MEAN stack: Wondering api.js and crud.js

Question

I'm studying MEAN stack these day, So I make some sample apps following guidance. I made up "Bookshelf" application just few hours ago, this is provided by google cloud service, so I should delve into sample code to understand how it works.

Whole source code : https://github.com/GoogleCloudPlatform/nodejs-getting-started/tree/master/2-structured-data

Sample application : http://mymongo-1165.appspot.com/books

books/api.js

  router.get('/', function list(req, res) {
    model.list(10, req.query.pageToken,
      function(err, entities, cursor) {
        if (err) { return handleRpcError(err, res); }
        res.json({
          items: entities,
          nextPageToken: cursor
        });
      });
  });

books/curd.js

  router.get('/', function list(req, res) {
    model.list(10, req.query.pageToken,
      function(err, entities, cursor) {
        if (err) { return handleRpcError(err, res); }
        res.render('books/list.jade', {
          books: entities,
          nextPageToken: cursor
        });
      }
    );
  });

these 2 codes are similar, but I don't know why these similar codes comes up. I think crud.js enough, but why api.js comes up. Could you explain how these 2 codes work?

Answer 1

In this sample application, there are two interface:

1. graphic user interface (GUI) - curd.js handles generating HTML that is rendered later in the browser (in our case jade tempting language is involved)
2. application programming interface (API) - api.js provides the way to interact with application programmatically, without browser (ex: create new record in database, or query some data by making specific call to particular route)

For deeper understanding I would suggest learning more about express.js, that will give better idea what those outputs are.

P.S. Welcome to MEAN world :)