Optimistic Updates in Next.js 14: useOptimistic, Server Actions, and Automatic Rollback

Optimistic updates make apps feel instant. The UI updates immediately, then syncs with the server in the background. If the server rejects the change, the UI rolls back.

Next.js 14 has built-in support via useOptimistic. Here's how to use it correctly.

The Problem Without Optimistic Updates

Without optimistic updates:

1. User clicks 'Like'
2. UI waits 200-500ms for server
3. Server responds
4. UI updates

With optimistic updates:

1. User clicks 'Like'
2. UI updates instantly (optimistically)
3. Server request happens in background
4. On success: nothing visible changes
5. On failure: UI rolls back with error

Basic useOptimistic

'use client'
import { useOptimistic, useTransition } from 'react'
import { toggleLike } from '@/lib/actions'

interface Post {
  id: string
  likes: number
  likedByUser: boolean
}

export function LikeButton({ post }: { post: Post }) {
  const [isPending, startTransition] = useTransition()
  const [optimisticPost, setOptimisticPost] = useOptimistic(
    post,
    (state, liked: boolean) => ({
      ...state,
      likedByUser: liked,
      likes: liked ? state.likes + 1 : state.likes - 1
    })
  )

  function handleClick() {
    startTransition(async () => {
      setOptimisticPost(!optimisticPost.likedByUser) // Update UI immediately
      await toggleLike(post.id)                     // Then hit server
    })
  }

  return (
    <button
      onClick={handleClick}
      className={optimisticPost.likedByUser ? 'text-red-500' : 'text-gray-400'}
    >
      {optimisticPost.likes} Likes
    </button>
  )
}

The Server Action

// lib/actions.ts
'use server'
import { auth } from './auth'
import { db } from './db'
import { revalidatePath } from 'next/cache'

export async function toggleLike(postId: string) {
  const session = await auth()
  if (!session?.user?.id) throw new Error('Not authenticated')

  const existing = await db.like.findUnique({
    where: { userId_postId: { userId: session.user.id, postId } }
  })

  if (existing) {
    await db.like.delete({ where: { id: existing.id } })
  } else {
    await db.like.create({ data: { userId: session.user.id, postId } })
  }

  revalidatePath('/posts')
}

Optimistic List Updates

Adding items to a list without waiting for the server:

'use client'
import { useOptimistic, useRef } from 'react'
import { addComment } from '@/lib/actions'

export function CommentSection({ postId, initialComments }) {
  const [comments, addOptimisticComment] = useOptimistic(
    initialComments,
    (state, newComment) => [...state, newComment]
  )
  const formRef = useRef<HTMLFormElement>(null)

  async function handleSubmit(formData: FormData) {
    const text = formData.get('comment') as string

    // Optimistic update -- add immediately with temp ID
    addOptimisticComment({
      id: `temp-${Date.now()}`,
      text,
      author: 'You',
      createdAt: new Date().toISOString(),
      pending: true
    })

    formRef.current?.reset()
    await addComment(postId, text) // Server adds real comment
  }

  return (
    <div>
      {comments.map(comment => (
        <div key={comment.id} className={comment.pending ? 'opacity-60' : ''}>
          <strong>{comment.author}</strong>: {comment.text}
        </div>
      ))}
      <form ref={formRef} action={handleSubmit}>
        <input name="comment" placeholder="Add a comment..." />
        <button type="submit">Post</button>
      </form>
    </div>
  )
}

Optimistic Delete

'use client'
import { useOptimistic } from 'react'
import { deleteItem } from '@/lib/actions'

export function ItemList({ initialItems }) {
  const [items, removeOptimistic] = useOptimistic(
    initialItems,
    (state, idToRemove: string) => state.filter(item => item.id !== idToRemove)
  )

  return (
    <ul>
      {items.map(item => (
        <li key={item.id}>
          {item.name}
          <form action={async () => {
            removeOptimistic(item.id) // Remove immediately
            await deleteItem(item.id)  // Then delete on server
          }}>
            <button type="submit">Delete</button>
          </form>
        </li>
      ))}
    </ul>
  )
}

Error Handling and Rollback

If the Server Action throws, React automatically rolls back the optimistic state:

import { useOptimistic, useTransition } from 'react'
import { useState } from 'react'

function LikeButton({ post }) {
  const [error, setError] = useState<string | null>(null)
  const [isPending, startTransition] = useTransition()
  const [optimisticPost, setOptimisticPost] = useOptimistic(post, (state, liked) => ({
    ...state,
    likedByUser: liked,
    likes: liked ? state.likes + 1 : state.likes - 1
  }))

  function handleClick() {
    setError(null)
    startTransition(async () => {
      setOptimisticPost(!optimisticPost.likedByUser)
      try {
        await toggleLike(post.id)
      } catch (e) {
        setError('Failed to update. Please try again.')
        // Optimistic state automatically rolls back
      }
    })
  }

  return (
    <>
      <button onClick={handleClick}>{optimisticPost.likes} Likes</button>
      {error && <p className="text-red-500 text-sm">{error}</p>}
    </>
  )
}

Pre-Built in the Starter Kit

The AI SaaS Starter includes optimistic update patterns pre-implemented:

• Like/reaction buttons
• Comment forms
• Todo-style list management
• Settings toggle switches

AI SaaS Starter Kit -- $99 one-time -- interactive patterns ready to customize. Clone and ship.

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