React 19 & Next.js Server Actions

How to Fix React 19 "useActionState" Stuck in Pending State & Unhandled Server Action Exceptions

Diagnose and resolve React 19 useActionState infinite loading spinners, server action promise rejection hangs, and optimistic state rollbacks.

Arun Gupta
Written & technically audited by Arun Gupta, Principal Distributed Systems Architect
Verified on September 19, 2026 • Tested on Chrome 134, Safari 18.3 & Firefox 135
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⚠️ Browser Console Error & Runtime Stack Trace
❌ Form submit button disabled indefinitely with isPending === true after an unhandled server error
❌ Console warning: An action was submitted but never completed or resolved
❌ useOptimistic state fails to rollback after a server action throws an exception

1. Root Cause Analysis (Engine-Level Breakdown)

When modern JavaScript engines (V8 in Chrome/Node.js, JavaScriptCore in Safari, and SpiderMonkey in Firefox) encounter this failure condition, execution halts or falls back to degraded behavior due to the following primary triggers:

In high-scale production systems, this error rarely occurs during local development because local environments lack network latency, third-party browser extensions, complex caching proxies, and production minification transforms that uncover timing race conditions.

2. Verified Production Solutions

The following code recipes provide immediate and architectural fixes for this error:

JAVASCRIPT 
// React 19 / Next.js 15 Server Action Best Practice:
'use server';

export type ActionState = {
  success: boolean;
  message?: string;
  errors?: Record<string, string[]>;
};

export async function submitRegistration(prevState: ActionState, formData: FormData): Promise<ActionState> {
  try {
    const email = formData.get('email') as string;
    if (!email || !email.includes('@')) {
      return { success: false, errors: { email: ['Please provide a valid email address'] } };
    }

    await saveUserToDatabase(email);
    return { success: true, message: 'Registration complete!' };
  } catch (err: any) {
    console.error('[Action Error]:', err);
    // Always return structured state rather than throwing unhandled errors
    return { success: false, message: err.message || 'An unexpected error occurred.' };
  }
}

// In React 19 Client Component:
'use client';
import { useActionState } from 'react';

export function RegistrationForm() {
  const [state, formAction, isPending] = useActionState(submitRegistration, { success: false });

  return (
    <form action={formAction}>
      <input name="email" type="email" required />
      <button type="submit" disabled={isPending}>
        {isPending ? 'Submitting...' : 'Register'}
      </button>
      {state.message && <p className={state.success ? 'text-green-500' : 'text-red-500'}>{state.message}</p>}
    </form>
  );
}
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3. Step-by-Step Resolution Workflow

Follow this structured checklist to resolve and prevent this error in your CI/CD pipeline:

Step 1: Catch all exceptions in Server Actions and return state

Wrap action logic in try/catch and return a structured object instead of letting unhandled errors crash the action.

Step 2: Do not catch NEXT_REDIRECT exceptions

Allow Next.js internal redirect exceptions to bubble up without intercepting them.

Step 3: Provide matching initial state in useActionState

Ensure initialState matches the exact shape of your ActionState return interface.

🔍 How ReMOAT Resolves This Error Where It Actually Happens

Inspect the exact server action request payload, status code, and client state updates live in the ReMOAT console.

Inspect This Bug in ReMOAT DevTools →
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