when to use jquery in react code example

Example 1: jquery in react

import React from 'react';
import ReactDOM from 'react-dom';
import $ from 'jquery';


//   react code here


$("button").click(function(){
    $.get("demo_test.asp", function(data, status){
        alert("Data: " + data + "\nStatus: " + status);
    });
});

// react code here

Example 2: react in jquery

class SomePlugin extends React.Component {
  componentDidMount() {
    this.$el = $(this.el);    this.$el.somePlugin();  }

  componentWillUnmount() {
    this.$el.somePlugin('destroy');  }

  render() {
    return <div ref={el => this.el = el} />;  }
}