useDebugValue

useDebugValue.md

The useDebugValue hook can be useful in advanced scenarios where you want to provide a custom string representation of a value for the React DevTools profiler. This can be useful for debugging and optimizing performance in complex applications.

For example, suppose you have a custom hook called useFormattedDate that returns the current date and time in a specific format. Here is an example of how this hook could be implemented:

function useFormattedDate() {
  const [date, setDate] = useState(new Date());

  useEffect(() => {
    const interval = setInterval(() => {
      setDate(new Date());
    }, 1000);

    return () => clearInterval(interval);
  }, []);

  return date.toLocaleString();
}

In this example, the useFormattedDate hook uses the useState and useEffect hooks to update the date and time every second. It returns the current date and time in a localized string representation.

If you want the React DevTools profiler to show a more readable representation of the value returned by this hook, you can use the useDebugValue hook to provide a custom string representation. Here is an example of how this could be done:

function useFormattedDate() {
  const [date, setDate] = useState(new Date());

  useEffect(() => {
    const interval = setInterval(() => {
      setDate(new Date());
    }, 1000);

    return () => clearInterval(interval);
  }, []);

  useDebugValue(date.toLocaleString());

  return date.toLocaleString();
}

In this example, the useDebugValue hook is used to provide a custom string representation of the value returned by the useFormattedDate hook. This custom representation will be displayed in the React DevTools profiler when the hook is used in a component, which can make it easier to understand and debug the behavior of the hook.

Note that the useDebugValue hook should only be used for debugging purposes, and should not be relied on for production code. It is intended to help developers understand the behavior of their code when using the React DevTools profiler, but it does not affect the behavior or performance of the code in any other way.