1751383 - Support blocking="render"

Status: NEW

(Core :: Layout, enhancement)

Description

[Olli Pettay [:smaug][[e-mail]]]

https://github.com/whatwg/html/issues/7131
https://github.com/mozilla/standards-positions/issues/608

We need to be careful to not cause some new security/privacy issues by letting the page to block rendering forever. The current PR does let UA to unblock rendering after a timeout.

The might be other kinks in the proposal too.

Comment 1

[Simon Pieters [:zcorpan]]

Also for inline scripts: https://github.com/whatwg/html/pull/10035

Usage is still low, but seems to be increasing: https://chromestatus.com/metrics/feature/timeline/popularity/4183 currently 0.03% of page loads.

Comment 2

[r_a_m_i]

Usage is still low, but seems to be increasing: https://chromestatus.com/metrics/feature/timeline/popularity/4183 currently 0.03% of page loads.

I assume the usage is low because it's not cross-browser supported.

Currently, the usage is at ~0.1%. What is the threshold to start developing the feature?

Comment 3

[Idan]

Is there any progress on that?

Comment 4

[:klebba]

Usage has risen dramatically in recent months:
https://chromestatus.com/metrics/feature/timeline/popularity/4183

It would be great to see this feature prioritized. A clear signal of intent to implement it eventually would be helpful. This is an especially helpful mechanism for prevention of the Flash of Un-styled Content

Comment 5

[Jonathan Watt [:jwatt]]

(In reply to :klebba from comment #4)

Usage has risen dramatically in recent months:
https://chromestatus.com/metrics/feature/timeline/popularity/4183

It would be great to see this feature prioritized. A clear signal of intent to implement it eventually would be helpful. This is an especially helpful mechanism for prevention of the Flash of Un-styled Content

It was still below 1% back then in Februrary.

Chrome Platform Status shows the page loads over time now jumping up to over 10%.

(I'm not sure which of these we should be using:)
https://chromestatus.com/metrics/webfeature/timeline/popularity/12
https://chromestatus.com/metrics/feature/timeline/popularity/4183

Comment 6

[:klebba]

So one in ten page loads could benefit from support of this feature today. What other signals are needed to set a priority and signal something to developers? Thanks for considering

Comment 7

[Simon Pieters [:zcorpan]]

https://chromestatus.com/metrics/feature/timeline/popularity/4183 has now jumped to ~11% of page loads, so some big site(s) have probably started to use this. The httparchive usage is at 0.18% of pages.

Comment 8

[Daniel Veditz [:dveditz] out until Nov 10]

Probably ads... I looked at the top 4 sites listed on the chrome-stats page and they all looked like marketing landing pages for various never-heard-of-it products.

Comment 9

[:klebba]

:dveditz are you referring to the list titled "Sample URLs of the most popular sites using this feature ordered alphabetically"? If so, I recommend taking a closer look because the list is ALPHA sorted, not RANKED.

:zcorpan is correct that the usage has surged from <1% in June 2025 to >11% in October 2025.

If we study all of the 100 "sample URLs" provided, we can see among them:

images.google.com
google.com
google.com.hk
univision.com
walmart.com

It would be really great to see the dev team set a priority for this feature. The only data we have to study continues to provide super compelling evidence that developers want to adopt it. Thank you!

Comment 10

[andseier]

Just wanted to pile on that I would find this very useful as a way to reason about what resources will have been loaded into my application by the time I begin rendering. It is similar to why getting Implement CSS module scripts was so important (thanks!).

As a developer, there are typically a small-but-critical set of resources that I want to be for sure loaded by the time I start trying to render things. Right now, I have to manage those race conditions. It would be amazing to simply indicate this in my markup and offload that complexity.

Comment 11

[Daniel Holbert [:dholbert]]

[Assessing as Medium, though we're assuming of the work here is DOM work, but emilio's also familiar with the relevant code]