concept of componentdidmount and componentwillunmount in react js in function code example
Example 1: lifecycle method react
INITIALIZATION= setup props and state
MOUNTING= constructor->componentWillMount->render->componentDidMount//Birth
UPDATE= shouldComponentUpdate->componentWillUpdate->render
->componentDidUpdate //Growth
UNMOUNTING= componentWillUnmount //Death
Example 2: react lifecycle
constructor(props) {
super(props);
// Don't call this.setState() here!
this.state = { counter: 0 };
this.handleClick = this.handleClick.bind(this);
}