Fixing the “vueDemi2.effectScope is not a function” Error in Nuxt 3 + Pinia (SSR, Vercel Deploy)

If you’ve deployed a Nuxt 3 + Pinia app in SSR mode and encountered the following error:

vueDemi2.effectScope is not a function

you’re likely dealing with a tricky resolution or bundling issue that occurs in production builds. This problem is particularly prevalent with Node.js 22, a version commonly used by hosting platforms like Vercel.

Below, we outline the primary fix that has resolved this issue for many developers, along with additional workarounds if needed.

The Main Fix: Install Pinia Alongside @pinia/nuxt

The most reliable solution is to explicitly install Pinia as a direct dependency alongside @pinia/nuxt. This ensures that Nuxt’s SSR build references the correct version and format of Pinia’s files.

Steps to Implement:

1. Add Pinia to Your Dependencies
   Update your package.json:

   {
     "dependencies": {
       "nuxt": "^3.14.0",
       "@pinia/nuxt": "^0.7.0",
       "pinia": "^2.0.36"
     }
   }

1. Remove Existing Artifacts

   • Delete the node_modules directory.
   • Remove your lockfile (e.g., pnpm-lock.yaml, package-lock.json, or yarn.lock).

2. Reinstall Dependencies

   Run the appropriate command for your package manager:

   • pnpm install (or npm install / yarn install).

3. Rebuild & Redeploy

   Use consistent build commands and the same package manager in your production environment.

This approach resolves mismatched references, ensuring that the correct bundle is used during SSR and eliminating the vueDemi2.effectScope is not a function error.

Additional Workarounds (If Needed)

If the main fix does not fully resolve the issue in your environment, or if you encounter other compatibility constraints, consider the following alternatives:

A) Downgrade @pinia/nuxt

Some developers have found success by locking @pinia/nuxt to an older stable version:

{
  "dependencies": {
    "nuxt": "^3.14.0",
    "@pinia/nuxt": "0.5.5"
  }
}

This avoids problematic SSR build paths introduced in newer releases. However, note that you’ll miss out on features added since version 0.5.5.

B) Use Node.js 20 Instead of Node.js 22

If you can control your Node.js environment (e.g., by specifying the version in Vercel settings or using an .nvmrc file), switching to Node.js 20 can often eliminate this SSR resolution issue.

C) Disable SSR (Last Resort)

As a final measure, you can disable SSR in your Nuxt app by setting ssr: false in nuxt.config:

export default defineNuxtConfig({
  ssr: false
});

While this bypasses the server-side build that triggers the error, it also sacrifices SEO benefits and SSR-specific features. Use this option only if no other solutions work and your app does not heavily depend on SSR.

Conclusion

In most cases, explicitly installing Pinia alongside @pinia/nuxt and recreating your lockfile resolves the vueDemi2.effectScope is not a function error in Nuxt 3 SSR. If the issue persists, consider downgrading @pinia/nuxt, switching to Node.js 20, or disabling SSR as a temporary workaround. By ensuring proper alignment of your Pinia versions, you can achieve a stable SSR experience in your Nuxt 3 project.