TypeError: Failed to fetch dynamically imported module

[IPWright83]

Describe the bug

Since switching to Vite we noticed a new production issue, where sometimes users are encountering an error if we deploy while they have an active session:

TypeError: Failed to fetch dynamically imported module

I believe this is because if any code is modified in an area that Vite would turn into a dynamic module, then the file hash changes, however when they try to visit an area that would trigger the dynamic load, those files no longer exist so they hit the error message above.

Quoting from https://stackoverflow.com/a/74057337/21061

When you dynamically import a route/component, during build it creates a separate chunk. By default, chunk filenames are hashed according to their content – Overview.abc123.js. If you don't change the component code, the hash remains the same. If the component code changes, the hash changes too - Overview.32ab1c.js. This is great for caching.

Now this is what happens when you get this error:

• You deploy the application
• Your Home chunk has a link to /overview route, which would load Overview.abc123.js
• Client visits your site
• You make changes in your code, not necessarily to the Overview component itself, but maybe to some children components that Overview imports.
• You deploy changes, and Overview is built with a different hash now - Overview.32ab1c.js
• Client clicks on /overview link - gets the Failed to fetch dynamically imported module error, because Overview.abc123.js no longer exists

That is why the errors correlate with deployments. One way to fix it is to not use lazy loaded routes, but that's not a great solution when you have many heavy routes - it will make your main bundle large

What I expect to happen, is not to encounter any errors if the users session remains active during a deployment.

I have been unable to come up with a good workaround (specifically for me using React ErrorBoundary is the best I can do so far with a re-direct similar to https://stackoverflow.com/a/74861436/21061 which is a mitigation and provides quite a poor user experience flashing an error message).

Reproduction

https://github.com/IPWright83/vite-dynamic-import

Steps to reproduce

The above repository has been set up to mimick a production deployment as obviously that is a much more complicated set-up. It leverages React.lazy to force a dynamic module and uses a setTimeout to provide a delay with which to simulate a user navigation to a page requiring a module. In a real production scenario I don't believe React.lazy is required.

• Clone the above repository

• npm install

• npm run build

• open a 2nd terminal

• Terminal 1 npx serve dist (starts a web server)

• Browser open the URL (usually localhost:3000)

• Text Editor modify src/Foo.jsx changing the string "Foo" to something else (within 30s of launching the page - increase the setTimeout in App.jsx if this is not long enough)

• Terminal 2 npm run build

Wait... 30s after loading the page you should see a blank page render with errors in the browser console:

If you were to reload the page, you can see that Foo-b53985a6.js has been renamed to Foo-535d5a10.js (or similar new hash)

System Info

❯ npx envinfo --system --npmPackages '{vite,@vitejs/*}' --binaries --browsers

  System:
    OS: Linux 5.15 Ubuntu 20.04.5 LTS (Focal Fossa)
    CPU: (12) x64 Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz
    Memory: 18.36 GB / 31.10 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.14.0 - ~/.nvm/versions/node/v16.14.0/bin/node
    Yarn: 1.22.18 - ~/.nvm/versions/node/v16.14.0/bin/yarn
    npm: 8.3.1 - ~/.nvm/versions/node/v16.14.0/bin/npm
  Browsers:
    Chrome: 109.0.5414.74
    Chromium: 109.0.5414.74
    Firefox: 109.0

### Used Package Manager

pnpm

### Logs

_No response_

### Validations

- [X] Follow our [Code of Conduct](https://github.com/vitejs/vite/blob/main/CODE_OF_CONDUCT.md)
- [X] Read the [Contributing Guidelines](https://github.com/vitejs/vite/blob/main/CONTRIBUTING.md).
- [X] Read the [docs](https://vitejs.dev/guide).
- [X] Check that there isn't [already an issue](https://github.com/vitejs/vite/issues) that reports the same bug to avoid creating a duplicate.
- [X] Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to [vuejs/core](https://github.com/vuejs/core) instead.
- [X] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/vitejs/vite/discussions) or join our [Discord Chat Server](https://chat.vitejs.dev/).
- [X] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.

[sapphi-red]

This is not something specific to Vite and happens with Webpack, too.

https://mitchgavan.com/code-splitting-react-safely/
http://dimaip.github.io/2020/04/25/deploying-apps-with-code-splitting/

I don't have any idea to solve this on a bundler side.

[awacode21]

We are experiencing the same issues with a vite+vue SSR application.
we are experiencing thousands of those a day. also multiple days after deployment... we also saw this after our very first go-live, where no "previous version" was online. We are completely desperate since one week on how to fix this.
Other strange thing is, sometimes we get this error logged in Sentry, and when we try to check if the file really is not available, we are able to access it. Others are not working

[IPWright83]

Thanks @sapphi-red, is it Vite or Rollup generating these hashes (assuming that's what they are) on the filenames? I wonder if there's a way to suppress that behaviour and if it's required for cache busting whether there's any alternative approaches.

[victorlmneves]

@sapphi-red both generate hashes when running the build. If your product it's a SPA you can try to use a service worker together with an interceptor (if you use Axios) to manage that. I did it on Vue 2 where it's basically stores on the localStorage a version of the app and then compares if the one that you access it's the same or not and if not it triggers a reload of the browser in order to get the updated version

[IPWright83]

@victorlmneves could you provide a bit of a fuller explanation/ code snippets maybe of tha so I understand the concepts a bit more? I'd be quite interested in exploring what that might look like.

[victorlmneves]

@IPWright83
https://dev.to/voodu/vue-3-pwa-service-worker-12di
https://medium.com/@FezVrasta/service-worker-updates-and-error-handling-with-react-1a3730800e6a

And here is an example that I did some years ago

import { register } from "register-service-worker"

if (process.env.NODE_ENV === "production") {
  register(`${process.env.BASE_URL}service-worker.js`, {
    ready() {
      console.log(
        "App is being served from cache by a service worker.\n" +
          "For more details, visit https://goo.gl/AFskqB"
      )
    },
    registered() {
      console.log("Service worker has been registered.")
    },
    cached() {
      console.log("Content has been cached for offline use.")
    },
    updatefound() {
      console.log("New content is downloading.")
    },
    updated() {
      console.log("New content is available please refresh.")
      caches.keys().then(names => {
        for (let name of names) {
          console.log(name)
          caches.delete(name)
        }
      })
      setTimeout(() => {
        window.location.reload()
      }, 1000)
    },
    offline() {
      console.log(
        "No internet connection found. App is running in offline mode."
      )
    },
    error(error) {
      console.error("Error during service worker registration:", error)
    }
  })
}

And another one using Axios interceptors

axios.interceptors.response.use((resp) => {
  let v = resp.headers['vers'] || 'default'

  if (v !== localStorage.getItem('vers') && resp.config.method == 'get') {
    localStorage.setItem('vers', v)
    window.location.reload() // For new version, simply reload on any get
  }

  return Promise.resolve(resp)
})

[sapphi-red]

@IPWright83
You can remove these hashes from the filename by configuring entryFileNames and chunkFileNames.

import { defineConfig } from 'vite'

export default defineConfig({
  build: {
    rollupOptions: {
      entryFileNames: '[name].js',
      chunkFileNames: '[name].js'
    }
  }
})

But yes this is recommended for cache busting.

I don't know any alternatives other than the ones described in the articles I linked above.

[victorlmneves]

@IPWright83 by the way, have you tried to access directly the file that is displayed on the console that wasn't possible to import? I'm asking because on our project we get those errors randomly but when we access them directly the file exist

[IPWright83]

I have @victorlmneves. Is there any way to adopt an approach more like this #5825 @sapphi-red? Anything after the queryString can still cache-bust, but as the file name is constant you'll get the new payload. I think that example is a little primitive (I think JS needs transforming too). Could you see any issues with this approach?

[sapphi-red]

I guess it's possbile by using a plugin.
I think that will lead to runtime errors sometimes because the dynamic import in old version files can resolve to new version files.

For example,
first version deployed

// foo.js
export const foo = 'foo'
export const bar = 'bar'

// a file depends on foo.js
import('./foo.js').then(mod => {
  if (mod.bar.startsWith('b')) {
    console.log(mod.foo)
  }
})

second version deployed

// foo.js
export const foo = 'foo'

// a file depends on foo.js
import('./foo.js').then(mod => {
  console.log(mod.foo)
})

[victorlmneves]

@IPWright83
Meanwhile, I also saw someone handling the problem this way

router.onError((error, to) => {
  if (error.message.includes('Failed to fetch dynamically imported module')) {
    window.location = to.fullPath
  }
})

[IPWright83]

@victorlmneves yeah, that works for vue-router and is in the StackOverflow link I shared. Unfortunately we're using react-router through various indirection connected-react-router & react-router-config. So even if it did expose an onError handler which I've been unable to find, we'd struggle calling it :(

[mikemklee]

Any updates on this?
Also running into the same issue with a vue 2 + vite app, when using dynamic imports.

The vue router hack could work for some imports, but we have dynamic imports outside of the router, which i don't think the hack would be able to cover.

Besides, forcing a reload because an error occurred doesn't seem like the best UX, so wondering if there's a solution/workaround that is more subtle and "behind the scenes" 🤔

[yakobe]

While I understand that we should try to solve this problem ourselves, it seems like this must be quite a fundamental problem that developers will have when creating apps with vite? Especially when continuous deployment comes into the mix, because the files update very often and trigger lots of errors. For now I am back to "nightly deployments" to try and minimize disruption 😬.

It would be great if there was a standard solution somewhere in the docs. Preferably one without making the users manually "opt-in" to a page reload. Even nicer would be if vite could somehow handle it for us so we don't have to do anything. Eg catch the error and refresh the files without a hard reload of the page. That would greatly improve the DX 🙂.

Thanks for all the great work. Vite is awesome.

[victorlmneves]

@yakobe in my case, it's not about outdated chunks. I'm getting this with existing files that is even worst to figure out the problem and try to fix it, especially because the only way I'm able to reproduce the issue it's shutting down the node server (I have SSR app) :/

[lzacharkow]

For what it's worth, an ad-blocker was the root of this issue for me. Disabling it resolved my issue.

[lmiller1990]

A lot of Cypress users run into this: cypress-io/cypress#25913

I don't think I can fix it on the Cypress end. I can spend time (several days of development resources) to patch Vite if needed, but it looks like the cause isn't entirely clear.

Some observations:

1. Happens mostly with large bundles - like MUI (Material UI).
2. Especially happens on CI with Docker + many instances running (eg, race condition/resource issue)?

Any tips -- maybe from someone more familiar with Vite - on debugging this?

I will inspect Cypress more first and keep the limitations in mind.

[benadamstyles]

We are just hitting this now too, but it's not just when the user has a browser tab open. It can also happen much later, if the user returns to our app after we have deployed. We're trying to work out if it's caused by the index.html page being cached for too long, rather than an issue with the JS file hashes themselves. Maybe it helps someone who is experiencing this? My reasoning goes like this:

• Let's say you have index.html which references index.abc.js which dynamically imports moduleX.123.js.
• You update your code and deploy it, so now you have index.def.js which dynamically imports moduleX.456.js. This should not cause any "module not found" issues because all the file hashes are new, even the entry index JS file.
• However, if your index.html file has been cached for longer, it still contains the reference to index.abc.js, which dynamically imports the now deleted moduleX.123.js. Hence you get an error.

I'm still confirming this but I wondered if it matches anyone else's experience/setup?

[AlfonsoUceda]

Happened to me after upgrading from vite 4.0.1 to 4.1.4

[adamkpurdy]

@benadamstyles I had the same issue. I removed the hashing option in the config like another user mentioned.

[aakash14goplani]

I am facing same issue with SvelteKit + Vite.

[eifr-vault]

Not sure if related but I'm getting the same error when using storybook with a react component that imports a module from an index.ts file (exports all others)

[namu254]

ad-blocker

same

[lmiller1990]

I reproduced this in CI only, you can follow my progress as I debug it in Cypress: cypress-io/cypress#25913 (comment) I suspect the same core issue. I think it's a race condition or resources related issue.

[aethr]

I think there are possibly two separate issues being described by different users/teams in this thread:

1. failed to fetch after a new deployment where the old version was deleted from the server

• in this case, attempting to load the resource referenced by the error is expected to fail, it has been deleted

2. failed to fetch that occurs somewhat randomly

• in this case, attempting to load the resource succeeds

For people experiencing issue 1., the solution is to organise your deployments so that old versions aren't deleted immediately. Doing a deployment of new app code doesn't mean that all users running your app in their browser will update immediately (unless you force it somehow).

For those users who still have an older version running in their browser (lets say index.123.js), navigating to routes that load chunks dynamically will always reference the chunk that was current when they loaded your app (ie home.123.js), and this is correct. You don't want the user getting half of their chunks with new app code and half with old, this would lead to very hard to debug issues. If you delete those chunks while the user is still navigating around the app, you will hit this error when they change routes and try to load a chunk they haven't loaded yet.

For users that load the app after a deployment, index.html will reference a new index.456.js chunk that references all the other chunks that are consistent with that version (ie home.456.js if there are also changes in that chunk). The only difference is which version was referenced by index.html when the user loaded the tab.

If you keep a manifest of each deployment, and your instrumentation/logging includes the "version" of the app users are using, you should be able to figure out how long old versions are still used. My team has seen users still operating in the same tab they loaded a month ago without updating, so we keep all our built assets deployed for a long time. If you want to force users to reload when a new version is deployed, that's a whole piece of engineering in itself.

[lmiller1990]

According to quite a bit of research in cypress-io/cypress#25913 at least one class of error is related to CI on GH Actions specifically - not sure if this helps anyone, but worth noting in case it does.

[victorlmneves]

Found this tweet related to the topic where a dev shows a solution when using React and asks for feedback where Evan You gives a reply
https://twitter.com/cpojer/status/1730141247900459166?t=yT1x3GDgin4uVW0oh1-Guw&s=31

[IraiDev]

Hello, at the moment I have a solution for the error: "Failed to fetch dynamically imported module" in React, using react-router-dom. It's worth noting that I'm on version 6.16.0 and I'm using createBrowserRouter. It is necessary to create an ErrorPage component, which should be passed to the errorElement prop of the router. I'll provide the code below.

It is necessary to use the useErrorRouter hook to capture the error, this is a react-router-dom hook.

code:

ErrorView or ErrorPage

  const ERROR_MESSAGE= "dynamically imported module"
  // this string must be exactly like this

  export default function ErrorView() {
  const error = useRouteError() as any

  const handleReaload = () => {
    window.location.reload()
  }

  console.log(error)
  if (
    error?.message &&
    (error.message as string)
      .toLocaleLowerCase()
      .includes(ERROR_MESSAGE.toLocaleLowerCase())
      // 
  ) {
    setTimeout(() => {
      handleReaload()
    }, 1000)
    // this timeout is for the returned component to be displayed for the assigned time, but you can skip it and return null if you only want to perform the reload.
    
    return <UpdateApp /> // put here your custom component error to replace "Failed to fetch dynamically imported module"
  }
  
  return <>Your base Error Page componente here...</>
}

Router

// IMPORTANT: don't use lazy import from your ErrorView or ErrorPage

  import ErrorView from "@views/error/error_view"

  export const Router = createBrowserRouter([
  {
    path: "/",
    element: <PublicLayout />,
    errorElement: <ErrorView />, // use the ErrorView OR ErrorPage
    children: [
       {
          path: "your_path",
          element: <>Example Component</>,
       }
    ],
  }
])

i'm using this react-router-dom version

   {
     "dependencies": {
       "react-router-dom": "^6.16.0",
      }
   }

Note that, most likely, the first time you implement this, it may not work. However, from the second or third time onwards, it should work because you will have this code in the cache. In previous attempts, when this solution was not present in your source code, the error persisted. Currently, it is the best solution I could apply. Hopefully, it will be helpful for you.

"I'm sorry if my English is not good."

[muhammad0071]

@aethr thanks for the complete summary of the current state!

We have found another workaround, that might be useful if having a modern chunk is not super important for you. In the nutshell the solution is this:

1. Use @vitejs/plugin-legacy and turn off modern chunks completely.
2. Legacy plugin falls back to systemjs for dynamic imports
3. And, a complete systemjs version supports onload hook and also provides an API to clear the cache failed script requests.

//vite.config.js
plugins: [
  legacy({
    renderModernChunks: false, // always use legacy chunks
    externalSystemJS: true, // do not use provided systemjs build because it does not support hooks and registry deletion API
    additionalLegacyPolyfills: ['systemjs/dist/system.min.js'], // provide a complete systemjs build
  })
]

// at the very beginning of the app entry point
if (window && window.System) {
  window.System.constructor.prototype.onload = function (isError: boolean, id: string) {
    // If the module fails to load, we want to be able to retry the loading
    // To do that, we want to remove the cached failed response from the SystemJS cache
    if (isError) {
      window.System.delete(id)
    }
  }
}

With this solution, we are able to retry the dynamic import after a network failure.

hey @malykhinvi i follow this guide but no luck, got errors like this, are that any other configs ?

[malykhinvi]

@muhammad0071 you miss types for System js. The workaround is:

declare global {
  interface Window {
    System?: any
  }
}

[cruzluna]

I enabled ssr and it fixed it for me.

// vite.config.ts

import { defineConfig } from "@solidjs/start/config";

export default defineConfig({ start: { ssr: true } });

[smk87]

I was having this issue. After much searching and trial and error, I got it fixed by removing optimizeDeps from the vite config. Previously, it was like below. I just removed the entire optimizeDeps.

    optimizeDeps: {
      exclude: ['js-big-decimal'],
    }

[dennis-gonzales]

I solved this in Athena Crisis by wrapping React.lazy with an error handler: https://twitter.com/cpojer/status/1730141247900459166

This is what ended up my solution too, many thanks!

[Ma-An]

Looks like vite emits an error when it fails to load dynamic imports. Documentation here.
Using this solution helped us to refresh when vite errored out.

[sergeushenecz]

Looks like vite emits an error when it fails to load dynamic imports. Documentation here. Using this solution helped us to refresh when vite errored out.

Did you try it ?

[Ma-An]

Looks like vite emits an error when it fails to load dynamic imports. Documentation here. Using this solution helped us to refresh when vite errored out.

Did you try it ?

Yes. We had to use the above solution instead of the posted solution in this thread:

router.onError((error, to) => {
  if (error.message.includes('Failed to fetch dynamically imported module')) {
    window.location = to.fullPath
  }
})

Issue is that Firefox has a different error message than Chrome when failing to fetch dynamic, we kept running into "Loading module from "X.js" failed due to disallowed mime type".

[sergeushenecz]

Looks like vite emits an error when it fails to load dynamic imports. Documentation here. Using this solution helped us to refresh when vite errored out.

Did you try it ?

Yes. We had to use the above solution instead of the posted solution in this thread:

router.onError((error, to) => {
  if (error.message.includes('Failed to fetch dynamically imported module')) {
    window.location = to.fullPath
  }
})

Issue is that Firefox has a different error message than Chrome when failing to fetch dynamic, we kept running into "Loading module from "X.js" failed due to disallowed mime type".

Dou you call window.reaload also right?

[ysyfff]

@IPWright83 @victorlmneves
If we can get the unique flag of the source file this problem may be solved, chunk.facadeModuleId seems to be the unique flag, unfortunately it may be null sometimes.

If someone can get the unique flag of source file, here is how to solve the problem:

1. In generateBundle hook, rename fileName as [name]${uniqueFlag}-[hash].js
2. rename bundled file name as [name]${uniqueFlag}.js
3. in nginx, rewrite [name]${uniqueFlag}-[hash].js to [name]${uniqueFlag}.js

That's all, and I think it must be sure to solve this problem.

[shkvaratskhelia]

Run with sames error issue, finally tracked down the code and find out this kind of an import:
import OptionFilter from '../../../components/utils/table/filter/OptionFilter.vue.vue' in one of the dependency component.
For some reason (we are using GitHub copilot) we got this line and the error description did not reveal the cause at all. This might help someone )

[lisonge]

For me, it was caused by AdGuard

[Jonesus]

I was having this same issue when serving the built website with NGINX in Docker when running CI tests, accessing it with parallelized Playwright Chrome instances inside GitHub Actions. Due to unrelated constraints I had limited the net.ipv4.ip_local_port_range of sysctl to contain only 1000 ports, and when I increased the port range to 2000 ports, the issue didn't occur anymore.

[derseitenschneider]

Came across this while researching the issue. It seems to have solved mine at least, so maybe it might help some of you too:
https://www.npmjs.com/package/vite-plugin-preload

[ricklancee]

I want to shine in on this: We had two issues with the chunking of vite/rollup. One like many others here was that the older files were not available anymore after a new deploy and some of the solutions in this thread helped us by forcing a refresh.

The second issue we had was that some users had an CORS issue, we were seeing Failed to fetch in our error reporting software but after testing with users it showed in the console that they got a CORS error (which don't show up in error reporting). Which was actually not a cors issue but a request to an asset being blocked (see: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSDidNotSucceed).

The reason why it was blocked was because some adblocker, plugin and/or virus scanner was blocking these files. We changed the default chunk names from [name]-[hash].js in the rollup output options to chunk-[hash].js and that resolved the issue that they were being blocked. I think it was because the [name] was included in the chunk which was sometimes something like: component.styled-[hash].js which might have confused these programs. Changing those chunks to chunk-[hash].js worked.

[mrsudarshanrai]

We were also facing the same issue after the build. We are using the vite event to track errors and force reloading while there are errors.

window.addEventListener('vite:preloadError', (event) => {
  window.location.reload() // for example, refresh the page
})

https://vitejs.dev/guide/build#load-error-handling

[ionnikovv]

Hi @mrsudarshanrai! I have a small question: I tried to use the same workaround you provided, but in my case, the vite:preloadError event is not being triggered. I placed it at the top of my index.jsx file, right after all imports. I'm curious if there are any additional hints for its usage. Thanks!

[mrsudarshanrai]

@ionnikovv It worked in ours without further configuration; I just added it in the main. tsx. We are using "vite": "4.5.2."

[videmann]

In case of this:

1. add DEPLOY_DATE variable to .env with dateTime of deploy (update it with CI/CD software before deploy)
2. Use fixed chunk names with parameter like "/components/[filename].[ext]?modified=" + process.env.DEPLOY_DATE

This method decides 2 problems:

1. Still using browser cache (between deploys)
2. using simple filenames without hash and solve problem "failed to fetch dynamically imported module" because filenames are still the same

[TripSonny]

I had a wakeup call two years ago, can anyone give me insight on this? My husband was acting shady AF, our fire stick was acting up, my Alexa was hacked, my phones hacked, my computers hacked, and things got dangerous. Pretty sure he was somehow communicating with the fire stick, as well as using it to control the IR on our cameras. I've been putting the pieces together ever since, but I'm not a programmer. Just someone trying to stay safe. Thanks.

[httpete]

I am seeing this in the latest version of vitest.
vitest-dev/vitest#5615

[Evertvdw]

@yakobe in my case, it's not about outdated chunks. I'm getting this with existing files that is even worst to figure out the problem and try to fix it, especially because the only way I'm able to reproduce the issue it's shutting down the node server (I have SSR app) :/

@victorlmneves This is also exactly what I experience. I don't use file hashes so the filenames don't change but I see these errors happen pretty often, and also usually with the same file. Did you gain any new insights regarding this? I implemented the automatic reload on this error but I would like to know why it happens in the first place.

[victorlmneves]

@Evertvdw

Well, that's the million-dollar question
Several situations can lead to failure, I even found out recently that fails/errors on third-party scripts can lead to this (iOS devices)
Do you have it happening on all major browsers or mainly on 1 or browsers?