Slides from my Super Mondays talk giving a brief introduction to Node.js

1. Ian Oxley
Super Mondays, 26 Sept 2011

2. • Hi, I’m Ian
• Web / Application Developer at Sage
• http://ianoxley.com
• @ianoxley

3. What is Node?
“Node is a set of libraries for JavaScript that allows it to run
outside the browser. It is primarily focused on creating simple, easy
to build network clients and servers.”

4. • Event loop approach
• Easy and safe to build scalable
servers
• All I/O should be non-blocking
• Use asynchronous callbacks to handle
events

5. var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello Worldn');
}).listen(8124, "127.0.0.1");
console.log('Server running at http://
127.0.0.1:8124/');

7. Parallel I/O
• Node assumes all I/O has unbounded
latency
• 0 to infinity time
• Easy to do parallel I/O:
• Use events as placeholders
• Fire callbacks as events happen

8. Serial I/O
• Ordered serial I/O
• Each task completes before the next
one starts
• Nested callbacks
• Pyramid code - hard to understand
and maintain

9. // Nesting callbacks to produce serial requests
server.on('request', function(req, res) {
//get session information from memcached
memcached.getSession(req, function(session) {
//get information from db
db.get(session.user, function(userData) {
//some other web service call
ws.get(req, function(wsData) {
//render page
page = pageRender(req, session, userData, wsData);
//output the response
res.write(page);
});
});
});
});

10. // Using declared functions to seperate out code
var render = function(wsData) {
page = pageRender(req, session, userData, wsData);
};
var getWsInfo = function(userData) {
...
};
var getDbInfo = function(session) {
...
};
var getMemCached = function(req, res) {
...
};

12. Node events
• Potentially infinite based on what’s
happening on the server
• e.g. HTTP server module has a
“request” event

13. EventEmitter
• No DOM in Node so we have the
EventEmitter class
• Main two methods: on and emit
• Inherit from EventEmitter to attach it’s
methods to your class

14. var util = require('util'),
EventEmitter = require('events').EventEmitter;
var Server = function() {
console.log('init');
};
util.inherits(Server, EventEmitter);
var s = new Server();
s.on('wtf', function() {
console.log('wtf');
});
s.emit('wtf');

15. Modules
• Node uses CommonJS module system:
http://www.commonjs.org/
• One module per file approach e.g. the
file foo.js contains the foo module
• Add functions and variables to the
exports object - everything else is

16. // circle.js
var PI = Math.PI;
exports.area = function (r) {
return PI * r * r;
};
exports.circumference = function (r) {
return 2 * PI * r;
};

18. Where to get Node
• Official site: http://nodejs.org
• Download:
• Source code for OS X / Linux
• .exe for Windows
• Wiki: https://github.com/joyent/node/wiki

19. ?