Use useLayoutEffect if the side effect that you are performing makes an observable change to the DOM that will require the browser to paint that update you've made.
Otherwise, use useEffect
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For some more context, componentDidMount would render twice before painting once, in order to stop a flicker in the browser if the DOM changes. useEffect also runs after mount, but it runs after the first paint. useLayoutEffect can help stop a flicker when setting state synchronously.