Node.jsAwesome, Lightweight, JavaScript, High Performance

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WHO AM I?

• Richard Nieuwenhuis

• 32 years old

• MediaMonks

• 7 years a Monk

• Lead of Operations / Head of development

A nice show reel (Containing a lot of NodeJS stuff)

Overview• What is Node.js

• Some small examples

• Asynchrony here, asynchrony there

• Some (popular) Node.js modules

• Socket.io

• High performance examples

• Some tips & tricks

When and by whom?• First made public in 2009

• Ryan Lienhart Dahl

• Currently at version 0.10.25*

• “Why is a progress bar so difficult?”

• “Why the heck are we polling???”

• This sheet was created 17-2-2014

What nodejs.org says• “Node.js is a platform built on Chrome's JavaScript

runtime for easily building fast, scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.”

In short how many people see it

• Server side JavaScript!

High Level Component overview

Node.jsEvent Loop

(Libuv)

V8

Where to begin?

• Download & Install Node.js• Use your favorite IDE

• Node.js API/Modules:• Built-in• Sort of API’s which expose Node functions• Allows the Node.js community to extend Node.js• Super lightweight

• Add-ons• Quite a big community• The NPM (Node Package Manager)

Some Node.js APIs/Modules

• http

• Provides basic functions for creating a server and handling requests

• https

• For setting up a secured server

• assert

• For creating unit tests for your code (NodeTDD!)

• fs

• For doing stuff with the File System

Some Node.js APIs/Modules continued

• querystring

• For parsing the query string of a request

• url

• functions for parsing and resolving URL’s

• repl: Read-Eval-Print-Loop

• Good for debugging and testing

Let’s build something simple

• Simple server

• Every “Hello World” Example starts with this.

• Read the files of a folder.

• Print the file names in the browser in sorted fashion.

• PS. Examples show Node specifics and are to illustrate points and are by no means “elegant, save” etc :-)

Create our own module: sorterservice.js

function sortFileNames(fileNames){return fileNames.sort();

}

exports.sortFileNames = sortFileNames;

- a module can be a single file

- a module can be a folder

- exports is a special object to define properties

- Can be any type: function, strings, etc

Requiring needed modules

//require the needed modules

var http = require('http');

var fs = require('fs');

var sorter = require('./sorterservice');

Create server and verify requests

http.createServer(function(req, res){ switch(req.method){ case 'POST':

console.log('This is a post request'); break;

case 'GET': switch(req.url){

case '/': readFileNames(res); break;

case '/showfiles‘:

readFileNames(res); break;

case '/favicon.ico‘: break;

} break; default:

res.setHeader('Content-Type', 'text/plain'); res.end("This method I simply do not know"); } }).listen(8888);

Let’s read the file names

function readFileNames(res){

var dirName = './files';

var html = '';

var fileNames = fs.readdirSync(dirName);

var sortedFileNames = sorter.sortFileNames(fileNames);

html += '<ol>';

for(var index in sortedFileNames){

html += '<li>' + sortedFileNames[index] + '</li>';

}

html += '</ol>';

sendFileNames(res, html);

}

One last thing & Does it work?

function sendFileNames(res, html){

res.setHeader('Content-Type', 'text/html');

res.end(html);

}

Two big things not OK hereWhich are also two important Node aspects

1) Error handling

2) A-synchronous architecture

Main problem 1

function readFileNames(res){

var dirName = './files';

var html = '';

var fileNames = [];

fileNames = fs.readdirSync(dirName);

var sortedFileNames = sorter.sortFileNames(fileNames);

html += '<ol>';

for(var index in sortedFileNames){

html += '<li>' + sortedFileNames[index] + '</li>';

}

html += '</ol>';

sendFileNames(res, html);

}

What did we see?

• The server crashed and Node stopped running

• A lot less forgiving than PHP for example

• Not OK during a super bowl commercial where millions of Dollars are spend ;-)

Tip: Look at the Node.js module forever

In this case a simple

if (fs.existsSync(dirName)){

fileNames = fs.readdirSync(dirName);

}

Would suffice….

• Defensive programming is super important in Node

• Verify everything!

• Valid user input

• Expect the unexpected (even if you expect otherwise)

• Act on any error that may occur (and log it)

• Have a process in place to restart node just to be sure (forever module)

“Problemo” numero dos

fs.readdirSync(dirName);

Node is a single threaded running process.

Synchronous development

• Blocking/Synchronous requests are bad

• It will “block” the continuation of your logic for the amount of time the blocking request is active (requesting a JSON file for example)

• On the server you basically have the same problems

• But it will affect all visitors immediately when one request is stalling

• Can ultimately lead to a crashing server

Synchronous developmenthttp.createServer(function(req, res){

switch(req.method){

case 'POST':

console.log('This is a post request');

break;

case 'GET':

//”Select *” all 200K users from the database

//Give it back to the response

}

}).listen(8888);

Continued

CPU

processData()

doQuery()Request

Pffff, I need to return 200K

rows?

Going to take me a while!

DB

Cpu to r2: Sorry, I am doing

nothing, but the DB is sooooo

slowww

Request 2

Cpu time

The Event Loop

CPU

processData()

Request

Pffff, I need to return 200K

rows?

Going to take me a while!

DB

CPU to r2: thanks man! I am

processing your request

Request 2

Take this event loop!: doQuery(cb)

E loop

callback

A-Synchronous Node development

A lot of Node functions have a-synchronous versions.

fs.readdir(dirName, function(err, data){ if (err){

console.log(); }

var sortedFileNames = sorter.sortFileNames(data);

//The other code

---------------------------

http.createServer(function(req, res){……

A-Synchronous Node development

• A-synchronize as much as possible to keep the main process as “free” as possible.

• Much more necessary when it is a high-performance environment

• It is not the holy grail! Keep the Big O in mind: for (var x = 0; x < 25.5Billion; x++)

• Sequencing & parallel

• Can become quite messy and unreadable

A highly unlikely hypothetical situation

• Read the files from Dir A

• Merge the content of all files of Dir A into one file

• Read the files from Dir B

• Append the content of step 1 to all files in Dir B

• Store these results in the Database

Would look something like this

aSynReadDir('A/', function(files) {

mergeFiles(files, function(fileContents) {

aSynReadDir('B/', function(files) {appendFiles(fileContents, files, function(appendedFiles) {

insertIntoDatabase(appendedFiles, function() {});

});});

});});

Useful Node Modules: Socket.io

• Latest browsers support Web sockets

• IE10+

• Chrome

• FireFox

• “Weirdly” on Android only starting from 4.4…

• Socket.io leverages the Web socket technology for bi-directional communication between clients & servers:

• With degradability in place for the “older” browsers!

Socket.io continued

• Very nice for real time applications with a lot of concurrent users.

• Browser based games where you mobile is the controller

• Second screen applications

• Updating the client:

• Chat

• Real time statistics

• News updates

• Etc

Small example (Server)

var server = http.createServer(function(req, res){

//code here

});

var io = socketio.listen(server);

function sendRandomMessage(){

var index = Math.floor((Math.random()*4));

io.sockets.send(words[index]);

}

Small example (Client)

var socket = io.connect();

socket.on('message', function (message) {

console.log(‘I received the message ' + message);

var m = document.createElement('p');

m.innerText = message;

document.getElementById('text').appendChild(m);

});

Event Listener

socket.on('message', function (message)……

socket.emit(‘fired’, {message: yep, you are fired});

Other Useful Node Modules  "dependencies": {

        "express": "3.4.7", // Web Framework        "express-validator": "1.0.1",         "request": "2.25.0", //        "redis": "0.10.0", //Redis: High performance in memory DB        "hiredis": "0.1.16", // To make Redis even faster with C written stuff        "redis-sentinel": "0.0.5", // Redis failover        "http-auth": "*", //for authentication        "openid": "0.5.5", //Open ID client        "statsd-client": "*", //NodeJS deamon for logging request statistics        "facebook-node-sdk": "0.2.0",        "librato-metrics": "0.0.7",        "statsd-client": "0.0.15"    }

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THANK YOU!• We are looking for new awesome

developers!

• Questions: richard@mediamonks.com