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TypeError: Cannot assign to read only property 'push' of object '[object Array]' in Next.js 15.3.1 App Router #78823

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Michael-Grupp opened this issue May 4, 2025 · 1 comment
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TypeError: Cannot assign to read only property 'push' of object '[object Array]' in Next.js 15.3.1 App Router #78823

Michael-Grupp opened this issue May 4, 2025 · 1 comment
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invalid link The issue was auto-closed due to a missing/invalid reproduction link. A new issue should be opened.

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@Michael-Grupp
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I am encountering an issue when using Next.js 15.3.1 with the App Router. The error is:

TypeError: Cannot assign to read only property 'push' of object '[object Array]'
    at 64486 (../client/app-index.tsx:149:33)
    at r (app:///_next/static/chunks/webpack-2558487ccd811f16.js:1:495)
    at hydrate (../client/app-next.ts:9:23)
    at r (../client/app-bootstrap.ts:78:5)
    at appBootstrap (../client/app-bootstrap.ts:20:12)
    ...

This error seems to be caused by this code in the Next.js internals:

const nextServerDataLoadingGlobal = (self.__next_f = self.__next_f || [])
nextServerDataLoadingGlobal.push = nextServerDataCallback

This is attempting to overwrite the .push() method on the array self.__next_f, which is causing a TypeError. It happens because the .push() method is being set to nextServerDataCallback, but the __next_f array appears to be frozen or immutable in some environments (like when certain browser extensions or security measures are in place).

Steps to Reproduce

  1. Use Next.js 15.3.1 with the App Router.
  2. Enable streaming or SSR functionality, especially with server data being passed to the client.
  3. Observe the error when certain automated traffic, bot detection tools, or browser extensions that manipulate or freeze runtime globals access your site.

Actual Behavior

The .push() method is being overwritten, which causes a `TypeError in environments where the array is frozen or protected. This results in a failed hydration process, as the client-side JavaScript cannot properly register the server-side data chunks.

Expected Behavior

Next.js should handle the __next_f array correctly without attempting to overwrite its .push() method or modify it in a way that triggers a TypeError. The .push() method should be left intact, and if modification is needed, an alternative approach should be used.

Provide environment

Operating System:
Platform: darwin
Arch: arm64
Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:46 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T8112
Available memory (MB): 24576
Available CPU cores: 8
Binaries:
Node: 22.15.0
npm: 10.9.2
Yarn: 1.22.19
pnpm: N/A
Relevant Packages:
next: 15.3.1 // Latest available version is detected (15.3.1).
eslint-config-next: 15.3.1
react: 19.1.0
react-dom: 19.1.0
typescript: 5.8.3
Next.js Config:
output: N/A

Additional context

  • The error seems to be more prominent when certain automated traffic or bots (such as those using AWS EC2 IPs) are involved.
  • This issue may be related to browser extensions or other security features that prevent JavaScript from modifying global objects.
  • The error does not occur consistently in all environments and is more likely to occur under specific traffic conditions.
@github-actions github-actions bot closed this as completed May 4, 2025
@github-actions github-actions bot added the invalid link The issue was auto-closed due to a missing/invalid reproduction link. A new issue should be opened. label May 4, 2025
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github-actions bot commented May 4, 2025

We could not detect a valid reproduction link. Make sure to follow the bug report template carefully.

Why was this issue closed?

To be able to investigate, we need access to a reproduction to identify what triggered the issue. We need a link to a public GitHub repository (template for App Router, template for Pages Router), but you can also use these templates: CodeSandbox: App Router or CodeSandbox: Pages Router.

The bug template that you filled out has a section called "Link to the code that reproduces this issue", which is where you should provide the link to the reproduction.

  • If you did not provide a link or the link you provided is not valid, we will close the issue.
  • If you provide a link to a private repository, we will close the issue.
  • If you provide a link to a repository but not in the correct section, we will close the issue.

What should I do?

Depending on the reason the issue was closed, you can do the following:

  • If you did not provide a link, please open a new issue with a link to a reproduction.
  • If you provided a link to a private repository, please open a new issue with a link to a public repository.
  • If you provided a link to a repository but not in the correct section, please open a new issue with a link to a reproduction in the correct section.

In general, assume that we should not go through a lengthy onboarding process at your company code only to be able to verify an issue.

My repository is private and cannot make it public

In most cases, a private repo will not be a sufficient minimal reproduction, as this codebase might contain a lot of unrelated parts that would make our investigation take longer. Please do not make it public. Instead, create a new repository using the templates above, adding the relevant code to reproduce the issue. Common things to look out for:

  • Remove any code that is not related to the issue. (pages, API routes, components, etc.)
  • Remove any dependencies that are not related to the issue.
  • Remove any third-party service that would require us to sign up for an account to reproduce the issue.
  • Remove any environment variables that are not related to the issue.
  • Remove private packages that we do not have access to.
  • If the issue is not related to a monorepo specifically, try to reproduce the issue without a complex monorepo setup

I did not open this issue, but it is relevant to me, what can I do to help?

Anyone experiencing the same issue is welcome to provide a minimal reproduction following the above steps by opening a new issue.

I think my reproduction is good enough, why aren't you looking into it quickly?

We look into every Next.js issue and constantly monitor open issues for new comments.

However, sometimes we might miss one or two due to the popularity/high traffic of the repository. We apologize, and kindly ask you to refrain from tagging core maintainers, as that will usually not result in increased priority.

Upvoting issues to show your interest will help us prioritize and address them as quickly as possible. That said, every issue is important to us, and if an issue gets closed by accident, we encourage you to open a new one linking to the old issue and we will look into it.

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