Developing maintainable Cordova applications

Developing maintainable
Cordova applications

Ivano Malavolta
DISIM | University of L’Aquila

Roadmap
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Introduction

Backbone

I implemented all best practices and advices in this
presentation in a generic app template available here:

Require JS

Handlebars
Conclusions

https://github.com/iivanoo/cordovaboilerplate

Introduction
We are building apps, not web sites

If your code is not structured:

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it is extremely easy that your web app becomes a
big mess of HTML + CSS + JavaScript

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maintaining each part of your app asks for a
deep analysis of ALL its aspects (logic, presentation, etc.)

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you may waste a whole day due to a missing <

What we want to avoid

Imagine yourself trying to change

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how a movie should be rendered in your app
the REST API providing info about movies

Some technical advices from a real project...

How I structure my applications

MVC framework for
giving structure

File and module loader
for code modularization

Templating engine for
separation of concerns

Disclaimer
this is MY way to structure apps, you can follow yours

How I structure my applications

Backbone
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Why Backbone

Events
Models

Collections
Views
Routers
Summary

Why Backbone
Backbone gives you STRUCTURE

Why Backbone
represent
data

From the Backbone website...

manipulate
the DOM

lists
of models

Why Backbone
Additionally, Backbone provides also features for:
sync
for managing how to persist models (default is via REST)
events
for managing how data and control are exchanged within your app
router
for managing the interaction flow among views

Events
Any object communicates with other objects via events

It gives the object the ability to bind and trigger custom named events

It is extremely useful for exchanging data and control among objects

Events

Basically, each object can:

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listen to events
trigger events

Events
Two types of events:

built-in

custom
you define your own types of event

Events API
object will react to the “alert” event
(the “off” function detaches the event)

the “alert” event is fired

event parameters

Events API
Events methods:
on

listenTo
object.on(event, callback, [context])

off

object.listenTo(other, event, callback)
stopListening

object.off([event], [callback], [context])
once

object.stopListening([other], [event], [callback])
listenToOnce

object.once(event, callback, [context])
trigger

object.trigger(event, [*args])

object.listenToOnce(other, event, callback)

Models

MVC: Notify their observers about
state using the Observer pattern

Models represent your data

Each model represents a data type in your app, together with the logic surrounding it, like:

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persistence
conversions

validation
computed properties

access control

Models
You extend Backbone.Model with your domain-specific methods, and Model provides a basic set of
functionality for managing changes, like:

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getter and setter
id

constructor
REST-based persistence

Example of model
custom method

an attribute

event fired when
“color” changes

custom method
invocation

Model constructore and attributes
initialize()
it is triggered every time you create a new instance of a model
it works also for collections and views
it can take a JS object for setting also attributes
get() & set()
they are used to set and retrieve the value of certain attributes
defaults

a property named 'defaults' in your model declaration

Model persistence
Backbone.sync
is the function that Backbone calls every time it attempts to read or save a model

By default, it uses Ajax to make a REST-ish request to a server

Resources represented
as JSON strings

Sync signature
sync(method, model, [options])
method
the CRUD method ("create“, "read“, "update", or "delete")
model
the model (or collection) to be synced

example of overriden sync:
http://bit.ly/KWdxNN

options
success and error callbacks, and all other jQuery request options

Sync returns a jQuery XMLHttpRequest (jqXHR) object

It implements the Promise
interface

Sync usage
Normally you will not use the sync method directly, you will do it implicitly when you call one of these
methods

Model

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fetch: gets the most up-to-date values of the model instance

save: persists the model instance
destroy: deletes the model instance

Collection

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fetch: gets all the models of the collection from the server

create: creates a model, saves it to the server and adds it to the collection

Overriding sync
You can override it in order to use a different persistence strategy, such as:

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WebSockets
Local Storage
WebSQL

Backbone.sync is the default global function that all models use unless the models have a sync method
specifically set

Collections

MVC: Notify their observers about
state using the Observer pattern
(same as models)

Collections are ordered sets of models

You can:

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Any event that is triggered on a model in a collection will
also be triggered on the collection directly

bind change events to be notified when any model in the collection has been modified
listen for add and remove events
fetch the collection from the server (or other persistence layers)

find models or filter collections themeselves

The model attribute of a collection represents the kind of model that can be stored in it

Collection example

http://goo.gl/UOahsP

Views
Views represent and manage the visible parts of your application

MVC: observe models, and update
itself according to the state of the
models + manage user inputs (it’s a
controller, to this sense)

They are also used to

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listen to interaction events
and react accordingly

views can be rendered at any time, and inserted into the DOM

you get high-performance UI rendering
with as few reflows and repaints as possible

Interaction with the DOM
All views refer to a DOM element at all times, even if they are already in the page or not

this.el is a reference to the DOM element, it is created from:
tagName
for example body, ul, span, img
className

class name of some element within the DOM
id

id of an element within the DOM

If none of them is specified,
this.el is an empty <div>

Rendering the view
The render() method is used to update the this.el element with the new HTML

The default implementation of render() is a no-op
 you have to override it to update this.el with your HTML code

Backbone is agnostic with respect to your code in render(), however...

you are STRONGLY encouraged to use a
Javascript templating library here

View example

http://goo.gl/UOahsP

Interaction with the user
Events map
“event_name selector”: callback

Events callbacks

The router
Backbone.Router provides methods for routing client-side pages,
and connecting them to actions and events

At a minimum, a router is composed of two main parts:

routes
an hash that pairs routes to actions

actions
JS functions triggered when certain routes are navigated

Routing
Every router contains an hash that maps routes to functions on your router

URLs fragments can also contain dynamic data via Backbone-specific URL parts:
parameter (:param)
match a single URL component between slashes
splat (*fragment)
match any number of URL components

Routing
routes map

routing
functions

History
History serves as a global router to
1. handle hashchange events

Technically, it uses the HTML5 History
API to listen to to its job
For older browsers, it uses URL hash
fragments as fallback

2. match the appropriate route
3. trigger callbacks

You should never access it directly, you just need call Backbone.history.start() to begin
monitoring hashchange events, and dispatching routes in your app
Call Backbone.history.navigate(ROUTE_NAME, {trigger: true}); to activate a specific route
of the router

Classical workflow
1. You dig into JSON objects
2. Look up elements in the DOM
3. Update the HTML by hand

Backbone-based workflow
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You organize your interface into logical views backed by models

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Each view can be updated independently when the model changes,
without having to redraw the page
You can bind your view‘s render()
function to the model‘s "change”
event
 now everywhere that model
data is displayed in the UI, it is
always immediately up to date

Is Backbone real MVC?
Let’s look at the description of the Model-View-Presenter pattern on Wikipedia:
Model
an interface defining the data to be displayed or otherwise acted upon in the user interface
View
passive interface that displays data (the model) and routes user commands (events) to the
presenter to act upon that data
Presenter
acts upon the model and the view. It retrieves data from repositories (the model), and formats it
for display in the view

Roadmap
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Introduction

Backbone
Require JS

Handlebars
Conclusions

Require JS
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Why Require JS

Using modules
Defining modules

Configuring Require JS

Why Require JS
We are building apps, not website

We need well-specified and isolated JS files/modules

Code complexity grows as the app gets bigger
 we need some sort of #include/import/require
 ability to load nested dependencies

What we want to avoid
uncontrolled scripts

poor control flow understanding

Require JS
JavaScript and module loader
RequireJS is a JavaScript file file and module loader
Using a modular script loader like Require JS will improve the modularity of your code
 speed in implementing changes
 better undestanding of the code

Require JS allows modules to be loaded as fast as possible, even out of order, but evaluated in the
correct dependency order

Built on the Module Pattern

The module pattern
A JavaScript code module is some JavaScript code located in a registered location (e.g., a function)

All of the code that runs inside the function lives in a closure, which provides
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privacy

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state

throughout the lifetime of the module

Module example
Technically, it is simply a function that executes immediately

Module VS script files

VS

A module is different from a traditional script file in that it defines a well-scoped object that avoids
polluting the global namespace  its retained objects can be deleted by the GC
It can explicitly list its dependencies and get a handle on those dependencies without needing to refer to
global objects, but instead receive the dependencies as arguments to the function that defines the
module

Using modules
The main HTML:

main.js is the entry point of the app

Using modules
Required modules
The main JS file:

This function is called when all dependencies are loaded

If a required module calls define(), then this function is not fired
until its dependencies have been loaded

References to
required modules

Module without dependencies

Always one module per files

the simplest module can be a plain
collection of name/value pairs
module with initialization

Setup code

Public variables

The returned element can be any valid JS element
By convention I always return an object representing the module

Module with dependencies
Dependent module reference

Dependency
definition

This function is called when
zepto.js is loaded.
If zepto.js calls define(), then
this function is not fired until
also zepto’s dependencies
have loaded

Dependent module usage

Require JS under the hoods...
1. loads each dependency as a script tag, using head.appendChild() and waits for all dependencies to
load
2. computes the right order in which to call the functions that define the modules
3. calls the module definition functions of each dependency in the right order
1

4

3
jQuery

Backbone

MovieModel

5
MoviesCollection
2

7

SpinJS

main.js

6

MoviesView

Require refers to a global configuration options

It allows developers to:

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set the paths to all used frameworks in one place
use older frameworks as modules (shim)
define configuration params for the modules
etc.

paths to used frameworks

Shims for older
frameworks

Dependent module usage

Handlebars
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Why Handlebars

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Handlebars basics

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Usage with Backbone and Require JS

Why Handlebars
separate logic from from logic
We want to separate presentationpresentation
TRANSLATE TO: we don’t want to put any HTML element into JavaScript code

Imagine yourself trying to change how a movie should be rendered in
your app...

Example of template

A handlebars expression is

{{ something }}

Escape values

Handlebars HTML-escapes all the values returned by an {{expression}}
If you don't want Handlebars to escape a value, use the "triple-stash“  {{{ expression }}}

Populate your template
The recurrent process of obtaining a populated template is the following:
1. create the template T with its placeholders {{ - }}
2. compile the template into a JavaScript function t
3. create a context CT containing the actual values for placeholders

4. run the compiled template t(CT) to obtain the final HTML fragment

1. create the template
Templates are defined within a <script> tag or in external files

2. compile the template
Handlebars.compile is used to compile a template

Compiling = obtaining a JS object representing the template

3. create a context for the template
A context is a Javascript object used to populate a template

Here the keys of the object must match with the name of the placeholder to be populated

4. obtain the final HTML fragment
You have to execute a template with a context in order to get its corresponding HTML code

Expressions
The simplest expression is a simple identifier

This expression means "look up the username property in the current context"

Expressions with paths
Handlebars expressions can also be dot-separated paths

This expression means
"look up the user property in the current context,
then look up the username property in the result"

Helpers
Helpers are Javascript functions that return HTML code

You should return a Handlebars SafeString if you don't want it to be escaped by default

Calling helpers
A Handlebars helper call is a simple identifier, followed by zero or more parameters
Each parameter is a Handlebars expression
es.

{{ test user }}
In this case, test is the name of the Handlebars helper, and user is a parameter to the helper

Built-in helpers
with
It shifts the context for a section of a template
{ title: "My first post!",
author: { firstName: “Ivano", lastName: “Malavolta" }
}

<div class="entry“>
<h1>{{title}}</h1>
{{#with author}}
<h2>By {{firstName}} {{lastName}}</h2>
{{/with}}
</div>

<h1>My first post!</h1>
<h2>By Ivano Malavolta</h2>
</div>

Built-in helpers

Inside the block, you can use
this
to reference the element being iterated

each
To iterate over a list

{ people: [ “Ivano", “Andrea", “Paolo" ] }

<ul class="people_list">
{{#each people}}
<li>{{this}}</li>
{{/each}}
</ul>

<ul class="people_list">
<li>Ivano</li>
<li>Andrea</li>
<li>Paolo</li>
</ul>

Built-in helpers

The unless helper is the inverse of if

If / Else
It renders the block if its argument is not equal to false, undefined, null, []
{ title: "My first post!",
author: undefined }
}
<h1>{{title}}</h1>
{{#if author}}
<h2>By {{firstName}} {{lastName}}</h2>
{{#else}}
<h2>Unknown author</h1>
{{/if}}

<h1>My first post!</h1>
<h2>Unknown author</h2>
</div>

handlebars summary
Each Template can contain Expressions and Helpers operating on them
The main helpers are:
• with
• each
• if / else /unless
You can define your own Helpers that operate on expressions, they return HTML code

A template can be (pre)-compiled and must be executed with a context in order to return the
final HTML fragment

Usage with Backbone and Require JS
Templates can be seen as special modules

So we can have the following:
• a separate HTML file for each template
• a Backbone view can have a dependency to each template
• the template can be executed by using a JSON object of the Backbone model as context

Example

Dependency to template HTML file

It contains a string

Compiled template

Execution of the template

References

http://backbonejs.org
http://requirejs.org
http://handlebarsjs.com
https://github.com/iivanoo/cordovaboilerplate

Contact

Ivano Malavolta | DISIM
+ 39 380 70 21 600

iivanoo
ivano.malavolta@univaq.it
www.ivanomalavolta.com

Developing maintainable Cordova applications

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