useEffect(() => {
    //will be called on every load
})

useEffect(() => {
    //will be called on component mount
  window.addEventListener('mousemove', () => {});

  // returned function will be called on component unmount 
  return () => {
    window.removeEventListener('mousemove', () => {})
  }
}, []) // <---- empty array at end will cause to only run on first load