React - Functional Component V/S Class Components

class ClassComponent extends React.Component {
 constructor(props) {
   super(props);
   this.state = {
     count: 0
   };
 }

 render() {
   return (
     <div>
       <p>count: {this.state.count} times</p>
       <button onClick={() => this.setState({ count: this.state.count + 1 })}>
         Click
       </button>
     </div>
   );
 }
}

Important
“The constructor for a React component is called before it is mounted. When implementing the constructor for a React.Component subclass, you should call super(props) before any other statement. Otherwise, this.props will be undefined in the constructor, which can lead to bugs.”