Noam Rosenthal noamr

Compat impact of omitting subframe detachment events on DOM removal (whatwg/html#10194)

Proposed change: Stop synchronously firing pagehide, visibilitychange (webkitvisibilitychange), and unload inside nested browsing contexts (<iframe>, <frame>, <object>, <embed>) when removed from the DOM (FrameDetachType::kRemove), either across all subframes (Option 1, matching the HTML Standard and Chromium's OmitSubframeDetachmentEventsOnRemoval runtime flag) or only when the detaching subframe can synchronously script an ancestor document (SecurityOrigin::CanAccess any ancestor LocalFrame — Option 2b).

Summary

Crawl exposure (queries/crawl_pages_counters.csv): In the October 2026 HTTP Archive crawl (2026-10-01, is_root_page = TRUE), PageHideFired (2227) or DocumentUnloadFired (203) fired during page load on 474,165 of 15,366,242 mobile root pages (3.086%, including 57 CrUX top-1,000 pages) and 385,701 of 11,650,352 desktop root pages (3.311%, *52

Self-Review Questionnaire: Security and Privacy

What information does this feature expose, and for what purposes?

N/A

Do features in your specification expose the minimum amount of information

Importing a script from external script:

// script.js
export const something = "foo";

// importing
import {something} from "script.js"

Importing a style from an external style, with @sheet:

Self-Review Questionnaire: Security and Privacy

What information does this feature expose, and for what purposes?

It does not expose information.

Do features in your specification expose the minimum amount of information necessary to implement the intended functionality?

VT and types: fallbacks

The use-case: a page where elements transition to each other, but only if they're loaded. If the page is only partially loaded without those elements, the whole root elements transitions with a fade.

Old document:

@view-transition {
 navigation: auto;

	<!-- replace all (no markers) -->

	<div sink="container">
	Loading...
	</div>

	<template for="container">
	<p>result 1</p>
	<p>result 2</p>
	</template>

	async function after_next_paint() {
	const p = document.createElement("p");
	p.innerText = "1"
	p.style.transform = "rotateX(90deg)";
	p.style.pointerEvents = "none";
	p.style.position = "fixed";
	p.style.left = "0";
	p.style.top = "0";
	p.setAttribute("elementtiming", "foo");
	document.body.append(p);

	const track = new PerformanceTrack();

	// At some point
	track.mark(name);

	// At some other point
	track.mark(name);

	// Combines mark->mark as a single entry with duration
	track.measure(name);


	const next_frame = () => Promise(resolve => requestAnimationFrame(ts => resolve(ts));

	async function get_img_presentation_time(img) {
	// Wait until image is fully loaded
	await new Promise(resolve => img.complete ? resolve() : img.addEventListener("load", resolve))

	let frame_timestamp = await next_frame();

	// Wait until we have the frame timestamp soonest after the image was decoded.

	const events = [];
	let current_dequeue_end = 0;
	function dequeue() {
	// Ready to process, will send all current events.
	current_dequeue_end = events.length;
	fetchLater(makeURL(events)).then(({activated}) => {
	if (activated) {
	// Success, remove processed sub-array from the array and reset the index.
	events.splice(0, current_deque_end);
	current_dequeue_end = 0;