Node Js - Web Apps using express

• Express.js is a web framework based on the core Node.js http module and Connect (http://www.senchalabs.org/
  connect/) components.\
• Express.js solves these and many other problems as abstraction and code organization. The framework
  provides a model-view-controller-like (MVC-like) structure for your web apps with a clear separation of concerns
  (views, routes, models)

•  Express.js Installation

          1.     express-generator: a global NPM package that provides the               command-line tool for rapid

app creation (scaffolding)
           2.     express: a local package module in your Node.js app’s node_modules folder

    To remove installed versions:

   $ sudo npm uninstall -g express-generator Or $ sudo npm uninstall -g express

    To Install express:

    $ npm install -g express-generator@4.0.0

• Local Express.js

 create folder named 'node-test'
$npm init  //this will create package.json file
$npm install express@4.1.2 --save  //this will add dependency in package.json

If we are adding dependency manually in package.json, run below command to install the added dependency.

$npm install

• Express.js Scaffolding(Creating skeleton)

           express [options] [dir|appname]

options

•     -e, --ejs: add EJS (http://embeddedjs.com/) engine support (by default, Jade
(http://jade-lang.com/tutorial/) is used)
•     -H, --hogan: add Hogan.js engine support
•     -c <engine>, --css <engine>: add stylesheet <engine> support, such as LESS
(http://lesscss.org/), Stylus (http://learnboost.github.io/stylus/) or Compass
(http://compass-style.org/) (by default, plain CSS is used)
•     -f, --force: force app generation on a nonempty directory

use below command to create skeleton:

express -c test express-test

To run the app(do $npm install if needed), use below:

DEBUG=my-application ./bin/ww

Go to browser and hit url http://localhost:3000/

Generated app.js file:

 

 var express = require('express');
var path = require('path');
var favicon = require('static-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var routes = require('./routes/index');
var users = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

app.use(favicon());
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded());
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', routes);
app.use('/users', users);

/// catch 404 and forwarding to error handler
app.use(function(req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});

/// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
    app.use(function(err, req, res, next) {
        res.status(err.status || 500);
        res.render('error', {
            message: err.message,
            error: err
        });
    });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
        message: err.message,
        error: {}
    });
});


module.exports = app;

• Details of generated app.js file

 app.use('/', routes);
app.use('/users', users);

These above syntax specify the routing with URL

 Query parameters in URL:

Express.js doesn’t allow developers to route by query string arguments, we need to write some middlewares as shown below:

app.use(function (req, res, next) {
if (req.query.id) {
// process the id, then call next() when done
else if (req.query.author) {
// same approach as with id
else if (req.query.id && req.query.ref) {
// process when id and ref present
} else {
next();
}
});

app.get('/about', function (req, res, next) {
// this code is executed after the query string middleware
});

Middleware as the Backbone of Express.js

app.use(favicon());
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded());
app.use(cookieParser()); 

For example, bodyParser() and cookieParser() add HTTP request payload
(req.body) and parsed cookie data (req.cookie), respectively. And in our app.js, app.use(logger('dev')); is
tirelessly printing in the terminal pretty logs for each request.

• Route helpers in express.js

•     all: catch every request (all methods)
•     get: catch GET requests
•     post: catch POST requests
•     put: catch PUT requests
•     del: catch DELETE requests

• Start to write simple  app 

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace$ mkdir nodejs_express
it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace$ cd nodejs_express/
it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ mkdir {public,public/css,public/img,public/js,db,views,views/includes,routes} it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ ls
db  public  routes  views
it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ npm init

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ ls
db  package.json  public  routes  views

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ sudo npm install express@4.1.2 --save


it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ sudo npm install jade@1.3.1 --save

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ sudo npm install mongoskin@1.4.1 --save

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ sudo npm install stylus@0.44.0 --save

folder structiure:

 

 app.js 

var express = require('express');
var http = require('http');
var path = require('path');

var app = express();

app.set('port', process.env.PORT || 3000);
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

app.all('*', function(req, res) {
res.render('index',{msg: 'Welcome to the Practical Node.js!'});
});

http.createServer(app).listen(app.get('port'),function(){
console.log('Express.js server listening on port ' +app.get('port'));
});


index.jade 
h1 hello
p Welcome to the Node.js!

Run below from terminal

it000483@IND-PUN-LAP-183:~/vuclip/eclipse-workspace/nodejs_express$ node app
Express.js server listening on port 3000