Class component 
      import React, { useState } from 'react';

      class ClassComponent extends React.Component {
        constructor(props) {
          super(props);
          this.state = {
            likes: 0,
          };
          this.increment = this.increment.bind(this);
          this.decrement = this.decrement.bind(this);
        }

        increment() {
          this.setState({ likes: this.state.likes + 1 });
        }

        decrement() {
          this.setState({ likes: this.state.likes - 1 });
        }

        render() {
          return (
            <div>
              <>Likes <b>{this.state.likes}</b></>
              <button onClick={this.increment} style={btnCss}> +1 </button>
              <button onClick={this.decrement} style={btnCss}> -1 </button>
            </div>
          )
        }
      }

      <ClassComponent />
        Function component Function component is a modern way to write a component in react. 
      import React, { useState } from 'react';

      function FunctionComponent() {
        const [likes, setLikes] = useState(0);
        const increment = () => setLikes(likes + 1);
        const decrement = () => setLikes(likes - 1);

        return (
          <div>
            <div>Likes <b>{likes}</b></div>
            <button onClick={increment} style={btnCss}> +1 </button>
            <button onClick={decrement} style={btnCss}> -1 </button>
          </div>
        )
      }

      <FunctionComponent />
       