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Failing test for double invoking Effects during hydration - #28951

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@eps1loneps1lon commented Apr 29, 2024•
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Working in render but broken in hydrateRoot.

@facebook-github-botfacebook-github-bot added CLA Signed React Core Team Opened by a member of the React Core Team labels Apr 29, 2024
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Comparing: 5f06c3d...314aff8

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8

@eps1lon
eps1lonforce-pushed the strict-effects branch 2 times, most recently from 845ebfa to acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon commented Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
container.innerHTML = ReactDOMServer.renderToString(element);

await act(() => {
ReactDOMClient.hydrateRoot(container, element);

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701

But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?

@eps1loneps1lon changed the title Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon marked this pull request as ready for review August 21, 2025 07:42
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Landed in #35961

@eps1loneps1lon closed this Apr 19, 2026
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eps1lon deleted the strict-effects branch April 19, 2026 18:17
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@eps1lon@react-sizebot@facebook-github-bot
, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
 blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
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Failing test for double invoking Effects during hydration - #28951
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Failing test for double invoking Effects during hydration#28951
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Working in render but broken in hydrateRoot.
@facebook-github-botfacebook-github-bot
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
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Landed in #35961
@eps1loneps1lon
closed this
Apr 19, 2026
@eps1lon
eps1lon
deleted the

strict-effects

branch
April 19, 2026 18:17
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
Skip to content
Failing test for double invoking Effects during hydration - #28951
Closed
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eps1lon:strict-effects
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Failing test for double invoking Effects during hydration#28951
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Working in render but broken in hydrateRoot.
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
eps1lon
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Apr 19, 2026

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Landed in #35961
@eps1loneps1lon
closed this
Apr 19, 2026
@eps1lon
eps1lon
deleted the

strict-effects

branch
April 19, 2026 18:17
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@eps1lon@react-sizebot@facebook-github-bot

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
Skip to content
Failing test for double invoking Effects during hydration - #28951
Closed
eps1lon wants to merge 1 commit into
react:mainfrom 
eps1lon:strict-effects
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Failing test for double invoking Effects during hydration#28951
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Working in render but broken in hydrateRoot.
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labels
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
eps1lon
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Apr 19, 2026

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Landed in #35961
@eps1loneps1lon
closed this
Apr 19, 2026
@eps1lon
eps1lon
deleted the

strict-effects

branch
April 19, 2026 18:17
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
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Failing test for double invoking Effects during hydration - #28951
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Failing test for double invoking Effects during hydration#28951
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Working in render but broken in hydrateRoot.
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
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marked this pull request as ready for review
August 21, 2025 07:42
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Landed in #35961
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
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Failing test for double invoking Effects during hydration - #28951
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Working in render but broken in hydrateRoot.
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
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strict-effects
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View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
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Apr 19, 2026

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Landed in #35961
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closed this
Apr 19, 2026
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strict-effects

branch
April 19, 2026 18:17
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
Skip to content
Failing test for double invoking Effects during hydration - #28951
Closed
eps1lon wants to merge 1 commit into
react:mainfrom 
eps1lon:strict-effects
Closed
Failing test for double invoking Effects during hydration#28951
eps1lon wants to merge 1 commit into
react:mainfrom 
eps1lon:strict-effects
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@eps1lon
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Apr 29, 2024•

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Working in render but broken in hydrateRoot.
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
eps1lon
commented
Apr 19, 2026

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Landed in #35961
@eps1loneps1lon
closed this
Apr 19, 2026
@eps1lon
eps1lon
deleted the

strict-effects

branch
April 19, 2026 18:17
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
Failing test for double invoking Effects during hydration by eps1lon · Pull Request #28951 · react/react · GitHub
Skip to content
Failing test for double invoking Effects during hydration - #28951
Closed
eps1lon wants to merge 1 commit into
react:mainfrom 
eps1lon:strict-effects
Closed
Failing test for double invoking Effects during hydration#28951
eps1lon wants to merge 1 commit into
react:mainfrom 
eps1lon:strict-effects
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@eps1lon
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Apr 29, 2024•

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Working in render but broken in hydrateRoot.
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Comparing: 5f06c3d...314aff8
Critical size changes
Includes critical production bundles, as well as any change greater than 2%:
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
oss-stable/react-dom/cjs/react-dom.production.js=6.68 kB6.68 kB=1.83 kB1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js=530.18 kB530.18 kB=93.39 kB93.39 kB
oss-experimental/react-dom/cjs/react-dom.production.js=6.69 kB6.69 kB=1.83 kB1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js=655.81 kB655.81 kB=115.30 kB115.30 kB
facebook-www/ReactDOM-prod.classic.js=675.58 kB675.58 kB=118.54 kB118.54 kB
facebook-www/ReactDOM-prod.modern.js=666.00 kB666.00 kB=116.86 kB116.87 kB
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB
Significant size changes
Includes any change greater than 0.2%:
Expand to show
Name+/-BaseCurrent+/- gzipBase gzipCurrent gzip
react-native/shims/ReactNativeViewConfigRegistry.js=3.69 kB3.55 kB=1.32 kB1.23 kB

Generated by 🚫 dangerJS against 314aff8
@eps1lon
eps1lonforce-pushed
the
strict-effects
branch
2 times, most recently
from
845ebfa to
acd5fccCompareApril 29, 2024 16:19
eps1lon
eps1lon
commented
Apr 29, 2024
View reviewed changes
Comment threadpackages/react-dom/src/__tests__/ReactDOMStrictEffects-test.js
 container.innerHTML = ReactDOMServer.renderToString(element);

 await act(() => {
 ReactDOMClient.hydrateRoot(container, element);
@eps1loneps1lonApr 29, 2024

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Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke: https://github.com/facebook/react/blob/94eed63c49d989861ae7cd62e111de6d717f0a10/packages/react-reconciler/src/ReactFiberWorkLoop.js#L3691-L3701
But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?
@eps1loneps1lon
changed the title
Test StrictEffects in react-domFailing test for double invoking Effects during hydrationAug 21, 2025
@eps1lon
eps1lon
marked this pull request as ready for review
August 21, 2025 07:42
@eps1lon
eps1lon
commented
Apr 19, 2026

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Landed in #35961
@eps1loneps1lon
closed this
Apr 19, 2026
@eps1lon
eps1lon
deleted the

strict-effects

branch
April 19, 2026 18:17
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@eps1lon@react-sizebot@facebook-github-bot