Error Handling

Errors can be divided into two categories: expected errors and uncaught exceptions. This page will walk you through how you can handle these errors in your Next.js application.

Handling expected errors

Expected errors are those that can occur during the normal operation of the application, such as those from server-side form validation or failed requests. These errors should be handled explicitly and returned to the client.

Server Actions

You can use the useActionState hook to manage the state of Server Functions and handle expected errors. Avoid using try/catch blocks for expected errors. Instead, you can model expected errors as return values, not as thrown exceptions.

'use server'
 
export async function createPost(prevState: any, formData: FormData) {
  const title = formData.get('title')
  const content = formData.get('content')
 
  const res = await fetch('https://api.vercel.app/posts', {
    method: 'POST',
    body: { title, content },
  })
  const json = await res.json()
 
  if (!res.ok) {
    return { message: 'Failed to create post' }
  }
}

Then, you can pass your action to the useActionState hook and use the returned state to display an error message.

'use client'
 
import { useActionState } from 'react'
import { createPost } from '@/app/actions'
 
const initialState = {
  message: '',
}
 
export function Form() {
  const [state, formAction, pending] = useActionState(createPost, initialState)
 
  return (
    <form action={formAction}>
      <label htmlFor="title">Title</label>
      <input type="text" id="title" name="title" required />
      <label htmlFor="content">Content</label>
      <textarea id="content" name="content" required />
      {state?.message && <p aria-live="polite">{state.message}</p>}
      <button disabled={pending}>Create Post</button>
    </form>
  )
}

Server Components

When fetching data inside of a Server Component, you can use the response to conditionally render an error message or redirect.

export default async function Page() {
  const res = await fetch(`https://...`)
  const data = await res.json()
 
  if (!res.ok) {
    return 'There was an error.'
  }
 
  return '...'
}

Not found

You can call the notFound function within a route segment and use the not-found.js file to show a 404 UI.

import { getPostBySlug } from '@/lib/posts'
 
export default function Page({ params }: { params: { slug: string } }) {
  const post = getPostBySlug(params.slug)
 
  if (!post) {
    notFound()
  }
 
  return <div>{post.title}</div>
}

Handling uncaught exceptions

Uncaught exceptions are unexpected errors that indicate bugs or issues that should not occur during the normal flow of your application. These should be handled by throwing errors, which will then be caught by error boundaries.

Nested error boundaries

Next.js uses error boundaries to handle uncaught exceptions. Error boundaries catch errors in their child components and display a fallback UI instead of the component tree that crashed.

Create an error boundary by adding an error.js file inside a route segment and exporting a React component:

'use client' // Error boundaries must be Client Components
 
import { useEffect } from 'react'
 
export default function Error({
  error,
  reset,
}: {
  error: Error & { digest?: string }
  reset: () => void
}) {
  useEffect(() => {
    // Log the error to an error reporting service
    console.error(error)
  }, [error])
 
  return (
    <div>
      <h2>Something went wrong!</h2>
      <button
        onClick={
          // Attempt to recover by trying to re-render the segment
          () => reset()
        }
      >
        Try again
      </button>
    </div>
  )
}

Errors will bubble up to the nearest parent error boundary. This allows for granular error handling by placing error.tsx files at different levels in the route hierarchy.

Global errors

While less common, you can handle errors in the root layout using the global-error.js file, located in the root app directory, even when leveraging internationalization. Global error UI must define its own <html> and <body> tags, since it is replacing the root layout or template when active.

'use client' // Error boundaries must be Client Components
 
export default function GlobalError({
  error,
  reset,
}: {
  error: Error & { digest?: string }
  reset: () => void
}) {
  return (
    // global-error must include html and body tags
    <html>
      <body>
        <h2>Something went wrong!</h2>
        <button onClick={() => reset()}>Try again</button>
      </body>
    </html>
  )
}

How to handle errors