Prefetching Data Using QueryKeys

Illustrate how to prefetch data for a smoother user experience by leveraging QueryKeys before a component mounts.

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

function prefetchTodos() {
  const queryClient = useQueryClient();
  return queryClient.prefetchQuery(['todos'], fetchTodos);
}

This piece of code demonstrates how to define a function `prefetchTodos` that uses `useQueryClient` from React Query to prefetch data for the query key ['todos']. The function `fetchTodos` is assumed to be an asynchronous function that fetches todo items from a server.

import React, { useEffect } from 'react';
import { useQuery } from 'react-query';

function Todos() {
  const { data: todos, isLoading } = useQuery(['todos'], fetchTodos);
  
  useEffect(() => {
    prefetchTodos();
  }, []);
  
  if (isLoading) return <div>Loading...</div>;
  
  return (
    <div>{todos.map(todo => <p key={todo.id}>{todo.text}</p>)}</div>
  );
}

This code shows how a React component `Todos` uses the `useEffect` hook to call `prefetchTodos` before the component mounts, ensuring that data is prefetched for a smoother user experience. It then uses the `useQuery` hook with the same query key ['todos'] to fetch the data for display in the component. `isLoading` is used to show a loading state while the data is being fetched.