TypeError: Cannot read properties of null (reading 'length') #43143
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I somehow think this is a minification issue, because when I looked at the code there was a guard for the length check closest to the offending line, on the source code, but not in the minified code... it's a bit hard to trigger, usually you need to make a syntax error on a page, save, and fix the error to trigger it, but it doesn't always happen to me. |
ijjk
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Nov 22, 2022
…43145) After upgrading to Next.js 13, we started seeing the following HMR errors: ```sh $ next dev # ... warn - Fast Refresh had to perform a full reload. Read more: https://nextjs.org/docs/basic-features/fast-refresh#how-it-works TypeError: Cannot read properties of null (reading 'length') at eval (webpack-internal:///./node_modules/next/dist/client/dev/error-overlay/hot-dev-client.js:262:55) ``` This error appears related to the changes made in #42350 (cc @alexkirsz). It appears that `module.hot.check` will pass `null` when there are no updates: ```ts /** * Throws an exceptions if status() is not idle. * Check all currently loaded modules for updates and apply updates if found. * If no update was found, the callback is called with null. * If autoApply is truthy the callback will be called with all modules that were disposed. * apply() is automatically called with autoApply as options parameter. * If autoApply is not set the callback will be called with all modules that will be disposed on apply(). * @param autoApply */ check(autoApply?: boolean): Promise<null|ModuleId[]>; ``` When `updatedModules` is `null`, we skip the `apply()` call as this was producing `apply() is only allowed in ready status (state: idle)` errors. This matches [the prior behavior when `autoApply` was enabled](https://github.com/webpack/webpack/blob/8241da7f1e75c5581ba535d127fa66aeb9eb2ac8/lib/hmr/HotModuleReplacement.runtime.js#L266-L272). Fixes #43143. Also reported on Stack Overflow: - https://stackoverflow.com/questions/74415937/nextjs-typeerror-cannot-read-properties-of-null-reading-length - https://stackoverflow.com/questions/74504229/nextjs-v-13-typeerror-cannot-read-properties-of-null-reading-length I tested this change locally and no longer see these HMR errors. ## Bug - [X] Related issues linked using `fixes #number` - no related issues - [X] Integration tests added - there aren't any existing tests, afaict - [X] Errors have a helpful link attached, see `contributing.md` - N/A Co-authored-by: JJ Kasper <[email protected]>
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Thanks for fixing. I also just noticed this locally too. ed2aa9f?diff=unified#diff-e676ab1125f4857b4e42850e2f067267f5fb2fbbf7464b88e70a7399d9a1940bR179 looks like the line that is most critical in this fix to me. |
jankaifer
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Nov 23, 2022
…ercel#43145) After upgrading to Next.js 13, we started seeing the following HMR errors: ```sh $ next dev # ... warn - Fast Refresh had to perform a full reload. Read more: https://nextjs.org/docs/basic-features/fast-refresh#how-it-works TypeError: Cannot read properties of null (reading 'length') at eval (webpack-internal:///./node_modules/next/dist/client/dev/error-overlay/hot-dev-client.js:262:55) ``` This error appears related to the changes made in vercel#42350 (cc @alexkirsz). It appears that `module.hot.check` will pass `null` when there are no updates: ```ts /** * Throws an exceptions if status() is not idle. * Check all currently loaded modules for updates and apply updates if found. * If no update was found, the callback is called with null. * If autoApply is truthy the callback will be called with all modules that were disposed. * apply() is automatically called with autoApply as options parameter. * If autoApply is not set the callback will be called with all modules that will be disposed on apply(). * @param autoApply */ check(autoApply?: boolean): Promise<null|ModuleId[]>; ``` When `updatedModules` is `null`, we skip the `apply()` call as this was producing `apply() is only allowed in ready status (state: idle)` errors. This matches [the prior behavior when `autoApply` was enabled](https://github.com/webpack/webpack/blob/8241da7f1e75c5581ba535d127fa66aeb9eb2ac8/lib/hmr/HotModuleReplacement.runtime.js#L266-L272). Fixes vercel#43143. Also reported on Stack Overflow: - https://stackoverflow.com/questions/74415937/nextjs-typeerror-cannot-read-properties-of-null-reading-length - https://stackoverflow.com/questions/74504229/nextjs-v-13-typeerror-cannot-read-properties-of-null-reading-length I tested this change locally and no longer see these HMR errors. ## Bug - [X] Related issues linked using `fixes #number` - no related issues - [X] Integration tests added - there aren't any existing tests, afaict - [X] Errors have a helpful link attached, see `contributing.md` - N/A Co-authored-by: JJ Kasper <[email protected]>
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This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you. |
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Verify canary release
Provide environment information
Operating System:
Platform: win32
Arch: x64
Version: Windows 10 Home
Binaries:
Node: 16.14.2
npm: N/A
Yarn: N/A
pnpm: N/A
Relevant packages:
next: 13.0.5-canary.2
eslint-config-next: 13.0.4
react: 18.2.0
react-dom: 18.2.0
What browser are you using? (if relevant)
No response
How are you deploying your application? (if relevant)
No response
Describe the Bug
I just updated an existing Next app to the latest next 13 and in the console when I run yarn dev I see an error:
I don't think this is coming from my code as I only use length in one place and it should be ok.
I googled it and came up with a few people on SO that have the issue (in the last week or so) but I don't see any thing in here about it: https://stackoverflow.com/questions/74415937/nextjs-typeerror-cannot-read-properties-of-null-reading-length
Nothing seems broken, I just see it in the console.
Expected Behavior
no error message in console
Link to reproduction - Issues with a link to complete (but minimal) reproduction code will be addressed faster
n/a
To Reproduce
for me it is simply doing yarn dev,
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