<React.StrictMode><!DOCTYPE html>
<html>
<head>
<script src="https://unpkg.com/react@18/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@18/umd/react-dom.development.js" crossorigin></script>
<script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
</head>
<body>
<div id="root"></div>
<script type="text/babel">
function App() {
React.useEffect(() => {
alert(0);
}, []);
return (
<div className="App">
</div>
);
}
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(
<React.StrictMode>
<App />
</React.StrictMode>
);
</script>
</body>
</html><React.StrictMode> решает проблемму? 
Средний
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