Reactjs - useEffect

Armands — Mon, 02 Dec 2019 14:05:50 +0000

Hi, I have some questions about reactjs useEffect hook.

if in my function component I write something like this:

const [myValue, setMyValue] = useState("initialValue");
useEffect(() => { console.log("Call this one time"); }, []);
useEffect(() => { console.log("Call when data changed"); }, [myValue]);

When I render component for first time I get both console logs. But WHY? When I pass empty array react knows that it should execute this callback once. Why it checks passed array values in initial rendering? Now it is not possible to execute second effect only when data has changed...

DEV Community: Armands

Reactjs - useEffect