Intent to Experiment: Speculation Rules: prerender-until-script Action

[Chromestatus]

Contact emails

lin...@chromium.org

Explainer

https://github.com/WICG/nav-speculation/blob/main/prerender-until-script.md

Specification

https://wicg.github.io/nav-speculation/prerendering.html#speculation-rule-set-prerender_until_script-rules

Design docs

https://docs.google.com/document/d/18Ny-OJ5kfyxkZ8h73OGigk8B3gDnoxjH34RVcvSo5Do/edit?tab=t.szm4nrdsfrjv

Summary

This extends speculation rules to introduce a new action called prerender_until_script. It is designed as an intermediate option between the existing prefetch (which only fetches the main document) and prerender (which fully renders the page and runs all scripts). This new action will fetch and parse a page, discover and download its subresources like images and stylesheets, but will pause all script execution. When the user navigates to the page, it activates, and all the deferred scripts are then executed in order. This allows for a near-instant page load for content-heavy sites without the performance cost or side effects of running analytics or third-party scripts prematurely.

Blink component

Internals>Preload>Prerender

Web Feature ID

speculation-rules

Search tags

speculationrules, prerendering, prefetch, nostateprefetch

TAG review

https://github.com/w3ctag/design-reviews/issues/1183

TAG review status

Not applicable

Origin Trial documentation link

https://github.com/WICG/nav-speculation/blob/main/prerender-until-script.md

Risks

Interoperability and Compatibility

Other browsers do not implement this feature yet, but if should be safe because: 1. it is an optimization, so it should be no-op on other browsers 2. other browsers do not implement any of speculationrule actions yet.

Gecko: No signal

WebKit: No signal

Web developers: Positive (https://github.com/WICG/nav-speculation/issues/305) Web developers proposed that UA should implement an intermediate option between the existing prefetch and prerender actions.

Other signals:

Ergonomics

no

Activation

No. Developers should be able to easily try this feature by changing "prerender" to "prerender_until_script" following the explainer.

Security

It should be as safe as prerender action, as it pauses JavaScript execution during prerendering. One potential risk is the inline event handlers. inline event handlers will be executed normally during prerendering, it seems risky but we find websites usually put inline scripts before defining a inline event handler, and the inline script will make the parser be paused, therefore user agent has no chance to execute the inline event handlers. So, we think is is a low possibility risk, and would like to confirm with Origin Trial.

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Goals for experimentation

No information provided

Ongoing technical constraints

We assume it is ok not to handle inline event handlers differently as for now most pages put <script> tag before inline event handlers. But if it happens, we need to refine the inline event handlers' execution logic.

Debuggability

As well as other speculationrule features, this feature shows its current status on devtools.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Flag name on about://flags

prerender-until-script

Finch feature name

PrerenderUntilScript

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/u/1/issues/428500219

Measurement

Blink.UseCounter.Features

Estimated milestones

Origin trial desktop first	144
Origin trial desktop last	150
DevTrial on desktop	144
Origin trial Android first	144
Origin trial Android last	150
DevTrial on Android	144
Origin trial WebView first	144
Origin trial WebView last	150

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6324676351623168?gate=5823668919861248

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/68f20f78.050a0220.29f70d.004e.GAE%40google.com

This intent message was generated by Chrome Platform Status.