React Hooks Exhaustive-deps async infinite Loop

Question

I have the following component:

import React, { useState, useEffect } from "react";

const App = () => {
    const [data, setData] = useState<null | any[]>(null);
    const [checked, setChecked] = useState(false);
    const [loading, setLoading] = useState(false);

    useEffect(() => {
        setLoading(true);

        (async () => {
            if (data) {
                // Could do something else here if data already exsisted
                console.log("Data exists already");
            }

            const ret = await fetch("https://jsonplaceholder.typicode.com/users?delay=1000", { cache: "no-store" });
            const json = await ret.json();
            setData(json);
            setLoading(false);
        })();

    }, [checked]);

    return (
        <>
            <h1>useEffect Testing {loading && " ⌛"}</h1>
            <hr />
            <input type="checkbox" checked={checked} onChange={(e) => setChecked(e.target.checked)} />
            <pre style={{ fontSize: "0.8em" }}>{JSON.stringify(data)}</pre>
        </>
    );
};

export default App;

Currently, my if(data) is pointless however if I wanted to check the current data state and then run an asynchronous function based on the state the eslint(react-hooks/exhaustive-deps) tells me the hook is missing the data dependency, which it is. The problem comes when I add data to the dependency list causing an infinite loop.

Any idea how to resolve this? It feels like it should be fairly simple pattern however everything I find recomends using the extended setState(prev => prev + 1) overload which doesn't help me in this case.

Answer 1

You are setting data and also reading it in the effect. This will cause you an infinite loop unless you manually stop it. Here are a few solutions.

Return if there is data instead of modify it:

useEffect(() => {
    setLoading(true);

    (async () => {
        if (data) {
            // Could do something else here if data already exsisted
            console.log("Data exists already");
            return;
        }

        const ret = await fetch("https://jsonplaceholder.typicode.com/users?delay=1000", { cache: "no-store" });
        const json = await ret.json();
        setData(json);
        setLoading(false);
    })();

}, [checked, data]);

Remove your reliance on data in the effect that sets it (what I'd do):

useEffect(() => {
    setLoading(true);

    (async () => {
        const ret = await fetch("https://jsonplaceholder.typicode.com/users?delay=1000", { cache: "no-store" });
        const json = await ret.json();
        setData(json);
        setLoading(false);
    })();

}, [checked]);

useEffect(() => {
        if (data) {
            // Could do something else here if data already exsisted
            console.log("Data changed and exists!");
        }
}, [data]);

Or you can manually do something that stops the infinite loop.

useEffect(() => {
    if (loading || data) {
      console.log('Do something with loading or data, but do not modify it!')
      return;
    }

    setLoading(true);

    (async () => {
        const ret = await fetch("https://jsonplaceholder.typicode.com/users?delay=1000", { cache: "no-store" });
        const json = await ret.json();
        setData(json);
        setLoading(false);
    })();
}, [checked, data]);