ComponentDidMount called twice - reactjs

Question

ComponentDidMount in my overarching App component is being called twice, and I can't figure out why. So far google suggests this is usually due to a lack of keys that means the app has to assume things have changed and delete everything instead of just the relevant portion of the DOM, but I stripped my app as bare as I can get reasonably get it and it's still happening.
index.tsx:
import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import 'bootstrap/dist/css/bootstrap.min.css';
import App from './App';
import reportWebVitals from './reportWebVitals';
const root = ReactDOM.createRoot(
document.getElementById('root') as HTMLElement
);
root.render(
<React.StrictMode>
<App global={{baseUrl: "http://localhost", port: 54887}} />
</React.StrictMode>
);
// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
reportWebVitals();
App.tsx:
import React from 'react'
import CurrentItems, { CurrentItemsProps } from './CurrentItems';
import Navigation, { NavigationProps } from './Navigation';
import { CombinedNavigationProps } from './Navigation';
import './App.css';
import { GlobalProps } from './GlobalProps';
interface AppProps extends GlobalProps {}
interface AppState {
navigation: NavigationProps;
}
class App extends React.Component<AppProps, AppState> {
constructor(props: AppProps){
super(props);
//this.onSelectedViewChange = this.onSelectedViewChange.bind(this);
}
componentDidMount(){
console.log("app did mount");
}
onSelectedViewChange(view: string) {
}
render(){
if(this.state === undefined || this.state === null){
return (<div>Loading...</div>);
} else {
return (
<div>
Loaded.
</div>
);
}
}
}
export default App;
Link to github for full code
Screenshot of console output:

Answer 1

Per #NicholasTower's comment, it's because I'm using strict mode. Seems like it's time to learn about Hooks! Guess I didn't go far enough in the ReactJS introduction documentation.