Fix: Resolve 'useEffect' error

The error "Uncaught TypeError: Cannot read properties of null (reading 'useEffect')" was occurring. This commit addresses the issue.

src/App.tsx

@@ -1,4 +1,5 @@
 
+import React from "react";
 import { Toaster } from "@/components/ui/toaster";
 import { Toaster as Sonner } from "@/components/ui/sonner";
 import { TooltipProvider } from "@/components/ui/tooltip";
@@ -10,6 +11,7 @@ import Categorias from "./pages/Categorias";
 import Calendario from "./pages/Calendario";
 import NotFound from "./pages/NotFound";
 
+// Create a client
 const queryClient = new QueryClient({
   defaultOptions: {
     queries: {
@@ -19,23 +21,27 @@ const queryClient = new QueryClient({
   },
 });
 
-const App = () => (
-  <QueryClientProvider client={queryClient}>
-    <TooltipProvider>
-      <Toaster />
-      <Sonner />
-      <BrowserRouter>
-        <Routes>
-          <Route path="/" element={<Index />} />
-          <Route path="/transacoes" element={<Transacoes />} />
-          <Route path="/categorias" element={<Categorias />} />
-          <Route path="/calendario" element={<Calendario />} />
-          {/* Adicione novas rotas acima desta linha */}
-          <Route path="*" element={<NotFound />} />
-        </Routes>
-      </BrowserRouter>
-    </TooltipProvider>
-  </QueryClientProvider>
-);
+const App = () => {
+  return (
+    <React.StrictMode>
+      <QueryClientProvider client={queryClient}>
+        <TooltipProvider>
+          <Toaster />
+          <Sonner />
+          <BrowserRouter>
+            <Routes>
+              <Route path="/" element={<Index />} />
+              <Route path="/transacoes" element={<Transacoes />} />
+              <Route path="/categorias" element={<Categorias />} />
+              <Route path="/calendario" element={<Calendario />} />
+              {/* Adicione novas rotas acima desta linha */}
+              <Route path="*" element={<NotFound />} />
+            </Routes>
+          </BrowserRouter>
+        </TooltipProvider>
+      </QueryClientProvider>
+    </React.StrictMode>
+  );
+};
 
 export default App;

src/components/ui/use-toast.ts

@@ -1,3 +1,4 @@
+
 import { useToast, toast } from "@/hooks/use-toast";
 
 export { useToast, toast };

src/main.tsx

@@ -1,5 +1,17 @@
-import { createRoot } from 'react-dom/client'
-import App from './App.tsx'
-import './index.css'
 
-createRoot(document.getElementById("root")!).render(<App />);
+import React from 'react';
+import { createRoot } from 'react-dom/client';
+import App from './App.tsx';
+import './index.css';
+
+const rootElement = document.getElementById("root");
+
+if (!rootElement) {
+  throw new Error("Root element not found!");
+}
+
+createRoot(rootElement).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+);