The Unmount Lifecycle

The unmount lifecycle lives outside of the main lifecycle, as it only comes into play when a component is removed from the DOM. This lifecycle is also far more limited, as the only lifecycle method it contains is componentWillUnmount().

componentWillUnmount()

componentWillUnmount() exists solely to perform and react to the component being removed from the DOM, and then is eventually removed entirely from existence. While it sounds a bit dramatic, it's important to note that this is what happens when a component is otherwise completely destroyed. It takes no arguments, and there are some caveats about using it.

The code for componentWillUnmount() might look something like this:

class App extends Component {
  componentWillUnmount() {
    alert("I've been removed!");
  }
  render() {
    return (<div className="App">Hello World!</div>);
 ...