Use useEffect right

useEffect.ts

// Fire useEffect only once on mount
cosnt executedRef = useRef(false);

useEffect(() => {
  if(executedRef.current) {
    return;
  }

  // doSomething();

  executedRef.current = true;
}, []);


// Fetch data
const Component: React.FC<T> = () => {
  const [data, setData] = useState(null);
  
  useEffect(() => {
    let cancelled = false;
    
    fetch('some/resource').then(data => {
      if(cancelled) {
        return;
      }
      
      setData(data);
    });
    
    return () => { cancelled = true };
  }, [])
  
  return // ..
};