Intent to Prototype: Permissions-Policy: unload
Fergal Daly
Contact emails
fer...@chromium.com, bfcache-dev
Explainer
https://github.com/fergald/docs/blob/master/explainers/permissions-policy-unload.md
Specification
https://github.com/whatwg/html/pull/7915
Summary
This feature allows pages to disable the running of unload event handlers. The goal is to :
- allow sites that have removed all unload handlers to ensure they do not accidentally add new ones
- allow sites to remove unload handlers when updating the code would is infeasible
Unload event handlers are problematic for various reasons and prevent use of BFCache on Desktop (see https://web.dev/bfcache/#never-use-the-unload-event).
Blink component
Motivation
Help sites migrate off unload event handlers and thereby improve BFCache hit-rate:
- by ensuring that once removed, handlers do not creep back in
- by providing a means to disable handlers in 3rd party iframes and script that is hard to change
Initial public proposal
https://github.com/w3c/webappsec-permissions-policy/issues/444
TAG review
https://github.com/w3ctag/design-reviews/issues/738
TAG review status
Pending
Risks
Interoperability and Compatibility
3rd-party frames that rely on unload may not work as expected when navigating away. This is solvable by the frame authors by use of alternatives to unload and is unlikely to impact users. See detailed discussion.
Gecko: Negative (https://github.com/w3c/webappsec-permissions-policy/issues/444#issuecomment-1047829132) FF objects to this (similar to sync-xhr and document-domain) because it’s providing a way to cause cross-origin interference with script. Explainer addresses this.
WebKit: No signal
Web developers: Positive
Private discussions with devs are positive. Sites that have made efforts to remove all unload handlers want to use this to prevent accidental returns. Also some providers of 3rd-party iframes which have content outside of their control (e.g. ad network) want to guarantee themselves to be unload-free.
Other signals:
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?
Debuggability
N/A
Is this feature fully tested by web-platform-tests?
No
Flag name
Requires code in //chrome?
False
Tracking bug
Estimated milestones
No milestones specified
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5760325231050752
This intent message was generated by Chrome Platform Status.