ReferenceError: Cannot access '__WEBPACK_DEFAULT_EXPORT__' before initialization

What version of Next.js are you using?

12.0.7

What version of Node.js are you using?

14.18.1

What browser are you using?

N/A

What operating system are you using?

macOS, Alpine

How are you deploying your application?

next start

Describe the Bug

A module which imports an es module and throws an exception at the top level has the exception swallowed and a different (vastly less helpful) exception thrown instead. I am pretty confident that this is a webpack bug, but since next vendors webpack, I’m reporting here.

Expected Behavior

When a module throws an exception during initialization, the exception should be passed to the nearest user exception handler, or crash the application. Instead, a different exception is being thrown due to webpack-generated code.

To Reproduce

Create a file lib/test.ts like the following; require it from any page (I used an API page, may be relevant); request that page.

import { z } from "zod";
throw new Error("error");
export default { z };

You will see the following error in the console, without any stack trace:

error - ReferenceError: Cannot access '__WEBPACK_DEFAULT_EXPORT__' before initialization

Things to note:

1. “zod” could be replaced by any esmodule package. The root cause is that the code generated by webpack uses a dynamic import to import the code, causing to to be an async module.
2. Exporting { z } is just so that the import doesn’t get tree-shaken-away.

[luixo]

Seems like this problem is connected to esmExternals experimental feature, which is enabled by default.

I have this problem on 12.0.7 without any underlying error, just having ESM module imported in the project. Turning off experimental feature fixed the issue.

// next.config.js
module.exports = {
  ...,
  experimental: {
    esmExternals: false
  }
}

[humble-barnacle001]

I am facing the same issue in v12.0.9 but in my case surprisingly, next dev works and also deploy on Vercel platform works but somehow the local build using next build fails