score:138

Accepted answer

Since the cleanup is not dependent on the username, you could put the cleanup in a separate useEffect that is given an empty array as second argument.

Example

const { useState, useEffect } = React;

const ForExample = () => {
  const [name, setName] = useState("");
  const [username, setUsername] = useState("");

  useEffect(
    () => {
      console.log("effect");
    },
    [username]
  );

  useEffect(() => {
    return () => {
      console.log("cleaned up");
    };
  }, []);

  const handleName = e => {
    const { value } = e.target;

    setName(value);
  };

  const handleUsername = e => {
    const { value } = e.target;

    setUsername(value);
  };

  return (
    <div>
      <div>
        <input value={name} onChange={handleName} />
        <input value={username} onChange={handleUsername} />
      </div>
      <div>
        <div>
          <span>{name}</span>
        </div>
        <div>
          <span>{username}</span>
        </div>
      </div>
    </div>
  );
};

function App() {
  const [shouldRender, setShouldRender] = useState(true);

  useEffect(() => {
    setTimeout(() => {
      setShouldRender(false);
    }, 5000);
  }, []);

  return shouldRender ? <ForExample /> : null;
}

ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>

<div id="root"></div>

score:0

useEffect are isolated within its own scope and gets rendered accordingly. Image from https://reactjs.org/docs/hooks-custom.html

enter image description here

score:0

Here is my solution, generalized into a custom hook:

import React, { useEffect, useRef } from 'react';

const useUnmountEffect = (effect, dependencies) => {
  if (typeof effect !== 'function') {
    console.error('Effect must be a function');
  }

  const componentWillUnmount = useRef(false)

  useEffect(() => () => {
    componentWillUnmount.current = true
  }, []);

  useEffect(() => () => {
    if (componentWillUnmount.current) {
      effect?.();
    }
  }, dependencies);
}

export default useUnmountEffect;

score:0

what about:

function useOnUnmount(callback: () => void) {
    const onUnmount = useRef<(() => void) | null>(null);
    onUnmount.current = callback;

    useEffect(() => {
        return () => onUnmount.current?.();
    }, []);
}

useOnUnmount(() => {
    console.log("unmount", props);
});

score:2

function LegoComponent() {

  const [lego, setLegos] = React.useState([])

  React.useEffect(() => {
    let isSubscribed = true
    fetchLegos().then( legos=> {
      if (isSubscribed) {
        setLegos(legos)
      }
    })
    return () => isSubscribed = false
  }, []);

  return (
    <ul>
    {legos.map(lego=> <li>{lego}</li>)}
    </ul>
  )
}

In the code above, the fetchLegos function returns a promise. We can “cancel” the promise by having a conditional in the scope of useEffect, preventing the app from setting state after the component has unmounted.

Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.

score:2

instead of creating too many complicated functions and methods what I do is I create an event listener and automatically have mount and unmount done for me without having to worry about doing it manually. Here is an example.

//componentDidMount
useEffect( () => {

    window.addEventListener("load",  pageLoad);

    //component will unmount
    return () => {
       
        window.removeEventListener("load", pageLoad);
    }

 });

now that this part is done I just run anything I want from the pageLoad function like this.

const pageLoad = () =>{
console.log(I was mounted and unmounted automatically :D)}

score:3

Using custom js events you can emulate unmounting a componentWillUnmount even when having dependency.

Problem:

    useEffect(() => {
    //Dependent Code
    return () => {
        // Desired to perform action on unmount only 'componentWillUnmount' 
        // But it does not
        if(somethingChanged){
            // Perform an Action only if something changed
        }
    }
},[somethingChanged]);

Solution:

// Rewrite this code  to arrange emulate this behaviour

// Decoupling using events
useEffect( () => {
    return () => {
        // Executed only when component unmounts,
        let e = new Event("componentUnmount");
        document.dispatchEvent(e);
    }
}, []);

useEffect( () => {
    function doOnUnmount(){
        if(somethingChanged){
            // Perform an Action only if something changed
        }
    }

    document.addEventListener("componentUnmount",doOnUnmount);
    return () => {
        // This is done whenever value of somethingChanged changes
        document.removeEventListener("componentUnmount",doOnUnmount);
    }

}, [somethingChanged])

Caveats: useEffects have to be in order, useEffect with no dependency have to be written before, this is to avoid the event being called after its removed.

score:20

To add to the accepted answer, I had a similar issue and solved it using a similar approach with the contrived example below. In this case I needed to log some parameters on componentWillUnmount and as described in the original question I didn't want it to log every time the params changed.

const componentWillUnmount = useRef(false)

// This is componentWillUnmount
useEffect(() => {
    return () => {
        componentWillUnmount.current = true
    }
}, [])

useEffect(() => {
    return () => {
        // This line only evaluates to true after the componentWillUnmount happens 
        if (componentWillUnmount.current) {
            console.log(params)
        }
    }

}, [params]) // This dependency guarantees that when the componentWillUnmount fires it will log the latest params

score:203

You can use more than one useEffect().

For example, if my variable is data1, I can use all of this in my component:

useEffect( () => console.log("mount"), [] );
useEffect( () => console.log("data1 update"), [ data1 ] );
useEffect( () => console.log("any update") );
useEffect( () => () => console.log("data1 update or unmount"), [ data1 ] );
useEffect( () => () => console.log("unmount"), [] );

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