The useEffect Hook

The useEffect hook runs code after the component renders. It is used for side effects, such as updating the document title or starting a timer.

The second argument is a dependency array. The effect runs again whenever a value in that array changes.

• Empty array means the effect runs once after the first render
• Listing values means it reruns when any of them change
• Return a function to clean up, such as clearing a timer

React.useEffect(() => {
  document.title = "Hello";
}, []);