content: import React from 'react';
  import ReactDom from 'react-dom';
  import Header from '../components/header';
  import Main from '../components/main';
  import Footer from '../components/footer';
  
  class Index extends React.Component {
      render() {
          return (
              <div>
                  <Header></Header>
                  <Main></Main>
                  <Footer></Footer>
              </div>
          )
      }
  }
  
  ReactDom.render(
      <Index/>,
      document.getElementById('app')
  )