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VisualizaçõesuseEffect fetch request is pulling data twice
What I Want:
I'm pulling data from an api, then setting the data to state. I've done this inside a useEffect hook, but when I console.log the data afterwards, it's displaying the data twice, sometimes 4 times. I'm at a loss as to why this is happening.
What I've Tried:
console.logwithin useEffect to see data from source- disabling react developer tools within chrome.
My Code:
// make api call, assign response to data state
const [apiData, setApiData] = useState();
useEffect(() => {
async function fetchData() {
try {
await fetch('https://restcountries.com/v3.1/all')
.then(response => response.json())
.then(data => setApiData(data));
} catch (e) {
console.error('Error fetching api data', e);
};
};
fetchData();
}, []);
console.log(apiData);
Result of console.log:
2 Respostas
Responde à pergunta0
If you are using React version 18+, StrictMode has a behavior change. Before it wasn't running effects twice, now it does to check for bugs. ( Actually, it does mount-remount, which causes initial render effects to fire twice)
https://reactjs.org/blog/2022/03/29/react-v18.html#new-strict-mode-behaviors
0
As was mentioned in the other comment this is due to effects being "double invoked" in strict-mode.
A common solution and one I believe has been suggested by the React team (although am struggling to find where I read this) is to use useRef.
// make api call, assign response to data state
const [apiData, setApiData] = useState();
const hasFetchedData = useRef(false);
useEffect(() => {
async function fetchData() {
try {
await fetch('https://restcountries.com/v3.1/all')
.then(response => response.json())
.then(data => setApiData(data));
} catch (e) {
console.error('Error fetching api data', e);
};
};
if (hasFetchedData.current === false) {
fetchData();
hasFetchedData.current = true;
}
}, []);