Node.js Dojo

Node.jsGrenoble JS - 2011/10/19

Who am I?

Who am I?Jeff Mesnil

Who am I?Jeff MesnilSoftware Developer at Bestofmedia

Who am I?Jeff MesnilSoftware Developer at Bestofmediahttp://jmesnil.net/

Who am I?Jeff MesnilSoftware Developer at Bestofmediahttp://jmesnil.net/jmesnil@gmail.com

Who am I?Jeff MesnilSoftware Developer at Bestofmediahttp://jmesnil.net/jmesnil@gmail.comtwitter: @jmesnil

Previously

PreviouslyRed Hat / JBoss

PreviouslyRed Hat / JBossHornetQ messaging server

PreviouslyRed Hat / JBossHornetQ messaging serverWritten in Java

PreviouslyRed Hat / JBossHornetQ messaging serverWritten in JavaConcurrency

PreviouslyRed Hat / JBossHornetQ messaging serverWritten in JavaConcurrencyThousands of producers/consumers

PreviouslyRed Hat / JBossHornetQ messaging serverWritten in JavaConcurrencyThousands of producers/consumersHard to write correct multithreaded code

PreviouslyRed Hat / JBossHornetQ messaging serverWritten in JavaConcurrencyThousands of producers/consumersHard to write correct multithreaded codeImpossible to prove it is correct

«Ive learned that you can never believe that a program using shared-memory concurrency (which is what threading uses) is working correctly - You can only discover that its wrong, but you can never prove that its right. ... you can never let yourself become too conﬁdent about your programming abilities when it comes to shared-memory concurrency. I would not besurprised if, sometime in the future, someone comes up with a proof to show that shared-memory concurrency programming is only possible in theory, but not in practice.» -- Bruce Eckel, Thinking in Java

Multithreading is Hard Let’s Go Shopping!

• Erlang, Scala

• Erlang, Scala • Actor Model

• Erlang, Scala • Actor Model• Clojure

• Erlang, Scala • Actor Model• Clojure • Software Transaction Model (STM)

node.js ?

http://nodejs.org/

Evented I/O for V8 JavaScript

V8From Google

V8From GoogleOpen Source JavaScript engine

V8From GoogleOpen Source JavaScript engineUsed in Google Chrome

V8From GoogleOpen Source JavaScript engineUsed in Google ChromeStandalone or embedded into any C++application

V8From GoogleOpen Source JavaScript engineUsed in Google ChromeStandalone or embedded into any C++applicationFast (for a JavaScript Engine...)

JavaScript

JavaScriptNode applications are written in JavaScript(or CoffeeScript...)

JavaScriptNode applications are written in JavaScript(or CoffeeScript...)Functions are 1st-class citizen

JavaScriptNode applications are written in JavaScript(or CoffeeScript...)Functions are 1st-class citizenWell suited for event-driven applications

JavaScriptNode applications are written in JavaScript(or CoffeeScript...)Functions are 1st-class citizenWell suited for event-driven applicationsNo standard I/O library...

Event Loopwhile (true) ready_channels = select(io_channels) for channel in ready_channels performIO(channel)

Single thread (on a single core)

Single thread (on a single core)Register interested I/O events and a callback

Single thread (on a single core)Register interested I/O events and a callbackCalled back when the event occurs

Asynchronous I/O

Read a Filevar fs = require(fs);fs.readFile(/usr/share/dict/words, utf8, function (err, data) { if (err) throw err; console.log(data);});

TCP Echo Servervar net = require(net);var server = net.createServer(function (socket) { socket.setEncoding(utf-8); socket.write("Echo serverrn"); socket.on(data, function(data) { console.log(data); socket.write(data.toUpperCase()); });});server.listen(1337, "127.0.0.1");

$ telnet localhost 1337Echo serverhello, World!!HELLO, WORLD!!

node.js is good for

node.js is good for• I/O-bound Code

node.js is good for• I/O-bound Code • DB, Web Services connectivity

node.js is good for• I/O-bound Code • DB, Web Services connectivity • Data Aggregation

node.js is good for• I/O-bound Code • DB, Web Services connectivity • Data Aggregation • Non-blocking communication

node.js is good for• I/O-bound Code • DB, Web Services connectivity • Data Aggregation • Non-blocking communication• Do a bit of I/O and let the others play

node.js is not good for

node.js is not good for• CPU-bound applications

node.js is not good for• CPU-bound applications • Computation (Fibonacci...)

node.js is not good for• CPU-bound applications • Computation (Fibonacci...) • Machine-Learning algorithm

node.js is not good for• CPU-bound applications • Computation (Fibonacci...) • Machine-Learning algorithm • ...

node.js is not good for• CPU-bound applications • Computation (Fibonacci...) • Machine-Learning algorithm • ...• Everybody has to wait its turn

Workaround is to start new processes viachild_process.fork()

Workaround is to start new processes viachild_process.fork()Data communication?

Workaround is to start new processes viachild_process.fork()Data communication?Load?

Workaround is to start new processes viachild_process.fork()Data communication?Load?Web Workers API (or Isolates à la Dart)?

Google Scraper

Google Scraper• For a query

Google Scraper• For a query • Connect to Google and fetch a result page

Google Scraper• For a query • Connect to Google and fetch a result page • Use JQuery to ﬁnd all the anchors for the results

Google Scraper• For a query • Connect to Google and fetch a result page • Use JQuery to ﬁnd all the anchors for the results • Print their URLs

$ node scraper.js "node javascript"http://nodejs.org/http://www.theregister.co.uk/2011/03/01/the_rise_and_rise_of_node_dot_js/http://www.howtocreate.co.uk/tutorials/javascript/dombasicshttp://net.tutsplus.com/tutorials/javascript-ajax/learning-serverside-javascript-with-node-js/...

// Node.js modules required to run the scraper// use npm to install them:// $ `curl http://npmjs.org/install.sh | sh`var request = require(request), jsdom = require(jsdom);

// Node.js modules required to run the scraper// use npm to install them:// $ `curl http://npmjs.org/install.sh | sh` ap per wr u est P reqvar request = require(request), HTT jsdom = require(jsdom);

// Node.js modules required to run the scraper// use npm to install them:// $ `curl http://npmjs.org/install.sh | sh` per w rap u est ver req Ser TTP thevar request = require(request), H yo n Q uer u se j jsdom = require(jsdom);

// remove node and the ﬁle name from the arguments listvar args = process.argv.slice(2);if (args.length != 1) { console.log(Usage: node scraper.js <query sentence>); process.exit(1);}// the query to search on Googlevar query = escape(args[0]);// Google URL that will be request and whose content will be scrapedvar url = http://www.google.com/search?q= + query;

request({ uri: url }, function (error, response, body) { // nothing to do if we get an error from Google if (error) { console.log(Error when contacting google.com: + error); process.exit(2); } // idem if the response is not OK if (response && response.statusCode !== 200) { console.log(Did not get a correct response from Google: + response); process.exit(2); } ...});

po nserequest({ uri: url }, function (error, response, body) { a res e get w // nothing to do if we get an error from Google w hen b ack if (error) { call console.log(Error when contacting google.com: + error); process.exit(2); } // idem if the response is not OK if (response && response.statusCode !== 200) { console.log(Did not get a correct response from Google: + response); process.exit(2); } ...});

po nserequest({ uri: url }, function (error, response, body) { a res e get w // nothing to do if we get an error from Google w hen b ack if (error) { call console.log(Error when contacting google.com: + error); process.exit(2); } // idem if the response is not OK if (response && response.statusCode !== 200) { console.log(Did not get a correct response from Google: + response); process.exit(2); } b ody in the li nks the ﬁnd et’s ... l});

// use jsdom and jQuery to manipulate the DOM corresponding to the responses body jsdom.env({ html: body, scripts: [ // jQuery is loaded directly from its web site. // We could instead cache it locally for efficiency http://code.jquery.com/jquery-1.5.min.js ] }, function (err, window) { ... });

// use jsdom and jQuery to manipulate the DOM corresponding to the responses body y jsdom.env({ jQ uer up o set html: body, do mt s scripts: [ use j // jQuery is loaded directly from its web site. // We could instead cache it locally for efficiency http://code.jquery.com/jquery-1.5.min.js ] }, function (err, window) { ... });

// use jsdom and jQuery to manipulate the DOM corresponding to the responses body y jsdom.env({ jQ uer up o set html: body, do mt s scripts: [ use j // jQuery is loaded directly from its web site. // We could instead cache it locally for efficiency http://code.jquery.com/jquery-1.5.min.js ] }, function (err, window) { yc ode uer ... iliar jQ m oe s fa }); he re g

// alias jQuery object to the more familiar $var $ = window.jQuery; // print the URLS of the results listed by Google... $(a.l).each(function() { console.log($(this).attr(href)); });

Russian Dolls

Spaghetti Code?

No Silver Bullet...

Another arrow in your quiver!

«Ruby, Javascript, and Clojure are all general-purpose languages, but they each excel at certain use cases. Rubys highly dynamic nature and emphasis on beauty makes it a natural ﬁt for user-facing web apps. Node.jss evented concurrency makes it a great ﬁt for the realtimeweb. Clojure covers a new use case on the Heroku platform: components which demand correctness, performance,composability; and optionally, access to the Java ecosystem.» -- http://blog.heroku.com/archives/2011/7/5/ clojure_on_heroku

https://github.com/jmesnil/node-sampleshttps://groups.google.com/forum/?hl=fr#!forum/grenoblejs

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Node.js Dojo

by jmesnil

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