wp-calypso/client/server/README.md

Server-side Rendering

Output is built on the server side by the following modules (corresponding to subdirectories of server/):

• boot is the entry point, which loads the Express middleware and configures some basic settings. It then invokes
• pages, which uses Express to
  • set up even more configuration, depending the type of the environment (development, staging, production, etc.), settings from /config, etc.
  • define the basic routing, depending on whether the user is logged in or not
  • compute necessary variables, wraps them in a context object
  • render content by passing that to 404.jsx, 500.jsx, browsehappy.jsx, support-user.jsx, index.jsx or desktop.jsx template files, respectively.
• index.jsx
  • builds an HTML skeleton, including <script> tags to load relevant JavaScript files (minified unless in debug mode or in the development environment) that contain client-side (React) rendering code