Hot reload configuration

local.js

// Save the initial app so we can remove it from the server when
// there are Webpack Hot Module Reload updates.
let currentApp = initialApp
if (module.hot) {
  module.hot.accept('../index.js', () => {
    // Create a new Express app with the updated Cloud Function 
    // handlers.
    const newApp = setUpApp(require('../index.js'))
    
    // Remove the old Express app.   
    server.removeListener('request', currentApp)
    
    // Register the new app with the server.
    server.on('request', newApp)
    
    // Save the current app so we can remove it when there are 
    // updates.
    currentApp = newApp
  })
}