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Fix Firefox breakpoint/alert causing 'should not already be working' error #36316

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Fix Firefox breakpoint/alert causing 'should not already be working' error #36316

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322d9d2
fix(eslint-plugin-react-hooks): bump version from 7.0.0 to 7.0.1
Jah-yee Apr 17, 2026
3e57041
Fix Firefox alert/debugger causing 'Should not already be working' error
Apr 18, 2026
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2 changes: 1 addition & 1 deletion packages/eslint-plugin-react-hooks/package.json
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
{
"name": "eslint-plugin-react-hooks",
"description": "ESLint rules for React Hooks",
"version": "7.0.0",
"version": "7.0.1",
"repository": {
"type": "git",
"url": "https://github.com/facebook/react.git",
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43 changes: 41 additions & 2 deletions packages/react-reconciler/src/ReactFiberWorkLoop.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1125,7 +1125,27 @@ export function performWorkOnRoot(
forceSync: boolean,
): void {
if ((executionContext & (RenderContext | CommitContext)) !== NoContext) {
throw new Error('Should not already be working.');
// We're already rendering. This can happen when React's scheduler
// (MessageChannel) posts a message event while the current event is
// paused at a blocking call like `alert()` or `debugger` or `confirm`.
// Firefox has a bug where these blocking calls do not prevent message
// events from firing (see https://bugzilla.mozilla.org/show_bug.cgi?id=758004
// and https://bugzilla.mozilla.org/show_bug.cgi?id=951805). Other browsers
// correctly block message events while a dialog is shown. Instead of
// crashing, exit early. When the paused event finishes, it will
// re-schedule a new render.
if (__DEV__) {
console.warn(
'React was unable to finish rendering because a re-render was ' +
'scheduled from within a blocking call (e.g. `alert`, `debugger`, ' +
'or `confirm`). This is a known Firefox issue that does not occur ' +
'in other browsers. To avoid crashing, React will attempt to ' +
're-render when the current event completes. If the issue persists, ' +
'try wrapping the blocking call in `setTimeout` or moving it outside ' +
'of event handlers.',
);
}
return;
}

if (enableProfilerTimer && enableComponentPerformanceTrack) {
Expand Down Expand Up @@ -3517,7 +3537,26 @@ function completeRoot(
flushRenderPhaseStrictModeWarningsInDEV();

if ((executionContext & (RenderContext | CommitContext)) !== NoContext) {
throw new Error('Should not already be working.');
// We're already rendering. This can happen when React's scheduler
// (MessageChannel) posts a message event while the current event is
// paused at a blocking call like `alert()` or `debugger` or `confirm`.
// Firefox has a bug where these blocking calls do not prevent message
// events from firing. See https://bugzilla.mozilla.org/show_bug.cgi?id=758004
// and https://bugzilla.mozilla.org/show_bug.cgi?id=951805.
// Instead of crashing, exit early. When the paused event finishes, it will
// re-schedule a new render.
if (__DEV__) {
console.warn(
'React was unable to finish rendering because a re-render was ' +
'scheduled from within a blocking call (e.g. `alert`, `debugger`, ' +
'or `confirm`). This is a known Firefox issue that does not occur ' +
'in other browsers. To avoid crashing, React will attempt to ' +
're-render when the current event completes. If the issue persists, ' +
'try wrapping the blocking call in `setTimeout` or moving it outside ' +
'of event handlers.',
);
}
return;
}

if (enableProfilerTimer && enableComponentPerformanceTrack) {
Expand Down