NODEJS(1)Some Introduction and helloworld
NODEJS(1)Some Introduction and helloworld

Some frameworks related node.js: Express, Geddy.

JavaScript and Node.js
JavaScript is not only the frontend things, and backend things are not only related to ruby, PHP, Java.

Server-side JavaScript
Node.js really is just another context: it allows you to run JavaScript code in the backend, outside a browser. Thus, Node.js is based on google V8 VM, and is really two things: a runtime environment and a library.

Install Node.js
Download the windows installer with this URL http://nodejs.org/dist/v0.6.12/node-v0.6.12.msi.
And the source code is here: http://nodejs.org/dist/v0.6.12/node-v0.6.12.tar.gz
Or we can get the source code from git
>git clone https://github.com/joyent/node.git nodejs
>cd nodejs
>git checkout v0.6.12
>vcbuild.bat   // build on windows
>vcbuild.bat test

It is not wise to run these kind of commands on windows system. I just go with msi installation file. The install location is as follow:
C:\Program Files (x86)\nodejs, double click the exe file node.exe and type command to verify the installation
>process.versions
{ node: '0.6.12',
  v8: '3.6.6.24',
  ares: '1.7.5-DEV',
  uv: '0.6',
  openssl: '0.9.8r' }
>

Hello World Sample
find a file named helloworld.js and type in
console.log("Hello Karl");

run the application with command line
>node.exe helloworld.js

The Application Upload File
We want to serve web pages, therefore we need an HTTP server.
We need some kind of router in order to map requests to request handlers.
Request handlers.
Request data handling.
Upload handling.

Things are different with PHP/JAVA, we not only implement our application, we also implement the whole HTTP server.

A basic HTTP server
server.js holds all the server codes.
var http = require("http");

http.createServer(function(request, response) {
  response.writeHead(200, {"Content-Type": "text/plain"});
  response.write("Hello World");
  response.end();
}).listen(8888);

Run these file and visit http://localhost:8888, that is really amazing.

Analyzing our HTTP server
var http = require("http"); brings the http module in node.js with name http.

var server = http.createServer(function(request, response) {
  response.writeHead(200, {"Content-Type": "text/plain"});
  response.write("Hello World");
  response.end();
});
server.listen(8888);

The method createServer will create a server.

Passing functions around
function say(word){
console.log(word);
}

function execute(someFunction, value){
someFunction(value);
}

execute(say, "Good");

We can, as we just did, pass a function as a parameter to another function by its name.

How function passing makes our HTTP server work
var http = require("http");

function onRequest(request, response) {
  response.writeHead(200, {"Content-Type": "text/plain"});
  response.write("Hello World");
  response.end();
}

var server = http.createServer(onRequest);
server.listen(8888);

We will refactor the codes like this.

Event-driven callbacks
function onRequest(request, response) {
  console.log("Request received.");
  response.writeHead(200, {"Content-Type": "text/plain"});
  response.write("Hello World");
  response.end();
}

var server = http.createServer(onRequest);
server.listen(8888);

Event-driven asynchronous server-side JavaScript with callbacks