Ivano Malavolta

Handlebars & Require JS

How you structure your applications

MVC framework for giving structure

File and module loader for code modularization

Templating engine for separation of concerns

How you structure your applications

Roadmap

• Require JS

• Handlebars

• Conclusions

Require JS

• Why Require JS

• Using modules

• Defining modules

• Configuring Require JS

Why Require JS

We are building apps, not websites

We need well-specified and isolated JS files/modules

Code complexity grows as the app gets bigger

à we need some sort of #include/import/require

à ability to load nested dependencies

What we want to avoid

uncontrolled scripts

poor control flow understanding

RequireJS

RequireJS is a JavaScript file and module loader

Using a modular script loader like RequireJS will improve the modularity of your code

à speed in implementing changes

à better understanding 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

JavaScript file and module loader

The module pattern

A JavaScript code module is some JavaScript code located in a function

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

• privacy

• state

throughout the lifetime of the module

Module example

Technically, it is simply a function that executes immediately

Module VS script files

A module is different from a traditional script file in that it defines a well-scoped object that avoids polluting the global namespace à its retained objects can be deleted by the GC

VS

Require JS

• Why Require JS

• Using modules

• Defining modules

• Configuring Require JS

Using modules

main.js is the entry point of the app

The main HTML:

The main JS file:

Using modules

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

Required modules References to required modules

Require JS

• Why Require JS

• Using modules

• Defining modules

• Configuring Require JS

Module without dependencies Always one module per file

Public variables

Setup code

the simplest module can be a plaincollection of name/value pairs

module with initialization

The returned element can be any valid JS element

By convention I always return an object representing the module

Module with dependenciesDependencydefinition

Dependent module reference

Dependent module usage

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

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

main.js

jQuery Backbone

SpinJS

MoviesCollection

MovieModel

MoviesView

1

2

3 4

5

67

Require JS

• Why Require JS

• Using modules

• Defining modules

• Configuring Require JS

Configuring Require JS

Require refers to a global configuration options

It allows developers to:

• set the paths to all used frameworks in one place

• use older frameworks as modules (shim)

• define configuration params for the modules

• etc.

Configuring Require JS

Shims for olderframeworks

paths to used frameworks

Dependent module usage

Roadmap

• Require JS

• Handlebars

• Conclusions

Handlebars

• Why Handlebars

• Handlebars basics

• Usage with Backbone and Require JS

Why Handlebars

We want to separate presentation from logic

TRANSLATE TO: we don’t want to put any HTML element into JavaScript code

separate logic from presentation

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

Handlebars

• Why Handlebars

• Handlebars basics

• Usage with Backbone and Require JS

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“ à {{{ 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 function 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 placeholders 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 of the user"

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

An 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

To iterate over a list

each

Inside the block, you can use this

to reference the element being iterated

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

<li>{{this}}</li>{{/each}}

</ul>

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

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

</ul>

Built-in helpers

It renders the block if its argument is not equal to false, undefined, null, []

If / Else

The unless helper is the inverse of if

<div class="entry“><h1>{{title}}</h1>{{#if author}}

<h2>By {{firstName}} {{lastName}}</h2>{{#else}}

<h2>Unknown author</h1>{{/if}}</div>

{ title: "My first post!", author: undefined }

}

<div class="entry“><h1>My first post!</h1><h2>Unknown author</h2></div>

Built-in helpers

It shifts the context for a section of a template

with

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

<h2>By {{firstName}} {{lastName}}</h2>{{/with}}</div>

{ title: "My first post!", author: { firstName: “Ivano", lastName: “Malavolta" }

}

<div class="entry“><h1>My first post!</h1><h2>By Ivano Malavolta</h2></div>

handlebars summary

Each Template can contain Expressions and Helpers operating on them

The main helpers are: • each• if / else /unless• with

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

Handlebars

• Why Handlebars

• Handlebars basics

• Usage with Backbone and Require JS

Usage with Backbone and Require JS

Templates can be seen as special modules

So we can have the following:

1. a separate HTML file for each template

2. a Backbone view can have a dependency to each template

3. 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.orghttp://requirejs.org

http://handlebarsjs.comhttps://github.com/iivanoo/cordovaboilerplate

LAB

1. Integrate everything with the Cordova Boilerplate

• http://github.com/iivanoo/cordovaboilerplate

2. Define all Backbone’s objects as Require modules with dependencies

3. Move out all the HTML code you had in the JavaScript code into Handlebars templates

Contact Ivano Malavolta

iivanoo

ivano.malavolta@gssi.infn.it

www.ivanomalavolta.com