Handlebars & Require JS

Gran Sasso Science Institute
Ivano Malavolta
Handlebars
& Require JS

Roadmap
•  Introduction
•  Require JS
•  Handlebars
•  Conclusions

Some technical advices from a real project...

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

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 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
JavaScript ﬁle and module loader

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
•  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
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
VS

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

Module without dependencies Always one module per ﬁle
Public variables
Setup code
the simplest module can be a plain
collection 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 dependencies
Dependency
definition
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

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 older
frameworks
paths to used frameworks
Dependent module
usage

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...

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
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
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>

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}}

{
title:
"My
first
post!",

author:
undefined
}

}

<div
class="entry“>

<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 |
Gran Sasso Science Institute
iivanoo
ivano.malavolta@gssi.infn.it
www.ivanomalavolta.com

Handlebars & Require JS

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