Node JS, Express Structure and Require Confusion

Question

This has been driving me crazy. I'm new to NodeJS. I love it so far but some things have been throwing me off. I was handed a very basic starting point to a node project and I'm unsure how to search google for this.

//myapp/server.js

var config  = require('./config');
var app     = express();
var api     = require('./app/routes/api')(app, express); // <-- this?

app.use('/', api);

var server = app.listen(3000, function () {
    console.log('\n============================');
    console.log(' Server Running on Port 3000  ');
    console.log('============================\n');
});

Then there's the api.js file that contains the routes.

//myapp/app/routes/api.js

var config   = require('../../config');
var mysql    = require('mysql');

module.exports = function(app, express) {

    var api = express.Router();

    api.all('/', function(req, res) {...});

    api.all('/route-two', function(req, res) {...});

    api.all('/another-route', function(req, res) {...});

    return api;
}

Ideally I'd like to break up what's going on here into a more organized structure but, I want to understand what I'm doing exactly.

The main thing that is confusing me is this line

var api = require('./app/routes/api')(app, express);

I was unaware that you can have ()() next to each other without a . or something joining them. Can someone explain what is happening?

Also what is the point of (app, express)? It appears that app and express are getting passed to the api part of the application so it's scope can be reached? Am I way off?

If there is a cleaner approach to this I would love to get some insight. I appreciate any thoughts.

Thanks!

---

EDIT To make sure I am understanding...

var api = require('require this file')(params available to this file);

Moving any requires from api.js to server.js then include those as parameters

var api = require('./app/routes/api')(config, app, express, mysql);

---

EDIT

After more helpful feedback from @AhmadAssaf @Gurbakhshish Singh and @guy mograbi

Modules I want to use in another file other than where they are require()ed should be passed in through the second set of ()

//.server.js
var config = require('./config');
var app    = express();                                          
var api    = require('./app/routes/api')(config, app, express); 
                                           |      |        |
                              _____________/______/________/
                             /      /      /
//.app/routes/api.js         |      |      |
module.exports = function(config, app, express) {

    var api = express.Router();

    // code to handle routes
}

Could be wrong with this part but based on what I think I am understanding.

//.server.js
var config = require('./config');
var app    = express();

var register = require('./app/routes/register')(config, app, express); 
var login    = require('./app/routes/login')(config, app, express); 
                                               |      |        |
                              _________________/______/________/
                             /      /      /
//.app/routes/login.js      |      |      |
module.exports = function(config, app, express) {...handle login...}

//.app/routes/register.js    
module.exports = function(config, app, express) {...handle registration...}    

etc. etc.

Hopefully my thinking is about right. I appreciate everyones help on this! :)

Answer 1

So basically you have to understand few thing

• module.exports wraps a Javascript object and export it to be used as a pluggable piece of code around a node.js application
• The wrapped javascript object can be a JSON object, Javascript variable, function, etc.

What you have up there in the api module is a function that takes two parameters. When you require that module you want to pass some constructors to that function and thats the use of the second () after the module name in the first ()

requiring express once in your program and passing the variable around is more or less a singleton pattern. What you can also do is pass the config object as well to the api module instead of requiring it again :)