how use effect works reactjs code example

Example 1: react use effect

useEffect(() => {
	
  },[]);

Example 2: useeffect react

useEffect(() => {
  window.addEventListener('mousemove', () => {});

  // returned function will be called on component unmount 
  return () => {
    window.removeEventListener('mousemove', () => {})
  }
}, [])