Optimistic Updates in React Applications

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

const updatePost = async (postData) => {
  // Assume this function sends the updated post data to your server
  // and returns the updated post data
  const response = await fetch('https://yourapi.com/posts/' + postData.id, {
    method: 'PUT',
    headers: {
      'Content-Type': 'application/json',
    },
    body: JSON.stringify(postData),
  });

  if (!response.ok) {
    throw new Error('Network response was not ok');
  }

  return response.json();
};

function PostEditor({ post }) {
  const queryClient = useQueryClient();
  const { mutate: updatePostData } = useMutation(updatePost, {
    onMutate: async (newPost) => {
      // Cancel any outgoing refetches for the posts query
      await queryClient.cancelQueries('posts');

      // Snapshot the previous value
      const previousPosts = queryClient.getQueryData('posts');

      // Optimistically update to the new value
      queryClient.setQueryData('posts', (old) => {
        return old.map((post) => post.id === newPost.id ? { ...post, ...newPost } : post);
      });

      return { previousPosts };
    },
    onError: (err, newPost, context) => {
      // Roll back to the previous value
      queryClient.setQueryData('posts', context.previousPosts);
    },
    onSettled: () => {
      // Refetch after error or success:
      queryClient.invalidateQueries('posts');
    },
  });

  const handleSubmit = (e) => {
    e.preventDefault();
    const formData = new FormData(e.target);
    const updatedPost = { id: post.id, title: formData.get('title'), content: formData.get('content') };

    updatePostData(updatedPost);
  };

  return (
    /* JSX for form fields */
    // Assume a form with title and content input fields
    // and a submit button calling handleSubmit on submit
  );
}