Building your first Node app with Connect & Express

Building your first Node app with Connect & Express Christian Joudrey - @cjoudrey

Getting Started
Node.js: http://nodejs.org/#download
npm, a package manager for Node: curl http://npmjs.org/install.sh | sh
Use npm to install Connect and Express for Node: npm install connect && npm install express
Many more modules at: http://npm.mape.me/

Hello World in Node.js
// Load the http module
var http = require(' http ');
// Setup a HTTP server, listen on port 8080
http.createServer(function (req, res) {
res.writeHead(200, {
' Content-Type ': ' text/plain '
});
res.end(' Hello World ');
}).listen(8080, ' 127.0.0.1 ');

Node's HTTP module
Very low level.
No cookie handling or parsing.
No session support built-in.
No routing built-in.
No static file serving.

Connect makes it easier
Static File Server
Body Decoder
Cookie Decoder
Session Provider
Request Router
Logs
Sass/Less Compiler
Virtual Host Router

...but, you decide what blocks you want.

Hello World in Connect
// Load the connect module
var connect = require(' connect ');
// Setup a HTTP server, listen on port 8080
connect.createServer(function (req, res) {
res.writeHead(200, {
' Content-Type ': ' text/plain '
});
res.end(' Hello World ');
}).listen(8080, ' 127.0.0.1 ');

.use() and next()
var s = connect.createServer();
s.use(function (req, res, next) {
// Send to next handler if url not /about
if (req.url != ' /about ') return next();
res.end(' About page ');
});
s.use(function (req, res, next) {
res.end(' Default page ');
});
s.listen(8080, ' 127.0.0.1 ');

Routing Middleware
s.use(connect.router(function(app) {
app.get(' /users ', function(req, res, next) {
res.end(' List users ');
});
app.post(' /users ', function(req, res, next) {
res.end(' Create a new user ');
});
app.get(' /user/:id ', function(req, res, next) {
if (!is_admin(req)) {
return next( new Error(' access denied '));
}
res.end(' Edit user ' + req.params.id);
});
}));
s.use(function(err, req, res, next) {
res.end(err.message);
});

Full example with Connect
var s = connect.createServer();
s.use(connect.logger());
s.use(connect.favicon(__dirname + ' /static/favicon.ico '));
s.use(connect.static(__dirname + ' /static '));
s.use(connect.cookieParser()); // adds req.cookies
s.use(connect.bodyParser()); // adds req.body
s.use(connect.router(require(' ./users '));
s.use(connect.router(require(' ./index '));
s.use(function(err, req, res, next) {
res.end(' Internal Server Error ');
});
s.listen(8080, ' 127.0.0.1 ');

Express is even easier
Connect is easier than raw node.js, but still low level.
...but, it's good for simple RESTful API's
...or to make your own framework.
Express is a simple framework inspired by Sinatra (Ruby).
It's built on top of Connect.

Hello World in Express
var express = require(' express ');
var app = express.createServer();
app.get(' / ', function(req, res) {
res.send(' hello world ');
});
app.listen(8080);

Getting Started with Express
Generate skeleton apps: express –help
Generate app with sessions and template engine: express --sessions --template ejs hello
Generated structure: $ ls hello/ app.js logs pids public test views $ ls hello/views/ index.ejs layout.ejs

Configurations
app.configure(function() {
// Global configurations
app.use(express.bodyParser()); // parse incoming data
app.use(express.cookieParser()); // parse cookies
app.use(express.session({ secret: ' your secret ' });
});
app.configure(' development ', function() {
// Development configurations
// i.e. Error handler to print errors and show stack?
});
app.configure(' production ', function() {
// Production configurations
});
Controlled by: NODE_ENV=production node app.js

Routing
app.get(' /users ', function(req, res) {
// List user
});
app.post(' /users ', function(req, res) {
// Create user
// req.body contains POST data
});
app.get(' /user/:id ', function(req, res) {
// Edit user
// req.params.id contains value of :id param
});

Sanitizing Route Params
app.param(' :id ', function(v) {
return parseInt(v, 10);
});
res.send(' user id: ' + req.params.id);
});

Even better...
var integer = function(v) {
return parseInt(v, 10);
};
app.param(' :id ', integer);
res.send(' user id: ' + req.params.id);
});

Route Param Pre-conditions
var id = req.params.id;
User.get(id, function(err, user) {
if (err) return next(err);
res.send(' user ' + user.name);
});
});
app.put(' /user/:id ', function(req, res) {
var id = req.params.userId;
user.update(req.body);
});
});
Same logic every time there is :id

Even better...
var loadUser = function(req, res, next) {
var id = req.params.id;
if (!user) return next( new Error(' invalid userId '));
req.user = user;
next();
});
});
app.get(' /user/:id ', loadUser, function(req, res) {
res.send(' user ' + req.user.name);
});
app.put(' /user/:id ', loadUser, function(req, res) {
req.user.update(req.body);
});

You can stack them...
app.put(' /user/:id ', isAdmin, loadUser, function(req, res) {
});
app.put(' /user/:id ', function(req, res, next) {
// Verify if the current user is an admin
isAdmin(req, res, function(err) {
loadUser(req, res, function(err, user) {
});
});
});
...cleaner than...

Views
"Built-in" support for :
Jade (Haml-like): http://jade-lang.com/
EJS (Embedded JS): http://embeddedjs.com/
Support for partials.

Rendering Views
app.get(' /user/:id ', loadUser, function(req, res) {
res.render(' user_edit ', {
locals: {
user: req.user,
title: ' Edit User ' + req.user.username
}
});
});

Other useful functions...
app.helpers(Object)
Set functions that are available in your views
app.dynamicHelpers(Object)
Set helpers that require the req and res objects
app.error(Function), called when:
throw new Error()
next(new Error())

Interesting Links
Lots of Express examples: http://bit.ly/ExpressExamples
Express Documentation: http://bit.ly/ExpressDocs
Database wrappers and ORMs:
Mongoose (MongoDB, ORM-like): https://github.com/LearnBoost/mongoose
Cradle (CouchDB, HTTP wrapper): https://github.com/cloudhead/cradle
Couch-ar (CouchDB, Active Record implementation): https://github.com/scottburch/couch-ar

Questions? :)

Building your first Node app with Connect & Express

by Christian Joudrey on Apr 13, 2011

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