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ReactIntermediate#hooks
ReactIntermediate#hooks#effects
Explain useEffect and its dependency array.
useEffect runs side effects after render. With no array it runs after every render, with [] only after mount, and with dependencies whenever one of them changes. The returned function cleans up before the next run and on unmount.
Example
useEffect(() => {
const id = setInterval(tick, 1000);
return () => clearInterval(id);
}, []);