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React Example: Default Query Function

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public
src
- index.tsx
.eslintrc
.gitignore
README.md
index.html
package.json
tsconfig.json
vite.config.ts

tsx

    import React from 'react'
    import ReactDOM from 'react-dom/client'
    import {
      QueryClient,
      QueryClientProvider,
      useQuery,
      useQueryClient,
    } from '@tanstack/react-query'
    import { ReactQueryDevtools } from '@tanstack/react-query-devtools'
    import type { QueryKey } from '@tanstack/react-query'

    type Post = {
      id: number
      title: string
      body: string
    }

    // Define a default query function that will receive the query key
    const defaultQueryFn = async ({ queryKey }: { queryKey: QueryKey }) => {
      const response = await fetch(
        `https://jsonplaceholder.typicode.com${queryKey[0]}`,
      )
      return await response.json()
    }

    // provide the default query function to your app via the query client
    const queryClient = new QueryClient({
      defaultOptions: {
        queries: {
          queryFn: defaultQueryFn,
        },
      },
    })

    function App() {
      const [postId, setPostId] = React.useState(-1)

      return (
          <p>
            As you visit the posts below, you will notice them in a loading state
            the first time you load them. However, after you return to this list and
            click on any posts you have already visited again, you will see them
            load instantly and background refresh right before your eyes!{' '}
            <strong>
              (You may need to throttle your network speed to simulate longer
              loading sequences)
            </strong>
          </p>
          {postId > -1 ? (
          ) : (
          )}
      )
    }

    function Posts({
      setPostId,
    }: {
      setPostId: React.Dispatch<React.SetStateAction<number>>
    }) {
      const queryClient = useQueryClient()

      // All you have to do now is pass a key!
      const { status, data, error, isFetching } = useQuery<Array<Post>>({
        queryKey: ['/posts'],
      })

      return (
          <h1>Posts</h1>
            {status === 'pending' ? (
              'Loading...'
            ) : status === 'error' ? (
              <span>Error: {error.message}</span>
            ) : (
              <>
                  {data.map((post) => (
                    <p key={post.id}>
                      <a
                        onClick={() => setPostId(post.id)}
                        href="#"
                        style={
                          // We can use the queryCache here to show bold links for
                          // ones that are cached
                          queryClient.getQueryData([`/posts/${post.id}`])
                            ? {
                                fontWeight: 'bold',
                                color: 'green',
                              }
                            : {}
                        }
                      >
                        {post.title}
                      </a>
                    </p>
                  ))}
                <div>{isFetching ? 'Background Updating...' : ' '}</div>
              </>
            )}
      )
    }

    function Post({
      postId,
      setPostId,
    }: {
      postId: number
      setPostId: React.Dispatch<React.SetStateAction<number>>
    }) {
      // You can even leave out the queryFn and just go straight into options
      const { status, data, error, isFetching } = useQuery<Post>({
        queryKey: [`/posts/${postId}`],
        enabled: !!postId,
      })

      return (
            <a onClick={() => setPostId(-1)} href="#">
              Back
            </a>
          {!postId || status === 'pending' ? (
            'Loading...'
          ) : status === 'error' ? (
            <span>Error: {error.message}</span>
          ) : (
            <>
              <h1>{data.title}</h1>
                <p>{data.body}</p>
              <div>{isFetching ? 'Background Updating...' : ' '}</div>
            </>
          )}
      )
    }

    const rootElement = document.getElementById('root') as HTMLElement
    ReactDOM.createRoot(rootElement).render(<App />)

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