React-hooks. Can't perform a React state update on an unmounted component

The easiest solution is to use a local variable that keeps track of whether the component is mounted or not. This is a common pattern with the class based approach. Here is an example that implement it with hooks:

function Example() {
  const [text, setText] = React.useState("waiting...");

  React.useEffect(() => {
    let isCancelled = false;

    simulateSlowNetworkRequest().then(() => {
      if (!isCancelled) {
        setText("done!");
      }
    });

    return () => {
      isCancelled = true;
    };
  }, []);

  return <h2>{text}</h2>;
}

Here is an alternative with useRef (see below). Note that with a list of dependencies this solution won't work. The value of the ref will stay true after the first render. In that case the first solution is more appropriate.

function Example() {
  const isCancelled = React.useRef(false);
  const [text, setText] = React.useState("waiting...");

  React.useEffect(() => {
    fetch();

    return () => {
      isCancelled.current = true;
    };
  }, []);

  function fetch() {
    simulateSlowNetworkRequest().then(() => {
      if (!isCancelled.current) {
        setText("done!");
      }
    });
  }

  return <h2>{text}</h2>;
}

You can find more information about this pattern inside this article. Here is an issue inside the React project on GitHub that showcase this solution.

TL;DR

Here is a CodeSandBox example

The other answers work of course, I just wanted to share a solution I came up with. I built this hook that works just like React's useState, but will only setState if the component is mounted. I find it more elegant because you don't have to mess arround with an isMounted variable in your component !

Installation :

npm install use-state-if-mounted

Usage :

const [count, setCount] = useStateIfMounted(0);

You can find more advanced documentation on the npm page of the hook.

If you are fetching data from axios(using hooks) and the error still occurs, just wrap the setter inside the condition

let isRendered = useRef(false);
useEffect(() => {
    isRendered = true;
    axios
        .get("/sample/api")
        .then(res => {
            if (isRendered) {
                setState(res.data);
            }
            return null;
        })
        .catch(err => console.log(err));
    return () => {
        isRendered = false;
    };
}, []);