Cleanup memory leaks on an Unmounted Component in React Hooks

You could use the 'cancelActiveVisits' method of Inertia to cancel the active visit in useEffect cleanup hook.

So with this call the active visit will be cancelled and state will not get updated. 

useEffect(() => {
    return () => {
        Inertia.cancelActiveVisits(); //To cancel the active visit.
    }
}, []);

if the Inertia request get cancelled then it will return an empty response so you have to add an extra check to handle the empty response. Add add catch block as well to handle any potential errors.

 function handleSubmit(e) {
    e.preventDefault();
    setLoading(true);
    Inertia.post(window.route('login.attempt'), values)
      .then(data => {
         if(data) {
            setLoading(false);
         }
      })
      .catch( error => {
         console.log(error);
      });
  }

Alternate way (workaround)

You Could use useRef to hold the status of the component and based on this you can update the state.

Problem:

The warring is showing because the handleSubmit is trying to update the state of the component even though component has unmounted form the dom.

Solution:

Set a flag to hold the status of the component, if the component is mounted then the flag value will be true and if the component is unmounted the flag value will be false. So based on this we can update the state. For flag status we can use useRef to hold a reference.

useRef returns a mutable ref object whose .current property is initialized to the passed argument (initialValue). The returned object will persist for the full lifetime of the component. In useEffect return a function which will set the status of the component, if it is unmounted.

And then in useEffect in the cleanup function we can set the flag to false.

useEffecr cleanup function

The useEffect hook allows using a cleanup function. Anytime the effect is no longer valid, for example when a component using that effect is unmounting, this function is called to clean everything up. In our case, we can set the flag to false.

Example:

let _componentStatus.current =  useRef(true);
useEffect(() => {
    return () => {
        _componentStatus.current = false;
    }
}, []);

And in handleSubmit we can check if the component is mounted or not and update the state based on this.

function handleSubmit(e) {
    e.preventDefault();
    setLoading(true);
    Inertia.post(window.route('login.attempt'), values)
        .then(() => {
            if (_componentStatus.current) {
                setLoading(false);
            } else {
                _componentStatus = null;
            }
        })
}

In else set the _componentStatus to null to avoid any memory leaks.


Because it's the async promise call, so you must use a mutable reference variable (with useRef) to check already unmounted component for the next treatment of async response (avoiding memory leaks) :

Warning: Can't perform a React state update on an unmounted component.

Two React Hooks that you should use in this case : useRef and useEffect.

With useRef, for example, the mutable variable _isMounted is always pointed at the same reference in memory (not a local variable)

useRef is the go-to hook if mutable variable is needed. Unlike local variables, React makes sure same reference is returned during each render. If you want, it's the same with this.myVar in Class Component

Example :

const login = (props) => {
  const _isMounted = useRef(true); // Initial value _isMounted = true

  useEffect(() => {
    return () => { // ComponentWillUnmount in Class Component
        _isMounted.current = false;
    }
  }, []);

  function handleSubmit(e) {
    e.preventDefault();
    setLoading(true);
    ajaxCall = Inertia.post(window.route('login.attempt'), values)
        .then(() => {
            if (_isMounted.current) { // Check always mounted component
               // continue treatment of AJAX response... ;
            }
         )
  }
}

On the same occasion, let me explain you more information about React Hooks used here. Also, I will compare React Hooks in Functional Component (React >16.8) with the LifeCycle in Class Component.

useEffect : Most side-effects happen inside the hook. Examples of side effects are : data fetching, setting up a subscription, and manually changing the DOM React components. The useEffect replaces a lot of LifeCycles in Class Component (componentDidMount, componentDidUpate, componentWillUnmount)

 useEffect(fnc, [dependency1, dependency2, ...]); // dependencies array argument is optional

  1. Default behavior of useEffect runs both after the first render (like ComponentDidMount) and after every update render (like ComponentDidUpdate) if you don't have dependencies. It's like that : useEffect(fnc);

  2. Giving array of dependencies to useEffect will change its lifecycle. In this example : useEffect will be called once after the first render and every time count changes

    export default function () { const [count, setCount] = useState(0);

    useEffect(fnc, [count]);

    }

  3. useEffect will run only once after the first render (like ComponentDidMount) if you put an empty array for dependency. It's like that : useEffect(fnc, []);

  4. To prevent resource leaks, everything must be disposed when lifecycle of a hook ends (like ComponentWillUnmount). For example, with the empty array of dependency, the returned function will be called after component unmounts. It's like that :

    useEffect(() => { return fnc_cleanUp; // fnc_cleanUp will cancel all subscriptions and asynchronous tasks (ex. : clearInterval) }, []);

useRef : returns a mutable ref object whose .current property is initialized to the passed argument (initialValue). The returned object will persist for the full lifetime of the component.

Example : with the question above, we can't use a local variable here because it will be lost and re-initiated on each update render.

const login = (props) => {
  let _isMounted= true; // it isn't good because of a local variable, so the variable will be lost and re-defined on every update render

  useEffect(() => {
    return () => {
        _isMounted = false;  // not good
    }
  }, []);

  // ...
}

So, with combination of useRef and useEffect, we could completely cleanup memory leaks.

The good links that you could read more about the React Hooks are :

[EN] https://medium.com/@sdolidze/the-iceberg-of-react-hooks-af0b588f43fb

[FR] https://blog.soat.fr/2019/11/react-hooks-par-lexemple/


Before mutating the state, you should first check whether the component is still mounted.

As said above by @SanjiMika, when having an async action that causes this error, it means you are trying to mutate the component's state after it was un-mounted.

react-use provides hooks for that, you've got 2 options:

option #1: useMountedState

// check if isMounted before changing any state
const isMounted = useMountedState();

useEffect(() => {
  const asyncAction = executeAsyncAction();

  asyncAction.then(result => {
    if (isMounted) {
      // It's safe to mutate state here
    }
  });
}, []);

option #2: useUnmountPromise

/* `resolveWhileMounted` wraps your promise, and returns a promise that will resolve 
 * only while the component is still mounted */
const resolveWhileMounted = useUnmountPromise();

useEffect(async () => {
  const asyncAction = executeAsyncAction();

  resolveWhileMounted(asyncAction).then(result => {
    // It's safe to mutate state here
  });
}, []);

Tags:

Javascript

Promise

Reactjs

React Hooks

Inertiajs

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