About Node.js

INTRO TO NODE.JS- L E V E L O N E -

INTRO TO NODE.JS
WHAT IS NODE.JS?
It’s fast because it’s mostly C code
Allows you to build scalable network
applications using JavaScript on the server-side.
V8 JavaScript Runtime
Node.js

INTRO TO NODE.JS
WHAT COULD YOU BUILD?
• Websocket Server
• Fast File Upload Client
• Ad Server
• Any Real-Time Data Apps
Like a chat server

INTRO TO NODE.JS
WHAT IS NODE.JS NOT?
• A Web Framework
• For Beginners It’s very low level
• Multi-threaded
You can think of it as a single threaded server

INTRO TO NODE.JS
OBJECTIVE: PRINT FILE CONTENTS
This is a “Callback”
Read file from Filesystem, set equal to “contents”
Print contents
• Blocking Code
• Non-Blocking Code
Do something else
Read file from Filesystem
whenever you’re complete, print the contents
Do Something else

console.log(contents);
INTRO TO NODE.JS
BLOCKING VS NON-BLOCKING
var contents = fs.readFileSync('/etc/hosts');
console.log('Doing something else');
• Blocking Code
• Non-Blocking Code
console.log('Doing something else');
Stop process until complete
fs.readFile('/etc/hosts', function(err, contents) {
});

fs.readFile('/etc/hosts', function(err, contents) {
});
INTRO TO NODE.JS
CALLBACK ALTERNATE SYNTAX
var callback = function(err, contents) {
}
fs.readFile('/etc/hosts', callback);
Same as

INTRO TO NODE.JS
BLOCKING VS NON-BLOCKING
blocking
0s
non-blocking
10s5s
0s 10s5s
fs.readFile('/etc/hosts', callback);
fs.readFile('/etc/inetcfg', callback);
var callback = function(err, contents) {
}

hello.js
NODE.JS HELLO DOG
$ curl http://localhost:8080
Hello, this is dog.
How we require modules
Status code in header
Response body
Close the connection
Listen for connections on this port
$ node hello.js Run the server
var http = require('http');
http.createServer(function(request, response) {
response.writeHead(200);
response.write("Hello, this is dog.");
response.end();
}).listen(8080);
console.log('Listening on port 8080...');
Listening on port 8080...

THE EVENT LOOP
}).listen(8080);
console.log('Listening on port 8080...');
Starts the Event Loop when finished
...
Known Events
request
Checking
for
Events
Run the Callback

INTRO TO NODE.JS
WHY JAVASCRIPT?
“JavaScript has certain characteristics that make it very
different than other dynamic languages, namely that it has
no concept of threads. Its model of concurrency is
completely based around events.” - Ryan Dahl

THE EVENT LOOP
Known Events
requestChecking
for
Events
connection
close
Event Queue
close
request
Events processed one at a time

INTRO TO NODE.JS
WITH LONG RUNNING PROCESS
Represent long running process
}).listen(8080);
response.write("Dog is done.");
response.end();
setTimeout(function(){
}, 5000); 5000ms = 5 seconds
response.write("Dog is running.");

INTRO TO NODE.JS
TWO CALLBACKS HERE
request
timeout
}).listen(8080);
response.end();
}, 5000);

TWO CALLBACKS TIMELINE
0s 10s5s
Request comes in, triggers request event
Request Callback executes
setTimeout registered
setTimeout registered
triggers setTimeout event
setTimeout Callback executes
setTimeout Callback
request
timeout

WITH BLOCKING TIMELINE
0s 10s5s
setTimeout executed
Request comes in, waits for server
Request comes in
setTimeout Callback executed
Wasted Time

INTRO TO NODE.JS
• Calls out to web services
TYPICAL BLOCKING THINGS
• Reads/Writes on the Database
• Calls to extensions

EVENTS
EVENTS IN THE DOM
The DOM
The DOM triggers Events
click
events
you can listen for those events
submit
hover
When ‘click’ event is triggered
attach
$("p").on("click", function(){ ... });

EVENTS
EVENTS IN NODE
EventEmitter
Many objects in Node emit events
net.Server
request
event
EventEmitter
fs.readStream
data
event

EVENTS
CUSTOM EVENT EMITTERS
var logger = new EventEmitter();
logger.emit('error', 'Spilled Milk');
ERR: Spilled Milk
logger.emit('error', 'Eggs Cracked');
var EventEmitter = require('events').EventEmitter;
error warn info
listen for error event
logger.on('error', function(message){
console.log('ERR: ' + message);
});
ERR: Eggs Cracked
events

EVENTS
EVENTS IN NODE
EventEmitter
Many objects in Node emit events
net.Server
request
event
When ‘request’ event is emitted
function(request, response){ .. }
emit
attach

EVENTS
HTTP ECHO SERVER
http.createServer(function(request, response){ ... });
But what is really going on here?
http://nodejs.org/api/

EVENTS
BREAKING IT DOWN

EVENTS
ALTERNATE SYNTAX
var server = http.createServer();
function(request, response){ ... });server.on('request',
This is how we add
Same as
function(){ ... });server.on('close',
add event listeners

STREAMS- L E V E L T H R E E -

S T R E A M S
WHAT ARE STREAMS?
Start Processing
Immediately
Streams can be readable, writeable, or both

S T R E A M S
STREAMING RESPONSE
Our clients receive "Dog is running."
"Dog is done."
(5 seconds later)
}).listen(8080);
response.end();
}, 5000);
readable stream writable stream

S T R E A M S
HOW TO READ FROM THE REQUEST?
EventEmitter
Readable Stream data
events
emit
Lets print what we receive from the request.
request.on('data', function(chunk) {
console.log(chunk.toString());
});
response.end();
}).listen(8080)
request.on('end', function() {
});
end

S T R E A M S
LETS CREATE AN ECHO SERVER
});
response.end();
}).listen(8080)
});
response.write(chunk); request.pipe(response);

S T R E A M S
LETS CREATE AN ECHO SERVER!
}).listen(8080)
request.pipe(response);
$ curl -d 'hello' http://localhost:8080
Hello on client
cat 'bleh.txt' | grep 'something'
Kinda like on the command line

S T R E A M S
READING AND WRITING A FILE
var fs = require('fs');
var file = fs.createReadStream("readme.md");
var newFile = fs.createWriteStream("readme_copy.md");
require filesystem module
file.pipe(newFile);

S T R E A M S
UPLOAD A FILE
request.pipe(newFile);
}).listen(8080);
$ curl --upload-file readme.md http://localhost:8080
uploaded!
response.end('uploaded!');
});

THE AWESOME STREAMING
client storage
server
original file
transferred file
non-blocking
0s 10s5s

BACK PRESSURE!
client storage
server
original file
transferred file
Writable stream slower
than readable stream
Using pipe solves this problem

THINK OF A MILK JUG
milkStream.pause();
milkStream.resume();
});
Once milk jug is drained

PIPE SOLVES BACKPRESSURE
readStream.resume();
});
Pause when writeStream is full
writeStream.on('drain', function(){
readStream.on('data', function(chunk) {
writeStream.write(chunk);
});
var buffer_good =
if (!buffer_good) readStream.pause(); returns false
if kernel buffer full
Resume when ready to write again
readStream.pipe(writeStream);
All encapsulated in

S T R E A M S
FILE UPLOADING PROGRESS

S T R E A M S
FILE UPLOADING PROGRESS
$ curl --upload-file file.jpg http://localhost:8080
progress: 3%
progress: 6%
progress: 9%
progress: 12%
progress: 13%
...
progress: 99%
progress: 100%
Outputs:
• HTTP Server
• File System
We’re going to need:

S T R E A M S
DOCUMENTATION http://nodejs.org/api/
Stability Scores

S T R E A M S
REMEMBER THIS CODE?
}).listen(8080);
response.end('uploaded!');
});

S T R E A M S
REMEMBER THIS CODE?
}).listen(8080);
...
uploadedBytes += chunk.length;
var progress = (uploadedBytes / fileBytes) * 100;
response.write("progress: " + parseInt(progress, 10) + "%n");
});
var uploadedBytes = 0;
var fileBytes = request.headers['content-length'];

S T R E A M S
SHOWING PROGRESS

MODULES
REQUIRING MODULES
http.js
How does it find these files?
var fs = require('fs'); fs.js
How does ‘require’ return the libraries?

MODULES
LETS CREATE OUR OWN MODULE
custom_hello.js custom_goodbye.js
app.js
exports = hello;
var hello = require('./custom_hello');
hello();
exports defines what require returns
var hello = function() {
console.log("hello!");
}
exports.goodbye = function() {
console.log("bye!");
}
var gb = require('./custom_goodbye');
gb.goodbye();
require('./custom_goodbye').goodbye(); If we only need to call once

MODULES
EXPORT MULTIPLE FUNCTIONS
my_module.js
app.js
var foo = function() { ... }
var bar = function() { ... }
exports.foo = foo
exports.bar = bar
var myMod = require('./my_module');
myMod.foo();
myMod.bar();
my_module.js
foo
bar
var baz = function() { ... }
baz
“private”

MODULES
MAKING HTTP REQUESTS
app.js
logs response body
begins request
var options = {
host: 'localhost', port: 8080, path: '/', method: 'POST'
}
var request = http.request(options, function(response){
response.on('data', function(data){
console.log(data);
});
});
request.end();
request.write(message);
finishes request
var message = "Here's looking at you, kid.";

MODULES
ENCAPSULATING THE FUNCTION
app.jsvar http = require('http');
var makeRequest = function(message) {
var options = {
host: 'localhost', port: 8080, path: '/', method: 'POST'
}
var request = http.request(options, function(response){
response.on('data', function(data){
console.log(data);
});
});
request.end();
}
makeRequest("Here's looking at you, kid.");
request.write(message);
Text

MODULES
CREATING & USING A MODULE
make_request.jsvar http = require('http');
var makeRequest = function(message) {
}
exports = makeRequest;
...
app.jsvar makeRequest = require('./make_request');
makeRequest("Here's looking at you, kid");
makeRequest("Hello, this is dog");
Where does require look for modules?

MODULES
REQUIRE SEARCH
var make_request = require('make_request')
/Home/eric/my_app/app.js
• /Home/eric/my_app/node_modules/
var make_request = require('./make_request')
var make_request = require('../make_request')
var make_request = require('/Users/eric/nodes/make_request')
• /Home/eric/node_modules/make_request.js
• /Home/node_modules/make_request.js
• /node_modules/make_request.js
look in same directory
look in parent directory
Search in node_modules directories

MODULES
NPM: THE USERLAND SEA
Package manager for node
• Comes with node
• Module Repository
• Dependency Management
• Easily publish modules
• “Local Only”
“Core” is small. “Userland” is large.

MODULES
INSTALLING A NPM MODULE
$ npm install request https://github.com/mikeal/request
In /Home/my_app
Home my_app requestnode_modules
Installs into local node_modules directory
var request = require('request');
In /Home/my_app/app.js
Loads from local node_modules directory

MODULES
LOCAL VS GLOBAL
Global npm modules can’t be required
$ npm install coffee-script -g
Install modules with executables globally
$ coffee app.coffee
var coffee = require('coffee-script');
$ npm install coffee-script
var coffee = require('coffee-script');
global
Install them locally

MODULES
FINDING MODULES
npm registry
$ npm search request
npm command line
github search
toolbox.no.de

MODULES
DEFINING YOUR DEPENDENCIES
my_app/package.json
version number
$ npm install
my_app connectnode_modules
Installs into the node_modules directory
{
"name": "My App",
"version": "1",
"dependencies": {
"connect": "1.8.7"
}
}

MODULES
DEPENDENCIES
my_app connectnode_modules
Installs sub-dependencies
connect node_modules qs
connect node_modules mime
connect node_modules formidable
No conflicting modules!
"dependencies": {
"connect": "1.8.7"
}
my_app/package.json

MODULES
SEMANTIC VERSIONING
"connect": "1.8.7" 1 8 7
Major Minor Patch
. .
http://semver.org/
"connect": "~1.8.7" >=1.8.7 <1.9.0 Considered safe
"connect": "~1.8" >=1.8 <2.0.0 API could change
"connect": "~1" >=1.0.0 <2.0.0 Dangerous
Ranges

EXP RESS
EXPRESS
“Sinatra inspired web development framework for Node.js --
insanely fast, flexible, and simple”
• Easy route URLs to callbacks
• Middleware (from Connect)
• Environment based configuration
• Redirection helpers
• File Uploads

EXP RESS
INTRODUCING EXPRESS
$ npm install express
var express = require('express');
var app = express.createServer();
app.get('/', function(request, response) {
response.sendfile(__dirname + "/index.html");
});
app.listen(8080);
$ curl http://localhost:8080/
> 200 OK
root route
current directory

EXP RESS
EXPRESS ROUTES
app.js
route definition
get the last 10 tweets for screen_name
pipe the request to response
var request = require('request');
var url = require('url');
app.get('/tweets/:username', function(req, response) {
var username = req.params.username;
options = {
protocol: "http:",
host: 'api.twitter.com',
pathname: '/1/statuses/user_timeline.json',
query: { screen_name: username, count: 10}
}
var twitterUrl = url.format(options);
request(twitterUrl).pipe(response);
});

EXP RESS
EXPRESS TEMPLATES
app.js
tweets.ejs
app.get('/tweets/:username', function(req, response) {
...
request(url, function(err, res, body) {
var tweets = JSON.parse(body);
response.render('tweets.ejs', {tweets: tweets, name: username});
});
});
<h1>Tweets for @<%= name %></h1>
<ul>
<% tweets.forEach(function(tweet){ %>
<li><%= tweet.text %></li>
<% }); %>
</ul>

EXP RESS
TEMPLATE LAYOUTS
<!DOCTYPE html>
<html>
<head>
<title>Tweets</title>
</head>
<body>
<%- body %>
</body>
</html>
<h1>Tweets for @<%= name %></h1>
<ul>
<% tweets.forEach(function(tweet){ %>
<li><%= tweet.text %></li>
<% }); %>
</ul>
tweets.ejs
layout.ejs

SOCKET.IO
WEBSOCKETS
browser traditional server
Traditional request/response cycle

Using duplexed websocket connection
SOCKET.IO
WEBSOCKETS
browser socket.io

SOCKET.IO
SOCKET.IO FOR WEBSOCKETS
var socket = require('socket.io');
var app = express.createServer();
var io = socket.listen(app);
Abstracts websockets with fallbacks
io.sockets.on('connection', function(client) {
});
console.log('Client connected...');
<script src="/socket.io/socket.io.js"></script>
var server = io.connect('http://localhost:8080');
<script>
</script>
$ npm install socket.io
app.js
index.html

SOCKET.IO
SENDING MESSAGES TO CLIENT
});
console.log('Client connected...');
<script src="/socket.io/socket.io.js"></script>
<script>
</script>
app.js
index.html
client.emit('messages', { hello: 'world' });
server.on('messages', function (data) {
});
alert(data.hello);
emit the ‘messages’ event on the client
listen for ‘messages’ events

SOCKET.IO
SENDING MESSAGES TO SERVER
});
<script>
</script>
app.js
index.html
client.on('messages', function (data) {
});
console.log(data);
$('#chat_form').submit(function(e){
var message = $('#chat_input').val();
socket.emit('messages', message);
});
listen for ‘messages’ events
emit the ‘messages’ event on the server

SOCKET.IO
BROADCASTING MESSAGES
clients
server
app.js
socket.broadcast.emit("message", 'Hello');

SOCKET.IO
});
<script>
</script>
app.js
index.html
client.on('messages', function (data) {
});
...
broadcast message to all other clients connected
client.broadcast.emit("messages", data);
server.on('messages', function(data) { insertMessage(data) });
insert message into the chat

SOCKET.IO

SOCKET.IO
SAVING DATA ON THE SOCKET
});
<script>
</script>
app.js
index.html
client.on('join', function(name) {
client.set('nickname', name);
});
set the nickname associated
with this client
server.on('connect', function(data) {
$('#status').html('Connected to chattr');
nickname = prompt("What is your nickname?");
server.emit('join', nickname);
});
notify the server of the
users nickname

SOCKET.IO
SAVING DATA ON THE CLIENT
});
app.js
});
set the nickname associated
with this client
client.on('messages', function(data){
});
client.broadcast.emit("chat", name + ": " + message);
client.get('nickname', function(err, name) {
});
get the nickname of this client before broadcasting message
broadcast with the name and message

SOCKET.IO
SAVING DATA ON THE CLIENT

PERSISTING DATA- L E V E L S E V E N -

P E R S I S T I N G D A T A
RECENT MESSAGES

});
});
});
RECENT MESSAGES
client.broadcast.emit("chat", name + " joined the chat");
});
client.on("messages", function(message){
client.get("nickname", function(error, name) {
client.broadcast.emit("messages", name + ": " + message);
app.js

});
});
});
STORING MESSAGES
client.on("messages", function(message){
client.get("nickname", function(error, name) {
app.js
storeMessage(name, message);
var messages = []; store messages in array
var storeMessage = function(name, data){
messages.push({name: name, data: data});
if (messages.length > 10) {
messages.shift();
}
}
add message to end of array
if more than 10 messages long,
remove the last one
when client sends a message
call storeMessage

EMITTING MESSAGES
});
app.js
});
messages.forEach(function(message) {
client.emit("messages", message.name + ": " + message.data);
}); iterate through messages array
and emit a message on the connecting
client for each one
...

PERSISTING STORES
• MongoDB
• CouchDB
• PostgreSQL
• Memcached
• Riak
All non-blocking!
Redis is a key-value store

REDIS DATA STRUCTURES
Strings SET, GET, APPEND, DECR, INCR...
Hashes HSET, HGET, HDEL, HGETALL...
Lists LPUSH, LREM, LTRIM, RPOP, LINSERT...
Sets SADD, SREM, SMOVE, SMEMBERS...
Sorted Sets ZADD, ZREM, ZSCORE, ZRANK...
data structure commands

REDIS COMMAND DOCUMENTATION

NODE REDIS

client.get("message1", function(err, reply){
console.log(reply);
});
REDIS
key value
"hello, yes this is dog"
var redis = require('redis');
var client = redis.createClient();
client.set("message1", "hello, yes this is dog");
client.set("message2", "hello, no this is spider");
commands are non-blocking
$ npm install redis

REDIS LISTS: PUSHING
Add a string to the “messages” list
client.lpush("messages", message, function(err, reply){
console.log(reply);
}); "1”
var message = "Hello, no this is spider";
console.log(reply);
}); "2”
replies with list length
Add another string to “messages”
var message = "Hello, this is dog";

REDIS LISTS: RETRIEVING
Using LPUSH & LTRIM
trim keeps first two strings
and removes the rest
Retrieving from list
client.lrange("messages", 0, -1, function(err, messages){
console.log(messages);
})
["Hello, no this is spider", "Oh sorry, wrong number"]
replies with all strings in list
var message = "Oh sorry, wrong number";
client.ltrim("messages", 0, 1);
});

CONVERTING MESSAGES TO REDIS
messages.push({name: name, data: data});
if (messages.length > 10) {
messages.shift();
}
}
Let’s use the List data-structure
app.js

CONVERTING STOREMESSAGE
}
var redisClient = redis.createClient();
var message = JSON.stringify({name: name, data: data});
redisClient.lpush("messages", message, function(err, response) {
redisClient.ltrim("messages", 0, 10);
});
keeps newest 10 items
app.js
need to turn object into string to store in redis

OUTPUT FROM LIST
});
});
app.js

OUTPUT FROM LIST
});
});
redisClient.lrange("messages", 0, -1, function(err, messages){
messages = messages.reverse();
message = JSON.parse(message);
});
app.js
reverse so they are emitted
in correct order
parse into JSON object

IN ACTION

CURRENT CHATTER LIST
Sets are lists of unique data
client.sadd("names", "Dog");
client.sadd("names", "Spider");
client.sadd("names", "Gregg");
client.srem("names", "Spider");
client.smembers("names", function(err, names){
console.log(names);
});
["Dog", "Gregg"]
reply with all members of set
add & remove members of the names set

ADDING CHATTERS
client.on('join', function(name){
client.broadcast.emit("add chatter", name);
redisClient.sadd("chatters", name);
});
app.js
notify other clients a chatter has joined
add name to chatters set
index.htmlserver.on('add chatter', insertChatter);
var insertChatter = function(name) {
var chatter = $('<li>'+name+'</li>').data('name', name);
$('#chatters').append(chatter);
}

ADDING CHATTERS (CONT)
client.on('join', function(name){
client.broadcast.emit("add chatter", name);
redisClient.sadd("chatters", name);
});
app.js
notify other clients a chatter has joined
add name to chatters set
emit all the currently logged in chatters
to the newly connected client
redisClient.smembers('names', function(err, names) {
names.forEach(function(name){
client.emit('add chatter', name);
});
});

REMOVING CHATTERS
client.on('disconnect', function(name){ app.js
index.html
client.get('nickname', function(err, name){
client.broadcast.emit("remove chatter", name);
redisClient.srem("chatters", name);
});
});
remove chatter when they disconnect from server
server.on('remove chatter', removeChatter);
var removeChatter = function(name) {
$('#chatters li[data-name=' + name + ']').remove();
}

WELCOME TO CHATTR

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