reactjs - To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function

Question

I have this code

import ReactDOM from "react-dom";
import React, { useState, useEffect } from "react";
import { BrowserRouter as Router, Route, Link } from "react-router-dom";

function ParamsExample() {
  return (
    <Router>
      <div>
        <h2>Accounts</h2>
        <Link to="/">Netflix</Link>
        <Route path="/" component={Miliko} />
      </div>
    </Router>
  );
}

const Miliko = ({ match }) => {
  const [data, setData] = useState([]);
  const [isLoading, setIsLoading] = useState(false);
  const [isError, setIsError] = useState(false);

  useEffect(() => {
    (async function() {
      setIsError(false);
      setIsLoading(true);
      try {
        const Res = await fetch("https://foo0022.firebaseio.com/New.json");
        const ResObj = await Res.json();
        const ResArr = await Object.values(ResObj).flat();
        setData(ResArr);
      } catch (error) {
        setIsError(true);
      }
      setIsLoading(false);
    })();
    console.log(data);
  }, [match]);
  return <div>{`${isLoading}${isError}`}</div>;
};

function App() {
  return (
    <div className="App">
      <ParamsExample />
    </div>
  );
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

I created three links that open the Miliko component. but when I quickly click on the links I get this error:

To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.

Answer 1

I think the problem is caused by dismount before async call finished.

const useAsync = () => {
  const [data, setData] = useState(null)
  const mountedRef = useRef(true)

  const execute = useCallback(() => {
    setLoading(true)
    return asyncFunc()
      .then(res => {
        if (!mountedRef.current) return null
        setData(res)
        return res
      })
  }, [])

  useEffect(() => {
    return () => { 
      mountedRef.current = false
    }
  }, [])
}

mountedRef is used here to indicate if the component is still mounted. And if so, continue the async call to update component state, otherwise, skip them.

This should be the main reason to not end up with a memory leak (access cleanedup memory) issue.

Update

The above answer leads to the following component that we use inside our team.

/**
 * A hook to fetch async data.
 * @class useAsync
 * @borrows useAsyncObject
 * @param {object} _                props
 * @param {async} _.asyncFunc         Promise like async function
 * @param {bool} _.immediate=false    Invoke the function immediately
 * @param {object} _.funcParams       Function initial parameters
 * @param {object} _.initialData      Initial data
 * @returns {useAsyncObject}        Async object
 * @example
 *   const { execute, loading, data, error } = useAync({
 *    asyncFunc: async () => { return 'data' },
 *    immediate: false,
 *    funcParams: { data: '1' },
 *    initialData: 'Hello'
 *  })
 */
const useAsync = (props = initialProps) => {
  const {
    asyncFunc, immediate, funcParams, initialData
  } = {
    ...initialProps,
    ...props
  }
  const [loading, setLoading] = useState(immediate)
  const [data, setData] = useState(initialData)
  const [error, setError] = useState(null)
  const mountedRef = useRef(true)

  const execute = useCallback(params => {
    setLoading(true)
    return asyncFunc({ ...funcParams, ...params })
      .then(res => {
        if (!mountedRef.current) return null
        setData(res)
        setError(null)
        setLoading(false)
        return res
      })
      .catch(err => {
        if (!mountedRef.current) return null
        setError(err)
        setLoading(false)
        throw err
      })
  }, [asyncFunc, funcParams])

  useEffect(() => {
    if (immediate) {
      execute(funcParams)
    }
    return () => {
      mountedRef.current = false
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [])

  return {
    execute,
    loading,
    data,
    error
  }
}