NodeJS:
JavaScript On The Other Side

@imcoddy
2011-07-10

Evolution of JavaScript

• JavaScript was at first designed to run everywhere
  • LiveScript for the browser clients
  • LiveWire for the backend logic
• Became a must during the Browser War
• And now, the Server Side JavaScript (SSJS) arises...

What is NodeJS?

Node.JS is not a JS framework, but a JS interpreter

• Event-driven server-side JavaScript
• Built on Google V8 engine
• Single thread, one call stack

Hello World, in Node's Way.

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

6 LoC to create a http server.

Why NodeJS?

• It unifies the language between browsers and servers
  • Possibility for code reuse
  • No need to encode/decode JSON object
• It is suited for real-time web applications
  • Persistent connection from browser to server
  • No need to maintain separate threads
• It makes better performance
  • Non I/O blocking
  • Make better use of CPU
• It is soooooooo COOL!

I/O Latency

L1: 3 cycles

L2: 14 cycles

RAM: 250 cycles

Disk: 41,000,000 cycles

Network: 240,000,000 cycles

Blocking vs Non-blocking

var result = db.query("select..");
print('I can not print until the result is returned.')
print('And the I/O is damn SLOW.');
do_something_with_result(result);

db.query("select..", function (result) {
   print('Handle the result now.');
   do_something_with_result(result);
});
print('No more waiting.');
print('Do the following right away');
do_something_else();

Struture of NodeJS

Why JavaScript Suits NodeJS?

• Callback
• Closure
• Evented

NodeJS brings the power of JavaScript to the server side.

Node express demo

The Node Ecosystem

Over 4700 watchers on Github

More than 1600 modules posted

60+ contributors

3 books in progress

1 command to install: npm install module-you-want

0.5 unstable version just released

Gets better everyday

NodeJS Limitations

Hard core CPU calculating

Large content transfer

1G memory limit due to V8 engine

Something Bothering Me

• IDE support
  • Vim is powerful, but no for everyone
  • Cloud9IDE might be a nice choice
• Unit testing framework
• Debugging & Event Handling
  • No long trace yet, hard to locate where sth went wrong
  • UncaughtException? The whole process would go down...
• Too many callbacks

NodeJS makes thinking differently

var data = {}
db.getPosts(10, function(err,posts){
 data.posts = posts;
});
db.getComments(10, function(err, comments){
 data.comments = comments;
});      
db.getTags(function(err, tags){
 data.tags = tags;
})
 
// view.render(data)
// How do you know when everything is ready?

NodeJS makes thinking differently (cont.)

function Combo(callback){
 this.callback = callback;
 this.items = 0;
}      
Combo.prototype = {
 add: function(){
   this.items++;
 },
 finishOne: function(){
   this.items--;
   this.check();
 },
 check: function(){
   if(this.items === 0){
     this.callback.apply(this);
   }
 }
};

NodeJS makes thinking differently (cont.)

var data = {};
var combo = new Combo(function(){
 view.render(data);
});
combo.add();
db.getPosts(10, function(err,posts){
 data.posts = posts;
 combo.finishOne();});
combo.add();
db.getComments(10, function(err, comments){
 data.comments = comments;
 combo.finishOne();});
combo.add()
db.getTags(function(err, tags){
 data.tags = tags;
 combo.finishOne();})  

The Long And Deep Callback Chain

self.handleQuery = function(client, message) {
 var query = message.query;
   Blip.query(query).all(function(results) {
     client.send(
       {buffer:
         results.map(
           function(msg) {
             return {message: {
                 sender: msg.sender,
                 content: msg.content,
                 }
              }
           }
        )
     });
 });
};

Well, You Can Make It Shorter With CoffeeScript

@handleQuery = (client, message) ->
 Blip.query(message.query).all (results) ->
   client.send buffer:
     results.map (msg) ->
       message:
         sender: msg.sender
         content: msg.content

Async Makes Testing Difficult

collection = 'test'
query = {}
app.count collection,query,(count)->
  doc = 
    name:1
  app.save collection,doc,()-> 
    console.log 'save in '+collection
    app.count collection,query,(result)->
       assert.eql count+1,result
collection = 'product'
// save action was supposed to execute in the 'test' collection
// but it will actually be saved in 'product' collection!

The Future Node

Windows porting with MS offical support

New networking layer

Long traceback

...

Resources

http://nodejs.org/

http://github.com/ry/node/wiki

http://howtonode.org/

http://dailyjs.com/

http://cnodejs.org/