useeffect in function component code example

Example 1: useeffect react

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

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

Example 2: how to have a function inside useeffect

useEffect(() => {
  fetch(`https://jsonplaceholder.typicode.com/${query}`)
    .then(response => response.json())
    .then(json => setData(json));
}, [query]); // only re-run on query change