The site is rendered at build time, then 'rehydrated' when the javascript bundle loads on the client machine.

Build process:

1. React app is rendered to a string at build time, passing env=node as a prop. This string is passed into a mustache template.

2. SCSS and js are compiled, concatenated and minified.

What happens when the page is loaded?

1. First, a static version of the site is delivered in plain HTML which is seen by the user until 'bundle.js' loads. The state used for the App is DEFAULT_STATE.

2. When 'bundle.js' has been loaded, parsed and executed, the React app is rendered again. If there are no changes to be made then the DOM is not touched (except for the attachment of event listeners). In our case, since the static version does not contain any of the 'item cards', these will be rendered but the heading etc will not be.

3. Initially, the app is rendered using DEFAULT_STATE (the same state used on the server). Then, once the App component has mounted, the state is updated (inside componentDidMount()) with the client side state.

   We use DEFAULT_STATE initially so that the render tree can be updated efficiently via setState. If the client state was used straight away, the whole tree would have to be discarded and re-rendered.