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Node.js: The What, The How and The When

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Information about Node.js: The What, The How and The When
Technology

Published on March 5, 2014

Author: fitc_slideshare

Source: slideshare.net

Description

Presented live at FITC Amsterdam 2014 on Feb 24-25, 2014
More details can be found at www.FITC.ca

Node.js: The What, The How and The When
with Richard Nieuwenhuis
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Node.js Awesome, Lightweight, JavaScript, High Performance qr.net/fitc2014

WHO AM I? • Richard Nieuwenhuis • 32 years old • MediaMonks • 7 years a Monk • Lead of Operations / Head of development

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.js V8 Event Loop (Libuv)

Where to begin? • Download & Install Node.js • • Use your favorite IDE Node.js API/Modules: • • Sort of API‟s which expose Node functions • Allows the Node.js community to extend Node.js • • Built-in 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"); }

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 here Which 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 development http.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 Pffff, I need to return 200K rows? Request Cpu to r2: Sorry, I am doing nothing, but the DB is sooooo slowww Request 2 Going to take me a while! doQuery() CPU processData() Cpu time DB

The Event Loop Take this event loop!: doQuery(cb) Pffff, I need to return 200K rows? Going to take me a while! Request CPU to r2: thanks man! I am processing your request Request 2 CPU processData() E loop callback DB

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 s tatistics "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

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