Optimistic Updates in React: Instant UI Without Waiting for the Server

Users hate waiting. Every 100ms of perceived latency costs engagement.

Optimistic updates are the fix: update the UI immediately as if the server request already succeeded, then reconcile with reality when the response comes back.

The Pattern

Without optimistic updates:

1. User clicks 'Like'
2. Request fires
3. UI spins for 300ms
4. Like count updates

With optimistic updates:

1. User clicks 'Like'
2. Like count updates instantly
3. Request fires in background
4. If it fails, roll back

Implementation With React Query

React Query makes optimistic updates clean:

import { useMutation, useQueryClient } from '@tanstack/react-query';

function LikeButton({ postId, currentLikes }: { postId: string; currentLikes: number }) {
  const queryClient = useQueryClient();

  const likeMutation = useMutation({
    mutationFn: (postId: string) => api.likePost(postId),

    // Step 1: Optimistically update before request fires
    onMutate: async (postId) => {
      // Cancel any in-flight refetches
      await queryClient.cancelQueries({ queryKey: ['post', postId] });

      // Snapshot current value for rollback
      const previousPost = queryClient.getQueryData(['post', postId]);

      // Optimistically update
      queryClient.setQueryData(['post', postId], (old: Post) => ({
        ...old,
        likes: old.likes + 1,
        likedByMe: true,
      }));

      return { previousPost };
    },

    // Step 2: On error, roll back to snapshot
    onError: (err, postId, context) => {
      queryClient.setQueryData(['post', postId], context?.previousPost);
    },

    // Step 3: Always refetch after settle to sync with server
    onSettled: (data, error, postId) => {
      queryClient.invalidateQueries({ queryKey: ['post', postId] });
    },
  });

  return (
    <button onClick={() => likeMutation.mutate(postId)}>
      {currentLikes} likes
    </button>
  );
}

When Rollback Happens

The rollback flow:

1. onMutate: snapshot current state, apply optimistic update
2. Request fires
3. If success: onSettled invalidates and refetches (syncs with real server state)
4. If error: onError restores from snapshot, onSettled refetches

The user sees the optimistic state immediately. A failure is rare — a brief flicker back to the original state is a better UX than waiting for every response.

List Mutations

For adding/removing items in a list:

const addTodoMutation = useMutation({
  mutationFn: api.addTodo,
  onMutate: async (newTodo) => {
    await queryClient.cancelQueries({ queryKey: ['todos'] });
    const previousTodos = queryClient.getQueryData(['todos']);

    queryClient.setQueryData(['todos'], (old: Todo[]) => [
      ...old,
      { ...newTodo, id: 'temp-' + Date.now(), optimistic: true },
    ]);

    return { previousTodos };
  },
  onError: (err, newTodo, context) => {
    queryClient.setQueryData(['todos'], context?.previousTodos);
  },
  onSettled: () => queryClient.invalidateQueries({ queryKey: ['todos'] }),
});

When NOT to Use Optimistic Updates

Avoid them when:

• The operation is destructive (delete account, send payment)
• Rollback would be confusing (form submissions that navigate away)
• Server-generated values are immediately visible (IDs, timestamps)

For those cases, show a loading state and confirm on success.

Built-In With the Right Stack

Optimistic updates, React Query, tRPC, and the full modern React pattern set come pre-wired in the AI SaaS Starter Kit — so you ship responsive UIs from day one without plumbing the pieces together yourself.

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