Introduction to Node.js

Introduction to
Richard Lee
Taipei Google Technology User Group

console.info(me);
• Richard Lee

• iOS / Ruby / JavaScript developer

• Co-founder of Polydice, Inc.

• Email: dlackty@gmail.com

• Twitter: @dlackty

Node.js
• Event-driven I/O framework

• Usually known as server-side JavaScript

• Based on V8 JavaScript Engine by Google

• Great community supported

• However, only on Unix-like platforms

Event-driven I/O framework
• Everything in Node.js is asynchronous

• Doesn’t have to wait for slow ﬁle I/O or database
operations to continue processing

• Make it insanely fast

• Handle millions of concurrent connections at once

• It’s also known as non-blocking server

Benchmark 100 concurrent clients
1 megabyte response

Node.js

Nginx

Thin

Mongrel
req/sec

0 225 450 675 900

A synchronous example
data = readFromDatabase();
printData(data);

doSomethingUnrelated();

• The program get blocked when read from database

• Many CPU cycles are wasted

An asynchronous example
readFromDatabase(function(data) {
printData(data);
});


• doSomethingUnrelated() get called immediately

• printData(data) will be called when ﬁnish reading

• Everything runs in parallel

Benchmark II

Node.js User CPU System CPU

Python

Perl

PHP

0 22.5 45 67.5 90

http://blog.famzah.net/2010/07/01/cpp-vs-python-vs-perl-vs-php-
performance-benchmark/

What is not Node.js
• Node.js is not full stack Web framework

• No built-in MVC architecture

• No built-in database support

• No built-in URL routing system

• But all these thins can be found from modules

Event-loop basis
• All your codes run in an ”event-loop”

• Stop if no event listeners, and event emitters

• That is,

• a loop waits for event

• a loop run in single thread

• but everything else is asynchronous

EventEmitter
• EventEmitter is the core component for Node.js

• Anything related to I/O wrapped with it

• Your own class usually inherits it

Using EventEmitter
server.on('connection', function (stream) {
console.log('someone connected!');
});

server.once('connection', function (stream) {
console.log('Ah, we have our first user!');
});

Create your own emitter
var events = require('events');
var eventEmitter = new events.EventEmitter();

eventEmitter.on('someOccurence', function(message){
console.log(message);
});

eventEmitter.emit('someOccurence', 'Something
happened!');

Some pitfalls
• Remember that event-loop is single thread

• Always handle event efﬁciently, otherwise

• Event callbacks will get queued in order

• User response time becomes longer

• The connection won’t drop, though

Bad example
ee = new require('events').EventEmitter();

die = false;
ee.on('die', function() { die = true; });

setTimeout(function() { ee.emit('die'); }, 100);
while(!die);

console.log('done'); // never be called

Fix single thread issue
• Spawn new thread if needed

• The communication is also down by events

• Some principle to follow

• Use event callbacks

• Avoid share states variables

• I/O should be handled by built-in function calls

Good, so how?
• Coding in JavaScript are natively asynchronous

• Always need to writes callback functions for I/O

• Organize your codes as

• I/O components - In event-loop

• Computational components - Spawn workers

Thus, it’s quite common to see
doSomething(data, function(data) {
doAnotherThing(data, function(response) {
doYetAnotherThing(data, function() {
doJustYetAnotherThing(data, function()) {
// kinda of crazy
});
});
});
});


HTTP Server
• Node.js has built-in HTTP server library

• Low-level design instead of high level abstraction

• Supports HTTP 1.1

• Thus, the network connection will persist

HTTP Hello World example
var http = require('http');

http.createServer(function(request, response) {
response.writeHead(200, {'Content-Type': 'text/
plain'});
response.end('Hello Worldn');
}).listen(8124, "127.0.0.1");

console.log('Server running at http://
127.0.0.1:8124/'

HTTP static ﬁle server
var uri = url.parse(request.url).pathname;
var filename = path.join(process.cwd(), uri);

// Then read file

}).listen(8080);

HTTP static ﬁle server (cont’d)
path.exists(filename, function(exists) {
f(!exists) {
i
response.sendHeader(404, {"Content-Type": "text/plain"});
response.write("404 Not Foundn");
response.close();
return;

}
s.readFile(filename, "binary", function(err, file) {
f
if(err) {
response.sendHeader(500, {"Content-Type": "text/plain"});
response.write(err + "n");
response.close();
return;
}
response.sendHeader(200);
response.write(file, "binary");
response.close();
);
}
});

Easy comet example
var http = require('http');
var spawn = require('child_process').spawn;

response.writeHead(200, {'Content-Type': 'text/plain'});
var child_process = spawn('tail', ['-F', '/var/log/system.log']);

request.connection.on('end', function() {
child_process.kill();
});

child_process.stdout.on('data', function(data) {
console.log(data.toString());
response.write(data);
});

}).listen(8080);

Long polling example
var http = require("http");
var requests = [];

// store the response so we can respond later
requests.push(response);
}).listen(8000);

setInterval(function() {
// respond to each request
while (requests.length) {
response = requests.shift();
response.writeHead(200, { "Content-Type": "text/plain" });
response.end("Hello, World!");
}
}, 2000);

Great community support
• Reminds me of Ruby community

• GitHub project wiki has lots of resources

• Most of the related projects are on GitHub

• npm is a package manager for node

Some books under working
• Node.js Up and Running

• Mastering Node.js

• The Node Beginner Book

How to Node?
• Pick one of the book or tutorials online

• Do examples of event-driven programming model

• Start to code your project

• Got problem? Read the API, and move on

• Finally, you learn how to node

Introduction to Node.js

Related slideshows

More Related Content

Introduction to Node.js