How does control flow from app.start() in MeanJS framework

Question

I am trying to play around with the MEAN framework. I used their scaffolding available here . But I am getting confused on how the control flow happens from the time we start the server.js [ node server.js ] file.

Adding snippets of some files, the entire code is here

./server.js

var app = require('./config/lib/app');
var server = app.start();

./config/lib/app.js

module.exports.start = function start(callback) {
  var _this = this;

  _this.init(function (app, db, config) {

    // Start the app by listening on <port> at <host>
    app.listen(config.port, config.host, function () {
      // Create server URL
      var server = (process.env.NODE_ENV === 'secure' ? 'https://' : 'http://') + config.host + ':' + config.port;
      // Logging initialization
      console.log('--');
      .....
      if (callback) callback(app, db, config);
    });
  });
};

For eg, where do the parameters come from in _this.init(function (app, db, config){ segment when im only calling app.start(); -

Answer 1

该function (app, db, config){...}在_this.init(function (app, db, config){...}只是函数声明 ，执行算不了什么 ，执行都是在这里完成（线26） if (callback) callback(app, db, config);其中传递的config参数是此处声明的全局变量var config = require('../config') （第6行）， app参数在此处声明var app = express.init(db); （第25行），而db参数是mongooseService.connect调用（第20行）的结果（数据库实例）。