In TanStack React Query, initializing the query client outside of React components is recommended due to how React handles component rendering and state management. Here are the main reasons:
<hr>
<h3>1. Avoid Recreating the Query Client on Every Render</h3>
<ul>
<li>React components re-render often, and if you initialize the query client inside a component, it would create a new instance of the query client each time the component renders. This can lead to unexpected behavior, such as:
<ul>
<li>Losing cached data between renders.</li>
<li>Re-fetching data unnecessarily.</li>
<li>Wasting resources by creating and discarding query client instances repeatedly.</li>
</ul>
</li>
</ul>
<hr>
<h3>2. Persisting Query State</h3>
<ul>
<li>The query client is responsible for managing query caching, data fetching, and background updates. If the query client is recreated during a re-render, the state of ongoing queries and cached data will reset, defeating the purpose of caching.</li>
</ul>
<hr>
<h3>3. Ensuring a Single Source of Truth</h3>
<ul>
<li>Initializing the query client globally (outside the component) ensures that all parts of your application share the same instance. This provides a consistent and centralized store for managing server-state, which is essential for predictable application behavior.</li>
</ul>
<hr>
<h3>Best Practice Example</h3>
<pre><code class="language-jsx">// Initialize the query client outside the component
import { QueryClient, QueryClientProvider } from &#x27;@tanstack/react-query&#x27;;

const queryClient = new QueryClient();

function App() {
 return (
 &lt;QueryClientProvider client={queryClient}&gt;
 {/* Your app components */}
 &lt;/QueryClientProvider&gt;
 );
}
</code></pre>
<hr>
<h3>What Happens If You Don’t?</h3>
If you initialize the query client inside the component:
<pre><code class="language-jsx">function App() {
 const queryClient = new QueryClient(); // BAD PRACTICE

 return (
 &lt;QueryClientProvider client={queryClient}&gt;
 {/* Your app components */}
 &lt;/QueryClientProvider&gt;
 );
}
</code></pre>
<ul>
<li>Each render of <code>App</code> creates a new query client instance.</li>
<li>Data may be refetched unnecessarily.</li>
<li>Cached data will not persist across renders.</li>
<li>Performance issues and bugs may arise, especially in larger applications.</li>
</ul>
<hr>
<h3>Key Takeaway</h3>
Always initialize the query client outside React components to ensure it is a singleton and maintains its cache, states, and settings throughout the application lifecycle.

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In TanStack React Query, it is advised to initialize the query client outside of React components. This prevents recreating the query client on every render, helps in persisting query state, and ensures a single source of truth by sharing the same query client instance throughout the application. Failing to follow this practice can lead to unnecessary data refetching, loss of cached data, and potential performance issues.

Why You Should Initialize TanStack Query Client Outside React Components

What if &lt;App/&gt; will re-render only once. Like it is root component of the tree.