ES modules?
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Yoichi Osato
Hello, we have been developing lots of webapps with WebComponents since 2016. We create link rel="imports" on the fly and no polyfill helps in that case. Our app defines WebAudio plugins that can be dynamically imported on demand in host applications.We understand clearly that html imports will not be adopted. Please, before discarding them, can the WebComponent WG publish a guide for helping us migrating to something that will be supported ? How can we replace our imports by ES6 modules? I just can't see any solution except bundling everything in JS using Webpack + plugins... Is that the solution you suggest?Michel
Le lundi 30 juillet 2018 09:35:19 UTC+2, Hayato Ito a écrit :
Primary eng (and PM) emails
Summary
Remove Shadow DOM V0, Custom Elements V0, and HTML Imports at once in April, 2019 after deprecation period. All these pre-V1 era web components technologies except HTML Templates were not adopted by any other rendering engines. We discourage any usage of these APIs and encourage migrating to V1 APIs and ES modules.
We are targeting M73 which will be on the stable channel in April 2019 to disable the features. Just in case people need more time for migration, we plan to provide an option of using origin trials to keep using the APIs, see below for details.
Here is the timeline.
2018Q2 (done)
Reach out Chrome internal users (e.g. WebUI)
Analyze log data (UKM etc.) to identify non-polyfilled users
2018Q3
Start showing deprecation message on dev channel (M70)
Proactively drive the usage down
2018Q4
Start showing deprecation message on stable channel (M70)
Continue driving the usage down
2019Q1
Disable the feature in M73 (branch Jan. 2019)
2019Q2
Feature disabled in stable, start reverse origin trials for remaining users
2020Q1
Stop accepting origin trials
2020Q2
Remove the code from the code base
Motivation
Shadow DOM V0, Custom Elements V0, and HTML Imports were launched in 2014, but they did not get adopted by other browser engines. Instead, Shadow DOM V1, Custom Elements V1, and ES modules are widely adopted by various browser engines today. Chrome has shipped Shadow DOM V1 / Custom Elements V1 in 2016 and ES modules in 2017.
This is the second intent, the first one was to deprecate only Shadow DOM V0 in Nov. 2016 after Shadow DOM V1 shipped. We withheld deprecating mostly because we had not analyzed the usage at that time.
Since then, we
identified the most major users of Shadow DOM V0 and reached out to them (AdBlock Plus, AdBlock) , and helped them moving away from Shadow DOM V0, which resulted in significant usage drop (14% to 2% - considering the usage was 2.2% at the previous intent post with a different measurement method than today, current 2% corresponds to ~0.3% at that time).
reached out Chrome internal users (e.g. Chrome WebUI used V0 APIs via Polymer V1) to migrate to V1 APIs (or Polymer V2+), tracked at crbug.com/806159. Half of them are done, and the rest have plan to meet the timeline.
removed features of Shadow DOM V0 which are not available in V1 (/deep/, multiple shadow roots) to facilitate web developers to migrate from Shadow DOM V0 to V1.
migrated Blink’s UA shadow implementation from V0 to V1.
shipped type extension (aka “is=” attribute) for Custom Elements V1, for Custom Element V0 users to migrate to V1
Opted in UKM for better analysis of which sites are using these APIs
Analyzed httparchive data to identify list of sites that use the APIs
Since then, we also found that in many real-world use cases, Shadow DOM V0, Custom Elements V0, HTML Imports were used together, and instead of getting each of them migrated respectively, getting all of them migrated to today’s standards at once, or at least use the polyfill would make it less troublesome, easier to migrate, rather than fighting with every edge case of combination of polyfill and native implementation.
We found cases that some sites use browser sniffing to assume if it is “Chrome”, use native Custom Elements V0 and HTML Imports, and other sites once feature detect Shadow DOM V0, they assume Custom Elements V0 and HTML Imports are also available. The former can’t be helped, but the latter can be saved by one-off deprecation strategy.
Note: the polyfill (webcomponentsjs) is designed to feature-detect and polyfill any combination of Shadow DOM V0, Custom Elements V0, HTML Imports. Having said that, each has its own implementation limitation and different level of fidelity to native implementation, if we go the route of one-by-one deprecation, every site owner has to extensively test the site, while if we deprecate and remove at once, assuming the original site is designed to work for both Blink-based and non-Blink-based browsers using the polyfill, the probability that the site continues to work without any modification must be very high.
Compatibility and Interoperability Risk
No other browser engines support Shadow DOM V0, Custom Elements V0, and HTML Imports.
Existing users of these APIs are mainly coming from Polymer V1 users (Shadow DOM V0, Custom Elements V0, and HTML Imports) and Polymer V2 users (HTML Imports only, Shadow DOM and Custom Elements are V1). Fortunately for them, the impact should be minimal at the removal because these features are polyfilled and those pages should continue to work. Therefore even though their current usages via UMA look high, we can ignore the major portion of it (see below for details). We continue to figure out more exact usage of non-polyfilled sites that will break via various sources (UMA, UKM, httparchive, …).
Most of Chrome internal usage (such as Chrome Web UI) has migration plans and it is tracked at crbug.com/806159.
Note: even though Event.path was originally defined with Shadow DOM V0, and is superseded by Event.composedPath() in the V1 spec, Event.path can work without Shadow DOM V0 and will be deprecated separately.
Edge/IE: Not supported
Firefox: Not supported
Safari: Not supported
Alternative implementation suggestion for web developers
The most straightforward option is to migrate to Shadow DOM V1, Custom Elements V1, ES modules respectively at once. For Shadow DOM V1, there’s a document to compare V0 and V1 APIs. As this is not a simple replacement of APIs, it may be time consuming.
If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as “webcomponentsjs”. Specifically for polyfilling V0 APIs, you can use its v0 branch. There are other alternative polyfills for each, like AshleyScirra’s HTML Imports polyfill.
If you use Polymer V1 or V2, in most cases you do not have to take any action because the polyfill should kick in where these APIs are not available. If you would like to try if the polyfill works, you can pass --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome (see howto document for passing command line parameter). To be more future proof, it is a good idea to migrate to a newer version of Polymer, see their document for upgrading to 3.0 and 2.0.
Note: at this moment Chrome’s devtools use Shadow DOM V0 and Custom Elements V0, if you pass the option above, you cannot open developer tools. In that case you can use remote debugging.
If you are an owner/developer of a site where any options above does not help, and cannot have time to do the work by the expected deadline (April 2019), we plan to offer an option to use origin trials to opt-in for the site to enable deprecated features for up to 1 year. Origin Trials are a mechanism that a site owner can apply for using Chrome’s experimental features, by getting a token to embed in a page to unlock the features. We use this for allowing to use deprecated features, aka “reverse origin trials”. How to apply for this will be sent out separately, when the removal date approaches (expecting in Jan 2019).
If you encounter a site that you do not own, but is broken due to this deprecation, you can try passing --enable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome. This will work until we remove the code in 2020.
Usage information from UseCounter
Element.createShadowRoot() (representative for Shadow DOM V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/456 (~1.7%)
According to internal per-OS breakdown data, Android is the lowest (~0.85%) and other desktop OSes are all higher than 1.7%. It could mean that still some extensions use this. On httparchive mobile sites, we have only ~260 URLs out of Alexa 500,000 top mobile sites (~0.45%, because UMA takes page views into account, number % of top URLs must be smaller than UMA). By reaching out non-polyfilled sites we think we can reduce the pageview-based number of non-polyfilled sites to below 0.1% within this deprecation period.
Document.registerElement() (representative for Custom Elements V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/457 (~5.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. We have been talking with YouTube team. From internal UMA per-OS breakdown, Android is ~3.8% (and other desktop OSes are above 5%). We have ~4000 URLs in httparchive for mobile sites (~0.8%), and will pick up non-polyfilled sites and reach them out. Even for non-polyfilled sites, unless they run Blink-based browser only sites, we assume most of them feature-detect with some fallback, therefore problematic sites should be very few (to be closely analyzed, though).
HTML Imports (<link rel=”import”>)
https://www.chromestatus.com/metrics/feature/timeline/popularity/455 (~2.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. From internal UMA per-OS breakdown, Android is ~0.13% (and other desktop OSs are above 2%). Once YouTube desktop move out of HTML Imports, desktop numbers should become closer to Android’s. From httparchive mobile sites, ~280 URLs (out of 500,000 - ~0.6%) pmeenan@ already looked at these list and 175 out of 277 are identified using web components polyfill. So ~100 sites out of 500,000 sites will be affected by this, which is ~0.02% of sites.
Polymer V1 (detected by “dom-module” registration via document.registerElement)
https://www.chromestatus.com/metrics/feature/timeline/popularity/2466 (~1.9%)
This includes desktop YouTube usage (Note: this counter is added in M69 (still dev or beta), so the variance against the real number could be high). We use this number for roughly estimating those who are NOT affected by this removal.
Other less significant counters
V0CustomElementsCreateTypeExtensionElement
https://www.chromestatus.com/metrics/feature/timeline/popularity/1878 (~3.5%)
As M67 shipped type extension for Custom Elements V1, this number should decrease, and we will observe how this declines.
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=671907 (Shadow DOM V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=660759 (Custom Elements V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=766694 (HTML Imports)
Entry on the feature dashboard
https://www.chromestatus.com/features/4507242028072960 (Shadow DOM V0)
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)
Requesting approval to remove too?
Yes
--Hayato
micb...@gmail.com
luk...@google.com
if you need to know in the browser process whether a feature shouldbe enabled, then you will have to either have the renderer inform it at runtime,or else just assume that it's always enabled, and gate access to the featurefrom the renderer
The most straightforward option is to migrate to Shadow DOM V1, Custom Elements V1, ES modules respectively at once. For Shadow DOM V1, there’s a document<span style="font-s
Yoichi Osato
nae...@gmail.com
On Monday, July 30, 2018 at 3:35:19 AM UTC-4, Hayato Ito wrote:
Summary
Remove Shadow DOM V0, Custom Elements V0, and HTML Imports at once in April, 2019 after deprecation period. All these pre-V1 era web components technologies except HTML Templates were not adopted by any other rendering engines. We discourage any usage of these APIs and encourage migrating to V1 APIs and ES modules.
Yoichi Osato
Yoichi Osato
Thanks everyone for reviewing this and preparation work.
Since some Chrome internal components/tests using the APIs didn't finish migration work and some new ones were found, I decided to postpone API removal to M74.
Here is updated timeline:
2019 Q2(M74)
Disable the APIs.
Start reverse origin trials since M74 beta launches.
2020 Q2(M81)
Stop accepting origin trials (would be cut earlier if usage is enough low).
Remove the code and no one can use the APIs anyway.
Tracking bugs for the internal migration (I hope I’m grabbing all blockers):
DevTools: crbug.com/685385
WebUI: crbug.com/738611
PDF: crbug.com/924031
Browser tests: crbug.com/924034
External usage: Chrome status (as 2019 Jan current). Diff is from 2018 July as the first intent mail.
Shadow DOM V0: 1.5% (-0.2%)
Custom Elements V0: 4.5% (-0.5%)
HTML Imports: 1.8% (-0.2%)
The usage is still high but I didn’t find any big sites using the APIs except YouTube. I got to feel there was a metrics magic and the stat didn’t reflect actual usage,,,
michel buffa
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rictic
jeffrey...@gmail.com
Can somebody tell me how to test if our components keep working with version 73?
Op maandag 30 juli 2018 09:35:19 UTC+2 schreef Hayato Ito:
Summary
Remove Shadow DOM V0, Custom Elements V0, and HTML Imports at once in April, 2019 after deprecation period. All these pre-V1 era web components technologies except HTML Templates were not adopted by any other rendering engines. We discourage any usage of these APIs and encourage migrating to V1 APIs and ES modules.
Peter Burns
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Jeremy Roman
Hi,We are using Polymer 2 components on our site, and I'd like to test the deprecation of HTMLImports in Chrome 73.The documentation specifies using the following Chrome flags: --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImportsBut when I use these flags Chrome (version 72) starts with the message "You are usin an unsupported command-line flag: --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports. Stability and security will suffer."
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jeffrey...@gmail.com
Op woensdag 30 januari 2019 21:20:06 UTC+1 schreef rictic:
If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as “webcomponentsjs”. Specifically for polyfilling V0 APIs, you can use its v0 branch. There are other alternative polyfills for each, like AshleyScirra’s <span style="font-size:9.5pt;font-family:Arial;color:rgb(17,85,204);background-color:transparent;font-weight:400;font-style:normal;font-variant:normal;text-
jeffrey...@gmail.com
and without the blink features
Op woensdag 30 januari 2019 22:26:41 UTC+1 schreef Jeremy Roman:
If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as “webcomponentsjs”. Specifically for polyfilling V0 APIs, you can use its v0 branch<span style="font-size:9.5pt;font-family:Arial;color:rgb(34,34,34);background-color:transparent;font-weight:400;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:
thomasmu...@yahoo.com
PhistucK
Hi, does this mean PolyGerrit will stop working in chrome? It uses Polymer 1.x and also i see the deprecated warning in the browser console log.
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fau...@thexs.ca
Note: even though Event.path was originally defined with Shadow DOM V0, and is superseded by <a href="https://dom.spec.whatwg.org/#dom-event-composedpath" style="text-decoration:none" rel="nofollow" target="_blank" onmousedown="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fdom.spec.whatwg.org%2F%23dom-event-composedpath\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFHN80EAVP7Ce0PZehZaQiI39Jg7A';return true;" onclick="this.href='https://www.google.com/url?q\x3dhttps%3A%2F%2Fdom.spec.whatwg.org%2F%23dom-event-composedpath\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFHN80EAVP7Ce0PZeh
Mike West
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Yoichi Osato
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Hayato Ito
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Yoichi Osato
Nelson Silva
Most of Chrome internal usage (such as Chrome Web UI) has migration plans and it is tracked at <span style
Thomas Steiner
Philip Jägenstedt
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Philip Jägenstedt
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Philip Jägenstedt
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Yoichi Osato
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michel buffa
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michel buffa
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<span style="font-size:9.5pt;font-family:Arial;color:rgb(34,34,34);background-color:transpa
Yoichi Osato
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cheruk...@gmail.com
2019年3月7日(木) 9:19 <cheruk...@gmail.com>:
reached out Chrome internal users (e.g. Chrome WebUI used V0 APIs via Polymer V1) to migrate to V1 APIs (or Polymer V2+), tracked at <a href="https://crbug.com/806159" style="text-decoration:none" rel="
tigerh...@gmail.com
reached out Chrome internal users (e.g. Chrome WebUI used V0 APIs via Polymer V1) to migrate to V1 APIs (or Polymer V2+), tracked at crbug.com/806159. Half of them are done, and the rest have plan to meet the timeline.
removed features of Shadow DOM V0 which are not available in V1 (/deep/, multiple shadow roots) to facilitate web developers to migrate from Shadow DOM V0 to V1.
migrated Blink’s UA shadow implementation from V0 to V1.
shipped type extension (aka “is=” attribute) for Custom Elements V1, for Custom Element V0 users to migrate to V1
Opted in UKM for better analysis of which sites are using these APIs
Analyzed httparchive data to identify list of sites that use the APIs
Since then, we also found that in many real-world use cases, Shadow DOM V0, Custom Elements V0, HTML Imports were used together, and instead of getting each of them migrated respectively, getting all of them migrated to today’s standards at once, or at least use the polyfill would make it less troublesome, easier to migrate, rather than fighting with every edge case of combination of polyfill and native implementation.
We found cases that some sites use browser sniffing to assume if it is “Chrome”, use native Custom Elements V0 and HTML Imports, and other sites once feature detect Shadow DOM V0, they assume Custom Elements V0 and HTML Imports are also available. The former can’t be helped, but the latter can be saved by one-off deprecation strategy.
Note: the polyfill (webcomponentsjs) is designed to feature-detect and polyfill any combination of Shadow DOM V0, Custom Elements V0, HTML Imports. Having said that, each has its own implementation limitation and different level of fidelity to native implementation, if we go the route of one-by-one deprecation, every site owner has to extensively test the site, while if we deprecate and remove at once, assuming the original site is designed to work for both Blink-based and non-Blink-based browsers using the polyfill, the probability that the site continues to work without any modification must be very high.
Compatibility and Interoperability Risk
No other browser engines support Shadow DOM V0, Custom Elements V0, and HTML Imports.
Existing users of these APIs are mainly coming from Polymer V1 users (Shadow DOM V0, Custom Elements V0, and HTML Imports) and Polymer V2 users (HTML Imports only, Shadow DOM and Custom Elements are V1). Fortunately for them, the impact should be minimal at the removal because these features are polyfilled and those pages should continue to work. Therefore even though their current usages via UMA look high, we can ignore the major portion of it (see below for details). We continue to figure out more exact usage of non-polyfilled sites that will break via various sources (UMA, UKM, httparchive, …).
Most of Chrome internal usage (such as Chrome Web UI) has migration plans and it is tracked at crbug.com/806159.
Note: even though Event.path was originally defined with Shadow DOM V0, and is superseded by Event.composedPath() in the V1 spec, Event.path can work without Shadow DOM V0 and will be deprecated separately.
Edge/IE: Not supported
Firefox: Not supported
Safari: Not supported
Alternative implementation suggestion for web developers
The most straightforward option is to migrate to Shadow DOM V1, Custom Elements V1, ES modules respectively at once. For Shadow DOM V1, there’s a document to compare V0 and V1 APIs. As this is not a simple replacement of APIs, it may be time consuming.
If you use the features without Polymer, one option is to use a polyfill. The polyfill bundled with Polymer is separately available as “webcomponentsjs”. Specifically for polyfilling V0 APIs, you can use its v0 branch. There are other alternative polyfills for each, like AshleyScirra’s HTML Imports polyfill.
If you use Polymer V1 or V2, in most cases you do not have to take any action because the polyfill should kick in where these APIs are not available. If you would like to try if the polyfill works, you can pass --disable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome (see howto document for passing command line parameter). To be more future proof, it is a good idea to migrate to a newer version of Polymer, see their document for upgrading to 3.0 and 2.0.
Note: at this moment Chrome’s devtools use Shadow DOM V0 and Custom Elements V0, if you pass the option above, you cannot open developer tools. In that case you can use remote debugging.
If you are an owner/developer of a site where any options above does not help, and cannot have time to do the work by the expected deadline (April 2019), we plan to offer an option to use origin trials to opt-in for the site to enable deprecated features for up to 1 year. Origin Trials are a mechanism that a site owner can apply for using Chrome’s experimental features, by getting a token to embed in a page to unlock the features. We use this for allowing to use deprecated features, aka “reverse origin trials”. How to apply for this will be sent out separately, when the removal date approaches (expecting in Jan 2019).
If you encounter a site that you do not own, but is broken due to this deprecation, you can try passing --enable-blink-features=ShadowDOMV0,CustomElementsV0,HTMLImports to Chrome. This will work until we remove the code in 2020.
Usage information from UseCounter
Element.createShadowRoot() (representative for Shadow DOM V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/456 (~1.7%)
According to internal per-OS breakdown data, Android is the lowest (~0.85%) and other desktop OSes are all higher than 1.7%. It could mean that still some extensions use this. On httparchive mobile sites, we have only ~260 URLs out of Alexa 500,000 top mobile sites (~0.45%, because UMA takes page views into account, number % of top URLs must be smaller than UMA). By reaching out non-polyfilled sites we think we can reduce the pageview-based number of non-polyfilled sites to below 0.1% within this deprecation period.
Document.registerElement() (representative for Custom Elements V0 usage)
https://www.chromestatus.com/metrics/feature/timeline/popularity/457 (~5.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. We have been talking with YouTube team. From internal UMA per-OS breakdown, Android is ~3.8% (and other desktop OSes are above 5%). We have ~4000 URLs in httparchive for mobile sites (~0.8%), and will pick up non-polyfilled sites and reach them out. Even for non-polyfilled sites, unless they run Blink-based browser only sites, we assume most of them feature-detect with some fallback, therefore problematic sites should be very few (to be closely analyzed, though).
HTML Imports (<link rel=”import”>)
https://www.chromestatus.com/metrics/feature/timeline/popularity/455 (~2.0%)
We are aware that this number is high, however, this includes YouTube desktop usage. From internal UMA per-OS breakdown, Android is ~0.13% (and other desktop OSs are above 2%). Once YouTube desktop move out of HTML Imports, desktop numbers should become closer to Android’s. From httparchive mobile sites, ~280 URLs (out of 500,000 - ~0.6%) pmeenan@ already looked at these list and 175 out of 277 are identified using web components polyfill. So ~100 sites out of 500,000 sites will be affected by this, which is ~0.02% of sites.
Polymer V1 (detected by “dom-module” registration via document.registerElement)
https://www.chromestatus.com/metrics/feature/timeline/popularity/2466 (~1.9%)
This includes desktop YouTube usage (Note: this counter is added in M69 (still dev or beta), so the variance against the real number could be high). We use this number for roughly estimating those who are NOT affected by this removal.
Other less significant counters
V0CustomElementsCreateTypeExtensionElement
https://www.chromestatus.com/metrics/feature/timeline/popularity/1878 (~3.5%)
As M67 shipped type extension for Custom Elements V1, this number should decrease, and we will observe how this declines.
Tracking bug
https://bugs.chromium.org/p/chromium/issues/detail?id=671907 (Shadow DOM V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=660759 (Custom Elements V0)
https://bugs.chromium.org/p/chromium/issues/detail?id=766694 (HTML Imports)
Entry on the feature dashboard
https://www.chromestatus.com/features/4507242028072960 (Shadow DOM V0)
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)
Requesting approval to remove too?
Yes
--Hayato
j.j.
Am Dienstag, 5. März 2019 07:02:10 UTC+1 schrieb Yoichi Osato:
Updates: postpone API removal to M75.
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)
Yoichi Osato
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valeria...@elca.ch
- crbug.com/806159 is marked for M76 and as blocking the API removal. Will the concerned systems have a specific access to the API?
- The API removal doesn't seem present on Canary. Do you plan to apply the change to it soon?
- It doesn't seem compatible with what was suggested earlier in this thread
I would suggest that 2-3 milestones after internal Google projects and properties all have been updated as the earliest milestone for removal.
- Do you plan to take it into account in the release planning of this API removal?
On Monday, March 18, 2019 at 1:54:05 AM UTC+1, Yoichi Osato wrote:
> still claim "will be removed in M73"Thank you for reporting. Yes it should be updated.
2019年3月17日(日) 12:26 j.j. <fri...@jeka.info>:
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Am Dienstag, 5. März 2019 07:02:10 UTC+1 schrieb Yoichi Osato:Updates: postpone API removal to M75.https://www.chromestatus.com/features/4507242028072960 (Shadow DOM V0)
https://www.chromestatus.com/feature/4642138092470272 (Custom Elements V0)
https://www.chromestatus.com/features/5144752345317376 (HTML Imports)still claim "will be removed in M73"
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PhistucK
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fau...@thexs.ca
Mason Freed
masatak...@gmail.com
On Tuesday, July 16, 2019 at 3:23:30 AM UTC+9, Mason Freed wrote:
Sorry for the delay in updating this thread. As you (and others) have mentioned, clearly these features did not get removed in M73, primarily because the usage level is still high. We have a new target removal milestone of M80, and a blog post that goes into more detail about the delay, plus gives more pointers on removing v0 dependencies:
Mason Freed
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PhistucK
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Mason Freed
On Tuesday, October 22, 2019 at 11:50:27 PM UTC-7, PhistucK wrote:
What is the reason for separating them again?
PhistucK
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Demetrios Papadopoulos
Oh. And Gerrit is now experimenting with Polymer 2... So is it basically experimenting with something deprecated? Or does it always come with a polyfill anyway (making this moot)?A bit weird since Polymer 3 exists...
- Polymer1: Shadow DOM v0 or polyfil (aka Shady DOM), CustomElements v0, HTML Imports
- Polymer2: HTML Imports (with SDv1, CEv1)
- Polymer3: None (JS modules + SDv1 + CEv1)
☆PhistucK--On Wed, Oct 23, 2019 at 8:55 PM Mason Freed <mason...@chromium.org> wrote:--
On Tuesday, October 22, 2019 at 11:50:27 PM UTC-7, PhistucK wrote:What is the reason for separating them again?Good question. This is going to be a difficult set of features to remove. Because Polymer 2 still uses HTML Imports, and the user-base for Polymer 2 is higher than for version 1, it will be easier to first get through the initial hurdles of removing Shadow DOM and Custom Elements before moving on to HTML Imports. Our plan is still to remove HTML Imports in M80.
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