How to Write Big Apps (Richard Rodger NodeDublin 2012)

HOW TO
WRITE
BIG APPS.
Richard Rodger
@rjrodger
Friday 26 October 2012

Node.js apps
are getting
bigger.

So, how do
you scale?
‣be stateless,
‣lots of little processes,
‣funky V8 options,
‣...

How do you
scale this?


Let's write a
class for
Cars.

Classical
function Car( params ) {
this.color = params.color || "red"
this.marque = params.marque || "Ferrari"
this.model = params.model || "Testarossa"
this.cylinders = params.cylinders || 12
this.timeto60 = params.timeto60 || 5.2 // seconds
}

Car.prototype.drive = function() {
console.log( "vrooom!" )
}

var car = new Car({color:"yellow"})
car.drive()


Classical
this.color = params.color || "red"
this.marque = params.marque || "Ferrari"
this.model = params.model || "Testarossa"
this.cylinders = params.cylinders || 12
this.timeto60 = params.timeto60 || 5.2 // seconds
}

Car.prototype.drive = function() {
console.log( "vrooom!" )
}
VO
TE
var car = new Car({color:"yellow"})
NO
car.drive()
W


var Car = {
Prototypical
color: "red",
marque: "Ferrari",
model: "Testarossa",
cylinders: 12,
timeto60: 5.2,

drive: function() {
console.log( "vrooom!", this )
}
}

var car = Object.create(Car)
car.color = "yellow"
car.drive()


var Car = {
Prototypical
color: "red",
marque: "Ferrari",
model: "Testarossa",
cylinders: 12,
timeto60: 5.2,

drive: function() {
console.log( "vrooom!", this )
}
}
VO
TE
var car = Object.create(Car)
NO
car.color = "yellow"
car.drive()
W


Functional
var self = {}

var color = params.color || "red"
var marque = params.marque || "Ferrari"
var model = params.model || "Testarossa"
var cylinders = params.cylinders || 12
var timeto60 = params.timeto60 || 5.2

self.drive = function() {
console.log( "vrooom!", self )
}
return self
}
var car = Car({color:"yellow"})
car.drive()


Functional
var self = {}

var color = params.color || "red"
var marque = params.marque || "Ferrari"
var model = params.model || "Testarossa"
var cylinders = params.cylinders || 12
var timeto60 = params.timeto60 || 5.2

self.drive = function() {
console.log( "vrooom!", self )
VO
TE
}
return self
NO
}
var car = Car({color:"yellow"})
W
car.drive()


Which one
should we
use for
Cars?

Let's play a
GAME.

Stand up.


Stand up.
Everybody.

Is this a car?


YES NO
Stay standing. Sit down.
And stay down!


Is this a car?
It's a painting.


Which one?
‣Classical
‣Prototypical
‣Functional


Which one?
‣Classical
‣Prototypical
‣Functional
NONE!

What's wrong
with properties?
‣Color - Lego?
‣Marque - Batman brand?
‣Model - Flintstones?
‣Cylinders - Star Wars hover car?
‣timeto60 - Model T max is 45mph

Classes
are
ideal
Platonic
forms.


Think of the ideal
triangle.
‣Sides - 3!
‣Points - 3!
‣Total of Angles - 180°!


Think of the ideal
triangle.
‣Sides - 3!
‣Points - 3!
‣Total of Angles - 180°!
Now picture it in
your mind.

Plato was
wrong.
Ideal forms do
not exist.

George
Berkeley

berkeley.edu
same guy

also Irish!

Inventor of...


There is no
mental image
of a ideal
triangle.

Classes suck.
Objects are ok.

Classes suck.
Objects are ok.
i nh
eritan ce


Classes suck.
refac
torin
Objects are ok.
i nh
eritanc eg


Classes suck.
refac
torin
archi
tectu

Objects are ok.
itanc eg re
er
i nh


on
Classes suck.

lati
archi

u
aps
refac tectu

enc
torin
Objects are ok.
itanc eg re
er
i nh


on
Classes suck.
sch

lati
e
archi
ma

u
s

aps
refac tectu

enc
torin
Objects are ok.
itanc eg re
er
i nh


on
Classes suck.
sch

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ma

u
s

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aps
refac tectu

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torin
Objects are ok.
itanc eg

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on
Classes suck.
sch

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u
s

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it t
refac tectu

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est
torin
Objects are ok.
eg

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itanc

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on
Classes suck.
sch

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e
archi
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s

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Objects are ok.
eg encies

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itanc pen d

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re
er de
i nh


Something is
wrong with
modeling a
car.

But you can
still drive all
those cars.

It's not what
you are.
It's what you
do.

What does your
app want to do?
‣Register a new user,
‣Place an order,
‣Call an external service,
‣Save and load data,
‣...

This is JavaScript
JSON function JSON

OUTPUT,
A command asynchronously,
INPUT for your app, of course
(mostly in- that
memory objects) "does stuff"


How do you find the
right "thing to do"?


How do you find the
right "thing to do"?
PATTERN
MATCHING!

{
thing: "product",
cmd: "save",

... other fields
doSave()
}

{
thing: "product",
cmd: "load",

... other fields
doLoad()
}


Define your
"business logic" in
terms of these
commands.

What do you get as
the pay off?


Really easy testing.
Verify the returned
JSON and you're
done.

A distributed system,
if you need it.
That gives you scale
too.

Completely
decoupled
commands that never
need to know about
each other.

Plugins for free - just
bundle up a few
related commands.
Organize your code!

middleware-style
layering - e.g. add a
caching layer by
matching data
storage commands.

Stay in control -
tracing, logging,
throttling,
permissions, special
cases - all easy.

Documentation - just
list all the commands
and the JSON they
expect.

Code!
Open sourced at
http://senecajs.org
npm install seneca


Define and call a command.
var seneca = require('seneca')()

// define a command
seneca.add({role:'math', cmd:'sum'},
function(args,callback) {
var sum = args.left + args.right
callback(null,{answer:sum})
})

// call the command
seneca.act({role:'math', cmd:'sum', left:1, right:2},
function(err,result) {
if( err ) return console.error( err )
console.log(result)
})

// prints: { answer: 3 }


Pinning an API for convenience
// define a command
seneca.add({role:'math', cmd:'sum'},
function(args,callback) {
})

// pin the API
var math = seneca.pin({role:'math',cmd:'*'})

// call the command
math.sum({left:1,right:2},
console.log(result)
})

// prints: { answer: 3 }


Plugins: commands + HTTP API.
seneca.use( function(seneca,options,callback) {
seneca.add( {role:'math', cmd:'sum'}, function(args,callback) {
})

seneca.add( {role:'math', cmd:'product'}, function(args,callback) {
var product = args.left * args.right
callback(null,{answer:product})
})

callback( null, seneca.http({ // just a connect middleware
pin: {role:'math', cmd:'*'},
map: { sum: {}, product: {} }, // GET is the default HTTP method
args: { left: parseFloat, right: parseFloat }
}))
})

var app = connect()
.use(connect.query())
.use(seneca.service())
.listen(3000)
// http://localhost:3000/api/sum?left=1&right=2


Build a distributed system
// client:
// use transport plugin to calculate product remotely
seneca.use('transport',{
pins:[ {role:'math', cmd:'product'} ]
})

// this will go out over network
seneca.act({role:'math', cmd:'product', left:3, right:4},
console.log(result)
})

// server (as per previous slide):
seneca.use('transport')
...
app.use( connect.json() )
...


Data storage (also plugin-based)
var product = seneca.make('product')
product.name = 'apple'
product.price = 100

// ActiveRecord-style
product.save$(function( err, product ) {
console.log( 'saved: '+product )

// product.id was generated for you
product.load$({id:product.id},function( err, product ) {
console.log( 'loaded: '+product )
})
})

// output:
// saved: //product:{id=286624;name=apple;price=100}
// loaded: //product:{id=286624;name=apple;price=100}

// mix-and-match in-memory, MongoDB, MySQL, PostreSQL, etc.


Also, seneca...
‣is about 18 months old
‣has detailed tracing
‣has nice error messages
‣has a REPL! @dshaw happy?
‣is used in production

Why did we built it?
builds
Minimum Viable
Products that
become big apps.

senecajs.org
@nodeseneca

Thanks!


How to Write Big Apps (Richard Rodger NodeDublin 2012)

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