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import { useEffect, useRef } from "react";
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// A *ref* that is true after component mounts, then false once
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// the component unmounts.  This obviously must be a ref since
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// it makes no sense for unmounting or mounting to trigger
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// a render cycle!.  I made this up myself, but it does turn out
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// to be identical to an npm package to do this:
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//    https://github.com/jmlweb/isMounted/blob/master/index.js
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export default function useIsMounted() {
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  const is_mounted_ref = useRef<boolean>(false);
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  useEffect(() => {
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    is_mounted_ref.current = true;
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    return () => {
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      is_mounted_ref.current = false;
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    };
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  }, []);
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  return is_mounted_ref;
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}
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