React 18 strict mode causing component to render twice

user_17171424 0
Viewed 3792

The changes to strict-mode in React version 18 causes my code to render twice, which causes an error in axios abort controller, but I don't know how to clear the error from the browser console after the app renders twice.

Please note: I am working on a sign-up / log-in app and even after I successfully logged in, React takes me back to the log-in page, because of the axios error

useEffect(() => {
        let isMounted = true;
        // used by axios to cancel request
        const controller = new AbortController();

        const getGoals = async () => {
            try {
                const response = await goalPrivate.get("/goals", {
                    // option to cancel request
                    signal: controller.signal
                })
                console.log(response?.data);
                // set goals state when component mounts
                isMounted && setGoals(response?.data);
            } catch (error) {
                console.log(error.message);
                // when refreshToken expires
                navigate("/login", { state: { from: location }, replace: true });
            }
        }

        getGoals();

        // cleanup function
        return () => {
            // don't set state if component unmounts
            isMounted = false;
            // cancel request if component unmounts
            controller.abort();
        }
        
        // eslint-disable-next-line react-hooks/exhaustive-deps
    }, [])

shows code containing useEffect and it's side effect

strict-mode reactjs development-environment javascript
5 Answers

React StrictMode calls all Effects twice to make sure their cleanup/unmount handlers work as intended. You may need to change your effects accordingly, even if they have an empty dependency list and would normally not unmount before the site is closed.

Note, this only happens in Strict + development mode. In a production build, effects will only be called once and when their dependencies change.

Fore more context, see https://reactjs.org/docs/strict-mode.html#ensuring-reusable-state

user_115724980

Had the same problem and fixed it this way.

When the abortController is aborted you jump to the catch so you just check if the signal is aborted or not to execute the rest of your code.

useEffect(() => {
    const abortController = new AbortController();

    fetch("https://pokeapi.co/api/v2/pokemon", {
      signal: abortController.signal,
    })
      .then((res) => res.json())
      .then(console.log)
      .catch((err) => {
        if (abortController.signal.aborted) return;
        console.log(err);
        // Your navigate
      });

    return () => {
      abortController.abort();
    };
  }, []);
user_146147280

You should classify the error response depends on error code or http status code.

Eg:

...
try {
    // Create axios request
} catch (e: AxiosError) {
    if (error.code === 'ERR_CANCELED') {
        // When abort controller executed
    } else (error.response.status == 401) {
        // When you get http code 401 (Un-authenticated)
        // Eg:
        navigate("/login", { state: { from: location }, replace: true });
    } else {
        // Etc...
    }
}
...
user_46680270

If you have the StrictMode enabled, it will fire two times the useEffect on development mode to make sure that you are aware of the possible side-effects that could appear.

user_192637450

React 18 now has Strict.Mode mount, unmount, and remount components which causes the abortController to issue an error on the first unmount. Remember, this only happens in development mode when Strict.Mode is applied in your index.js. We can check for that behaviour while in development-mode.

try {
     // fetch API data
  } catch (error) {
       if (process.env.NODE_ENV === "development" && error) {
         // ignore the error
        console.log(error.message);
   } else {
     // when refreshToken expires, go back to login
    navigate("/login", { state: { from: location }, replace: true });
  }
}
user_171714240
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