old_contents: import React from 'react';
  import Demo from './demo';
  
  main();
  function main() {
  	let app;
  
  	if (process.env.NODE_ENV === 'development') {
  		app = document.createElement('div');
  		app.setAttribute('id', 'demo');
  		document.body.appendChild(app);
  	} else {
  		app = document.getElementById('demo');
  	}
  
  	React.render(<Demo />, app);
  }
  
new_contents: import React from 'react';
  import Demo from './demo';
  
  main();
  function main() {
  	let app;
  
  	app = document.createElement('div');
  	app.setAttribute('id', 'demo');
  	document.body.appendChild(app);
  
  	React.render(<Demo />, app);
  }
  
subject: simplify main function