React js + redux

Counter.js

import  React ,{Component} from "react";
import { connect } from 'react-redux';

alert(connect)

class Counter extends Component{

    constructor(props){
        super(props);

        // this.state = {
        //     count : 0
        // }

        this.increment = this.increment.bind(this);
        this.decrement = this.decrement.bind(this);
    }

    increment(){
        this.props.dispatch({ type: 'INCREMENT' });

        // this.setState({
        //     count: this.state.count + 1
        // })
    }

    decrement(){
        this.props.dispatch({ type: 'DECREMENT' });
        // this.setState({
        //     count: this.state.count - 1
        // })
    }

    render(){

        return ( <div>
        <h2>Counter</h2>
        <div>
          <button onClick={this.decrement}>-</button>
          <span> {this.props.count}</span>
          <button onClick={this.increment}>+</button>
        </div>
         </div>
        )
    }


}

function mapStateToProps(state) {
    return {
      count: state.count
    };
  }

export  default  connect(mapStateToProps)(Counter);;

index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import Counter from './Counter';
import * as serviceWorker from './serviceWorker';
import { Provider } from 'react-redux';
import { createStore } from 'redux';


const initialState = {
    count: 0
};

function reducer(state = initialState, action) {

    //alert("actionType=>"+ action.type)

    switch(action.type) {
        case 'INCREMENT':
          return {
            count: state.count + 1
          };
        case 'DECREMENT':
          return {
            count: state.count - 1
          };
        default:
          return state;
      }
  }

const store = createStore(reducer);


  

const App = () => (
    <Provider store= {store}>
      <Counter/>
    </Provider>
  );

ReactDOM.render(<App />, document.getElementById('root'));

// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
// Learn more about service workers: http://bit.ly/CRA-PWA
serviceWorker.unregister();