Is there any way you can provide a code sample that reproduces the problem? That error should only occur if there's a bug in React, so it'd be very helpful if we could reproduce.

I see the same error message in sentry, and the breadcrumbs show an "out of memory" error - and then further down some react errors.

Not sure if it'll be useful, but here's some the breadcrumbs.

OS: Windows 7,
Browser: Firefox 70.0
React: 16.9.0

out of memory
out of memory
08:21:52
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:21:52
sentry
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:21:52
xhr
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:21:52
sentry
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:21:53
xhr
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:21:57
xhr
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:22:22
fetch
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:23:25
xhr
Error: Minified React error #327; visit https://reactjs.org/docs/error-decoder.html?invariant=327 for the full message or use the non-minified dev environment for full errors and additional helpful warnings. 
08:23:30
xhr
08:24:39
exception
Error: Should not already be working.

To add some more data points:

I'm not seeing out of memory errors on my end.

We downgraded to React 16.10.2 and are still seeing errors. Will keep downgrading and report back.

Also to the FB team, we're happy to share Sentry reports with you.

I just updated my comment to include the React version (v16.9.0)

Edit: Also I searched outside of the last 24h and we've received this error many times.

Browser: Firefox 70.0 & 68.0
OS: Windows 10

Browser: Firefox 70.0
OS: Mac OS X 10.14

Browser: IE 11
OS: Windows 10

I am getting the exact same sentry reports, but unable to reproduce the same in VM environment.

We're seeing this in Sentry, too.

OS: Windows 10
Browser: Edge 18.18362
React 16.11.0 (from yarn.lock)

AFAICT it happens before the user did anything; here's the stack trace:

  at Lj(../node_modules/react-dom/cjs/react-dom.production.min.js:5382:1)
  at Anonymous function(../node_modules/react-dom/cjs/react-dom.production.min.js:2829:1)
  at t.unstable_runWithPriority(../node_modules/scheduler/cjs/scheduler.production.min.js:266:1)
  at fg(../node_modules/react-dom/cjs/react-dom.production.min.js:2794:1)
  at ig(../node_modules/react-dom/cjs/react-dom.production.min.js:2824:1)
  at Y(../node_modules/scheduler/cjs/scheduler.production.min.js:203:1)
  at A.port1.onmessage(../node_modules/scheduler/cjs/scheduler.production.min.js:94:1)```

@gzzo Are you by any chance in any of your componentDidMount functions attempting to update the state as the first thing to do in that function?

I was getting the error Should not already be working when I had the following line in my componentDidMount function :
this.setState({ hasLaunched: true });

Interesting. We do call setState in a couple of componentDidMount. The React docs specify this is okay though:

You may call setState() immediately in componentDidMount(). It will trigger an extra rendering, but it will happen before the browser updates the screen. This guarantees that even though the render() will be called twice in this case, the user won’t see the intermediate state. Use this pattern with caution because it often causes performance issues. In most cases, you should be able to assign the initial state in the constructor() instead. It can, however, be necessary for cases like modals and tooltips when you need to measure a DOM node before rendering something that depends on its size or position.

Hello,

We've also noticed this error in our sentry. It's only occurred once so far under these conditions:

OS: Windows 10
Browser: IE 11
React: 16.11.0

The stack trace does not appear to provide much additional info:

Error: Should not already be working.
  at Lj(webpack://[name]/./node_modules/react-dom/cjs/react-dom.production.min.js:223:104)
  at Anonymous function(webpack://[name]/./node_modules/react-dom/cjs/react-dom.production.min.js:121:110)
  at t.unstable_runWithPriority(webpack://[name]/./node_modules/scheduler/cjs/scheduler.production.min.js:18:431)
  at fg(webpack://[name]/./node_modules/react-dom/cjs/react-dom.production.min.js:120:318)
  at ig(webpack://[name]/./node_modules/react-dom/cjs/react-dom.production.min.js:121:61)
  at Y(webpack://[name]/./node_modules/scheduler/cjs/scheduler.production.min.js:17:178)
  at S.port1.onmessage(webpack://[name]/./node_modules/scheduler/cjs/scheduler.production.min.js:14:64)

How to solve this issue , i am facing this issue in windows 10. can anyone please share the solution?

I had this same issue. Was not a problem in Chrome however I received a blank screen and the error. Error: Should not already be working.
React 16.12.0
I had two(2) this.setState calls in conditional if statements in componentDidMount. This should have been ok however I removed them and figured a way to set them a little later and the error stopped. this.setState should have been ok to run in componentDidMount so I hope this gets resolved.

We also experience this issue.
React 16.12.0
OS: IOS 13.3
Browser: Safari

We have tons of cases were we call one or multiple 'setState' in 'componentDidMount'. It has never been an issue. Moving these calls to other places is not an option.

I am able to reproduce the issue when stepping through a function after a breakpoint in an otherwise working development build application.

Console output:
Error: Should not already be working. react-dom.development.js:24247
performSyncWorkOnRoot React
performSyncWorkOnRoot self-hosted:920
flushSyncCallbackQueueImpl React
unstable_runWithPriority scheduler.development.js:697
React 2
runWithPriority$2
flushSyncCallbackQueueImpl
workLoop scheduler.development.js:641
flushWork scheduler.development.js:596
performWorkUntilDeadline scheduler.development.js:203
enter event-loop.js:79
enter self-hosted:874
_pushThreadPause thread.js:256
_pauseAndRespond thread.js:851
pauseAndRespond thread.js:1049
_makeOnStep thread.js:978
authCheckState auth.js:100
createThunkMiddleware Redux
dispatch (index):1
onTryAutoSignIn App.js:42
componentDidMount App.js:17
React 6
commitLifeCycles
commitLayoutEffects
callCallback
invokeGuardedCallbackDev
invokeGuardedCallback
commitRootImpl
commitRootImpl self-hosted:975
unstable_runWithPriority scheduler.development.js:697
React 10
runWithPriority$2
commitRoot
finishSyncRender
performSyncWorkOnRoot
scheduleUpdateOnFiber
updateContainer
legacyRenderSubtreeIntoContainer
unbatchedUpdates
legacyRenderSubtreeIntoContainer
render
js index.js:51
Webpack 7
webpack_require
fn
1
webpack_require
checkDeferredModules
webpackJsonpCallback

We also experience this issue since we bumped React.

React 16.12.0
Browser: Firefox 72/73/74
OS: Window 10, Mac OS 10.0/10.10/10.14

The stack traces point us to this function call

More detail

InvalidStateError
An attempt was made to use an object that is not, or is no longer, usable

Any movement on this? I am also getting these errors in FireFox (73.0.1 (64-bit) but not in Chrome (Version 80.0.3987.122 (Official Build) (32-bit)
React - 16.12
React-Redux 7.1.3

It is happening when trying to initialize data from props:

//Parent Page
<SimpleForm sampleData = {sampleData} />

//SimpleForm.js
 componentDidMount (){
 if (this.props.sampleData) {
      this.props.initialize(this.props.sampleData);
}

Error:

performSyncWorkOnRoot React
    performSyncWorkOnRoot self-hosted:920
    flushSyncCallbackQueueImpl React
    unstable_runWithPriority scheduler.development.js:701
    React 2
        runWithPriority$2
        flushSyncCallbackQueueImpl
    workLoop scheduler.development.js:645
    flushWork scheduler.development.js:600
    performWorkUntilDeadline scheduler.development.js:197
    enter event-loop.js:79
    enter self-hosted:874
    _pushThreadPause thread.js:256
    _pauseAndRespond thread.js:851
    hit breakpoint.js:235
    componentDidMount Redux
    React 6
        commitLifeCycles
        commitLayoutEffects
        callCallback
        invokeGuardedCallbackDev
        invokeGuardedCallback
        commitRootImpl
    commitRootImpl self-hosted:975
    unstable_runWithPriority scheduler.development.js:701
    React 10
        runWithPriority$2
        commitRoot
        finishSyncRender
        performSyncWorkOnRoot
        scheduleUpdateOnFiber
        updateContainer
        legacyRenderSubtreeIntoContainer
        unbatchedUpdates
        legacyRenderSubtreeIntoContainer
        render
    js index.js:10
    Webpack 7
        __webpack_require__
        fn
        0
        __webpack_require__
        checkDeferredModules
        webpackJsonpCallback
        <anonymous>

I got the same error 'Should not already be working' because I created a pipe write stream in my dataActions, shifting the function to a util file outside the action file fixed the issue for me.

I got the same error reported on sentry

Error: Should not already be working.
  at Lj(/node_modules/react-dom/cjs/react-dom.production.min.js:223:129)
  at b(/node_modules/react-dom/cjs/react-dom.production.min.js:121:115)
  at Lf(/node_modules/scheduler/cjs/scheduler.production.min.js:18:437)
  at fg(/node_modules/react-dom/cjs/react-dom.production.min.js:120:325)
  at ig(/node_modules/react-dom/cjs/react-dom.production.min.js:121:61)
  at X(/node_modules/scheduler/cjs/scheduler.production.min.js:17:184)
  at hf2P/S.port1.onmessage(/node_modules/scheduler/cjs/scheduler.production.min.js:14:64)

User-Agent: 
Mozilla/5.0 (Windows NT 6.2; Win64; x64; rv:74.0) Gecko/20100101 Firefox/74.0

I can point to the live website where this error was reported but I cannot reproduce it manually.

Getting this error in React Native as well.
react: "16.11.0"
react-native: "0.62.2"

Based on my understanding of this reddit comment.

I think if user land code throws an error in componentDidMount, React does not reset state and next time render occurs, this Error "Should not already be working" gets thrown.

I has this issue and the problem was related toan ajax call with jquery made in componentDidMount with async parameter to false, this causes some issues with latest react release to synchronise the state I assume. setting async to true solved the issue

This happens to me if I set a breakpoint in componentDidMount, either by clicking the line number in Firefox's debugger or by calling debugger in the code.

Ok, at least in my case, this looks like a... thread-safety issue? Firefox has no problem running JavaScript event handlers while stopped at a breakpoint, causing all kinds of bizarre behavior. I must've missed the memo that JavaScript is no longer single-threaded.

@aweary Can we add some more diagnostic info, like what component React is working on, maybe that might give us some information on where to concentrate.
Right now, we are getting multiple reports about users facing App Crashes (React Native)

Just got this error in a React Native project.
"react": "16.13.1",
"react-native": "0.61.5"

@cristianoccazinsp I've created an issue on react-native repo as well, because its a different renderer: facebook/react-native#28948
Please do subscribe there as well.

Same here if we run $.ajax() in componentDidMount(). Our solution is to use a setTimeout():

{
  componentDidMount() {
    setTimeout(() => {
      $.ajax();
    }, 300);
  }
}

Hi @acdlite (sorry for tagging you here),
Just wanted to know what React features would trigger the usage of unstable_runWithPriority. Maybe that might help in figuring out what is causing this issue and help with creating a reproduction.

Hi Team,

I am facing this issue now in firefox browser. How to resolve this issue ? Any suggestion please?

My error reporting system has been reporting me this error in production for my react app https://twisti.app. anyone know what is causing it or how to fix it? the error message is not very helpful

user info:

Firefox 60.0
Windows 7
Windows

Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0

error:

error
Should not already be working.

/static/js/2.27fae31b.chunk.js at line 2

/*! For license information please see 2.27fae31b.chunk.js.LICENSE.txt */
(this.webpackJsonptwisti=this.webpackJsonptwisti||[]).push([[2],[function(e,t,n){"use strict";e.exports=n(163)},function(e,t,n){"use strict" {snip}
//# sourceMappingURL=2.27fae31b.chunk.js.map

trace:

Status | internal_error
-- | --
Trace ID | 26d237fb8f5a4643b2fa8fc001a47e59
Span ID | ae29218588485a11
Operation Name | pageload

This happens to me if I set a breakpoint in componentDidMount, either by clicking the line number in Firefox's debugger or by calling debugger in the code.

same with me, when i set a breakpoint between setState and Axios request in componentDidUpdate, this error will appear. But if i delete the breakpoint, everything is fine.

Also seeing this reported all of a sudden by my application monitoring service.
All on Windows 10 and Firefox 80 so far.

Also having this problem. This only happened in Firefox for me; couldn't reproduce in Chrome (dev version 87).

Tried to isolate it - as far as I can tell, after a call to setState in componentDidMount, invoking the debugger anywhere in that method after that call will cause the error, and anywhere in subsequent calls to componentDidMount in any component, including subsequent children, parent components (since a parent calls its componentDidMount after its children) and even higher up & down the hierarchy (I tried as distant as two components with a common grandparent, still caused the error).

I tested this both with a Create React App project I was already working on, and a pretty barebones test project (only React, Babel, Webpack) and the error occurred in both, which both had the latest version of React as of this writing installed (16.13.1). Tested in the current Firefox release, 81.0.1, and the current Firefox Developer Edition, 82.0b7, no difference. All on Windows 10, version 2004 (build 19041.508, really hope that doesn't matter though).

Hope this helps.

I was able to reproduce the bug after updating the dependencies on my test project to React 17.0.1. (Tested on Firefox 82.0, release channel.)

It appears when I use alert in componentDidMount. React 17.0.1

Seen this on error reports as well. Code is on React 17.0.1, user was using firefox 83 on ubuntu. No idea what triggered it though.

We are seeing sentry reports of this error, too. All our instances appear to be with Chrome 83.0.4103 on Windows 7. As others have mentioned it's reproducible with breakpoint or alert in Firefox. I have been unable to repro with Chrome. A function component seem to work in Firefox & Chrome.

Quick sandbox, if someone wants to play around:
https://codesandbox.io/s/should-not-already-be-working-bl72j?file=/src/index.js

Only have this issue in Firefox. React version 17.0.1. Like many, I have a couple jquery's ajax calls in componentDidMount

@guoyunhe's setTimeout workaround worked for me.

Same here if we run $.ajax() in componentDidMount(). Our solution is to use a setTimeout():

{
  componentDidMount() {
    setTimeout(() => {
      $.ajax();
    }, 300);
  }
}

I have this in 17.0.1 when debugging

Interestingly this error "replaces" the original one which I'm working on "TypeError: projectDataPromise.cancel is not a function" at least the displayed stacks seem the same

Firefox developer edition 85.0b4 (64-bit)

Does anyone have reliable reproduction steps? We can't really help without them.

I has this issue and the problem was related to an ajax call with jquery made in componentDidMount with async parameter to false, the réponse of tha call updated the state, this causes some issues with latest react release to synchronise the state I assume. setting async to true solved the issue

See codesandbox above - run in firefox.

Oh nice. Thanks.

All right, so the consistent repro is:

1. Open https://codesandbox.io/s/should-not-already-be-working-bl72j?file=/src/index.js in Firefox
2. Observe the error message

There is some kind of timing assumption that gets broken by the alert() being a blocking call. I don't know where the problem is. Does anyone want to dive in the source and figure it out?