What is strict mode in React?

React.StrictMode is a useful component for highlighting potential problems in an application. Just like <Fragment>, <StrictMode> does not render any extra DOM elements. It activates additional checks and warnings for its descendants. These checks apply for development mode only.

import { StrictMode } from "react";

function App() {
return (
<Header />
<StrictMode>
<ComponentOne />
<ComponentTwo />
</StrictMode>
<Header />
);
}

In the example above, the strict mode checks apply to <ComponentOne> and <ComponentTwo> components only. i.e., Part of the application only.

Note: Frameworks such as NextJS has this flag enabled by default.