1. Node.js - What is Node.js? -
Sep. 2014
Youn-Hee Han

2. What is Node.js?
A JavaScript runtime environment running Google Chrome’s V8 engine
a.k.a. a server-side solution for JS
Runs over the command line
Designed for high concurrency
Without threads or new processes
Making it really fast
Never blocks, not even for I/O
Created by Ryan Dahl starting in 2009
Node.js is a platform (is not a framework)
Express is a framework for Node.js 참고

3. What is Node.js?
Goal is to provide an easy way to build scalable network programs.
It makes communication between client and server happen in same language (JavaScript)
Node is a platform for writing JavaScript applications outside web browsers.
There is no DOM built into Node, nor any other browser capability.
Node is actually programmed in C.
Because of the nature of C, Node can perform amazingly well when dealing with networking and OS system calls

4. Asynchronous and evented
In the browser
Asynchronous Ajax request using XMLHttpRequest
I/O doesn’t block execution
Callback function
The code was not written like this
I/O blocks execution until finished
$.post('/resource.json', function (data) {
console.log(data);
});
// script execution continues
var data = $.post('/resource.json');
console.log(data);

5. Concurrency: Event Loop
Instead of threads, Node uses an event loop with a stack
Alleviates overhead of context switching
Event loop as a language construct instead of as a library
It process each request as events
E.g., HTTP server doesn’t wait for the IO operation to complete while it can handle other request at the same time.
To avoid blocking, it makes use of the event driven nature of JavaScript by attaching callbacks to I/O requests

6. Concurrency: Event Loop
An example of non-blocking I/O in the browser

7. Concurrency: Event Loop
Thread vs. Event Loop
Threads
Event Loop
Lock application / request with listener-workers threads
only one thread, which repeatedly fetches an event
Using incoming-request model
Using queue and then processes it
multithreaded server might block the request which might involve multiple events
manually saves state and then goes on to process the next event
Using context switching
no contention and no context switches

8. Number of request per second
Node.js/HTTP vs. Apache
Node.js/HTTP
It's fast
It can handle tons of concurrent requests
It's written in JavaScript (which means you can use the same code server side and client side)
Platform
Number of request per second
PHP ( via Apache)
3187,27
Static ( via Apache )
2966,51
Node.js
5569,30

9. NGNIX vs. Apache
NGNIX
An HTTP server useing an event loop with asynchronous I/O

10. DIRTy applications DIRTy application
Data-intensive real-time application
Node.js is suitable for DIRTy application
Node.js includes a core set of modules for many types of network and file I/O.
Building blocks for I/O-based applications
HTTP, HTTPS, filesystem (POSIX), UDP, and NET (TCP).
The core is intentionally small, low-level, and uncomplicated.
Third-party modules build upon these blocks to offer greater abstractions for common problems.

11. Example 1. Simple Async App.
Node.js install
REFL 101
Node.js app using filesystem (fs) module
var fs = require('fs');
fs.readFile('./resource.json', function (er, data) {
console.log(data); })

12. Example 2. Hello World HTTP Server
An HTTP server simply responding to any request with “Hello World”
Same server to make the request event explicit
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello World\n');
}).listen(3000);
console.log('Server running at
var http = require('http');
var server = http.createServer();
server.on('request', function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello World\n'); })
server.listen(3000);
console.log('Server running at

13. Example 3. Streaming data
Stream is data distributed over time
By bringing data in chunk by chunk, the developer handles the data as it comes in instead of waiting for it all to arrive before acting.
var stream = fs.createReadStream('./resource.json')
stream.on('data', function (chunk) {
console.log(chunk) })
stream.on('end', function () {
console.log('finished')

14. Example 4. HTTP Streaming
An HTTP server streaming an image to a client
Node.js provides these DIRTy-by-default approach across multiple platforms
var http = require('http');
var fs = require('fs');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'image/png'});
fs.createReadStream('./image.png').pipe(res);
}).listen(3000);
console.log('Server running at