\input texinfo @c -*-texinfo-*-
@c %**start of header
@setfilename librejs.info
@include version.texi
@settitle GNU LibreJS @value{VERSION}

@copying
This manual is for GNU LibreJS (version @value{VERSION}, @value{UPDATED}),
a GNU IceCat extension to detect and block nonfree nontrivial
JavaScript on webpages.

Copyright @copyright{} 2011 2012 2014 2015 Loic J. Duros

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled
``GNU Free Documentation License''.
@end quotation
@end copying

@dircategory GNUzilla
@direntry
* LibreJS: (librejs).               Detect nonfree nontrivial in GNU Icecat
@end direntry

@titlepage
@title GNU LibreJS
@subtitle for version @value{VERSION}, @value{UPDATED}
@author Loic J. Duros  (@email{librejs@@lduros.net})
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage


@contents


@node Top
@top LibreJS
This manual is for GNU LibreJS (version @value{VERSION}, @value{UPDATED}).

@menu
* Overview::                            General purpose and information.
* Disclaimer::                          Emphasize what LibreJS does and does not.
* Installation::                        Installing LibreJS from source. 
* How to Use::                          How to use LibreJS in IceCat.
* JavaScript Detection::                How LibreJS detects nontrivial Javascript.
* Free Licenses Detection::             List of licenses detected by LibreJS.
* Setting Your JavaScript Free::        Information for website owners/maintainers.
* Installation Requirements::           Requirements to build and install LibreJS.
* LibreJS Internals::                   How LibreJS works under the hood.
* Tests::                               Test LibreJS and better understand it.
* GNU Free Documentation License::      Copying and sharing this documentation.
@end menu

@node Overview
@chapter Overview

@cindex overview
GNU LibreJS ---an add-on for GNU IceCat and Mozilla Firefox--- detects
and blocks nonfree nontrivial JavaScript while allowing its execution on
pages containing code that is either trivial and/or free.

Many websites run nontrivial JavaScript on your computer. Some use it
for complex tasks; many use it gratuitously for minor jobs that could be
done easily with plain HTML.  Sometimes this JavaScript code is
malicious.  Either way, the JavaScript code is often nonfree.  For
explanation of the issue, see "The JavaScript
Trap"(@url{http://www.gnu.org/philosophy/javascript-trap.html}).

If you care about freedom in your computing, and don't wish to let all
and sundry make you run nonfree programs, now you can prevent it by
using LibreJS.


@node Disclaimer
@chapter Disclaimer

@cindex disclaimer

@itemize @bullet
@item
LibreJS is not a security tool. Its goal is to detect nonfree nontrivial
JavaScript, and it currently does not detect whether free or trivial
code is malicious or not. Other free Mozilla extensions and add-ons may
be available for this purpose.

@item
LibreJS is always a work in progress. If you find a bug, please report
it to @email{bug-librejs@@gnu.org}.

@end itemize

@node Installation
@chapter Installation
@cindex Installation

You can install LibreJS directly using a generated @file{librejs.xpi}
file, or by building it from source.


@section Building the Package
After enabling the Add-on SDK, you should be able to use the @code{make}
command to build LibreJS from source.

After running @code{make}, a new file, @file{librejs.xpi} should be
generated. This is the file that can be installed in a Mozilla browser. 

@section Installing LibreJS
To install the add-on for all users, run:
@example 
sudo make install
@end example

or as root:
@example
make install
@end example

Next time you open a Mozilla-browser as a user of your system, you
should be notified that a new add-on (in this case, LibreJS) as been
installed and whether to allow it to run or not.

@node How to Use
@chapter How to Use

@section LibreJS in action

After installing the add-on, you will see the LibreJS widget in the
add-on bar at the bottom of the browser window.  After loading a page,
left-click on the widget to view the deactivated JavaScript code from
the page (both on page and external) and, if applicable, the scripts
that were accepted.

@section Complaint Feature

It is very important to complain when a site has nonfree JavaScript
code, especially if it won't work without that code.  LibreJS makes it
easy to complain by heuristically finding where to send the complaint.

When nonfree/nontrivial code is detected in a page, LibreJS attempts to
find a relevant contact link or email for the website you are
visiting. In order to do so, it will attempt to visit a few links from
the current page (for instance, a link labeled ``contact'' on the same
domain as the current page, @dots{})

LibreJS detects contact pages, email addresses that are likely to be
owned by the maintainer of the site, Twitter and identi.ca links, and
phone numbers.

After LibreJS detects any of the above, a ``Complain'' tab will appear
on the right of your web browser. When you click on this tab, a large
panel will appear with contact information. Ideally, at the top you will
find the email address of the maintainer, labeled as the ``Email you
should use''.

When you complain to the website for their nonfree nontrivial
JavaScript, provide them with the link to the JavaScript Trap essay so
that they can get more information on what the issue is and how they can
solve it on their own site.

LibreJS includes a default subject line and body for the complaint email,
with a link to the JavaScript Trap essay. This can be configured in the
LibreJS add-on preferences in your web browser.


@section Options

@table @dfn
@item Whitelist
LibreJS lets you whitelist domain names and subdomains to bypass the
regular JavaScript check. This might be useful, for example, if you are
running your own code in a local web server. In order to add a
whitelisted domain or url, go to Tools >> Add-ons, or press @kbd{Control
+ Shift + A}. Inside the add-on window, click on @dfn{Extensions}, and in
the list, where you see LibreJS, click on the @dfn{Preferences} button.
You will see an input field labeled @dfn{Whitelist}. In the field,
enter comma-separated domain names. Do not enter the protocol. For
instance to whitelist all the pages of @url{http://www.gnu.org} and
@url{https://gnu.org}, enter @samp{gnu.org}. To allow all subdomains from
gnu.org, enter: @samp{*.gnu.org}. This will match such sites as
@url{http://savannah.gnu.org} and @url{http://audio-video.gnu.org}.

@item Complaint tab
This specifies whether the complaint tab appears when a site is running
nonfree JavaScript.

@item Display notifications of JavaScript analysis
This option enables an info bar of realtime JavaScript analysis.

@item Complaint email subject
Configure the default subject used in complaint emails.

@item Complaint email body
Configure the default body used in complaint emails.
@end table

@node JavaScript Detection
@chapter JavaScript Detection
@cindex javascript

@itemize
LibreJS considers JavaScript on a page nontrivial if any of the
following are true:

@item
It makes an AJAX request or is loaded along with scripts that make
an AJAX request,

@item
It loads external scripts dynamically or is loaded along with
scripts that do,

@item
It defines functions or methods and either loads an external script
(from HTML) or is loaded as one,

@item
It uses dynamic JavaScript constructs that are difficult to analyze
without interpreting the program or is loaded along with scripts
that use such constructs. These constructs are:
@itemize
@item
Using the eval function
@item
Calling methods with the square bracket notation
@item
Using any other construct than a string literal with certain methods
(@code{Obj.write}, @code{Obj.createElement}, @dots{}).
@end itemize
@end itemize

In practice, the JavaScript code in your page may be found trivial by
LibreJS if, as a whole:
@itemize @bullet

@item
It does not define functions and it does not load external scripts
(with the HTML src attribute in a @code{<script>} tag).

@item
It does not make AJAX calls.

@item
It does not load external scripts with dynamic constructs.

@item
It does not use constructs that may be used to do any of the above in
a non-obvious way (use of the @code{eval()} method, use of square bracket
method calls, use of concatenation with certain constructs or method
calls, @dots{}).

@end itemize

However, in some instances, you may be required by LibreJS to add a
stylized comment to JavaScript code that may be otherwise trivial.

When an external file defines a function, it becomes available
to all other external scripts. That is the case if another script
defines a function that makes AJAX calls, when an external script
loads other scripts dynamically (which in turn could also make AJAX
calls, @dots{}), or when a script is written with constructs that may do
any of these.

For instance, if your page contains the following:
@example
<script src="jquery.js"></script>
<script>
$.doSomething();
</script>
@end example

While @code{$.doSomething();} may seem trivial, you will nevertheless
have to add a stylized license comment on your main HTML page because
the external script (in this case jQuery) has been found to define
methods that make AJAX calls. @code{$.doSomething()} might make an AJAX call,
and LibreJS does not check for that.  The rule of thumb is that when you
use a library or code that handles AJAX, JSON, JSONP, the loading of
scripts dynamically, you should have license mentions for all your
JavaScript files and for your main page regardless. In practice this is
a case that happens very often with code that uses libraries.

In practice also, the JavaScript code in an external file (an external
@file{.js} file loaded on your page) may be found trivial if it does not
define functions/methods.

And in the same manner it will be considered nontrivial if AJAX calls,
dynamic script loading, or non-obvious dynamic JavaScript constructs
are used in another script.

If your JavaScript code makes AJAX requests, it's important to get an
accurate @dfn{Content-Type} in the response from the server. For
example, if you're using JSON, set it to @code{application/json}.
This is because LibreJS alters the content of @code{text/html}
responses.

@node Free Licenses Detection
@chapter Free Licenses Detection
@cindex freelicenses

@section Detected Free Licenses

In order for a file to be detected as free, the license notice should
appear in a JavaScript file above all code, at the very top of the file.

For inline JavaScript code inside @code{<script>} tags in HTML pages,
the license notice should appear once per page as a comment inside a
@code{<script>} tag, before all the code in that script. When the only
inline JavaScript code is within element attributes (@code{onload},
@code{onclick}), place the license notice in an otherwise empty
@code{<script>} at the top of the page. This is sometimes needed when an
external script performs AJAX calls or embeds scripts dynamically, and
the only inline JavaScript is an event attribute making a method call,
e.g.: @code{<body onload="methodCall('remote-data.xml');">}

When people speak of the ``MIT license'' they mean either the X11 license
or the Expat license.  Please see which license the code uses, and label
it accordingly.

Currently LibreJS checks for the following licenses:

@itemize @bullet

@item
Apache License, Version 2.0
@itemize @bullet
@item
Identifier: @samp{Apache-2.0}
@item
URL: @url{http://www.apache.org/licenses/LICENSE-2.0}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:8e4f440f4c65981c5bf93c76d35135ba5064d8b7&dn=apache-2.0.txt}
@end itemize

@item
Artistic License 2.0
@itemize @bullet
@item
URL: @url{http://www.perlfoundation.org/artistic_license_2_0}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:54fd2283f9dbdf29466d2df1a98bf8f65cafe314&dn=artistic-2.0.txt}
@end itemize

@item
Boost Software License
@itemize @bullet
@item
URL: @url{http://www.boost.org/LICENSE_1_0.txt}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:89a97c535628232f2f3888c2b7b8ffd4c078cec0&dn=Boost-1.0.txt}
@end itemize

@item
BSD 3-Clause License
@itemize @bullet
@item
URL: @url{http://opensource.org/licenses/BSD-3-Clause}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:c80d50af7d3db9be66a4d0a86db0286e4fd33292&dn=bsd-3-clause.txt}
@end itemize

@item
CPAL 1.0
@itemize @bullet
@item
Identifier: @samp{CPAL-1.0}
@item
URL: @url{http://opensource.org/licenses/cpal_1.0}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:84143bc45939fc8fa42921d619a95462c2031c5c&dn=cpal-1.0.txt}
@end itemize

@item
Creative Commons CC0 1.0 Universal
@itemize @bullet
@item
Identifier: @samp{CC0-1.0}
@item
URL: @url{http://creativecommons.org/publicdomain/zero/1.0/legalcode}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:90dc5c0be029de84e523b9b3922520e79e0e6f08&dn=cc0.txt}
@end itemize

@item
Eclipse Public License 1.0
@itemize @bullet
@item
Identifier: @samp{EPL-1.0}
@item
URL: @url{http://www.eclipse.org/legal/epl-v10.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:4c6a2ad0018cd461e9b0fc44e1b340d2c1828b22&dn=epl-1.0.txt}
@end itemize

@item
Expat License (sometimes called the MIT license)
@itemize @bullet
@item
Identifier: @samp{Expat}
@item
URL: @url{http://www.jclark.com/xml/copying.txt}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:d3d9a9a6595521f9666a5e94cc830dab83b65699&dn=expat.txt}
@end itemize

@item
FreeBSD License
@itemize @bullet
@item
URL: @url{http://www.freebsd.org/copyright/freebsd-license.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:87f119ba0b429ba17a44b4bffcab33165ebdacc0&dn=freebsd.txt}
@end itemize

@item
GNU General Public License (GPL) version 2
@itemize @bullet
@item
Identifier: @samp{GNU-GPL-2.0}
@item
URL: @url{http://www.gnu.org/licenses/gpl-2.0.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:cf05388f2679ee054f2beb29a391d25f4e673ac3&dn=gpl-2.0.txt}
@end itemize

@item
GNU General Public License (GPL) version 3
@itemize @bullet
@item
Identifier: @samp{GNU-GPL-3.0}
@item
URL: @url{http://www.gnu.org/licenses/gpl-3.0.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:1f739d935676111cfff4b4693e3816e664797050&dn=gpl-3.0.txt}
@end itemize

@item
GNU Lesser General Public License, version 2.1
@itemize @bullet
@item
Identifier: @samp{GNU-LGPL-2.1}
@item
URL: @url{http://www.gnu.org/licenses/lgpl-2.1.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:5de60da917303dbfad4f93fb1b985ced5a89eac2&dn=lgpl-2.1.txt}
@end itemize

@item
GNU Lesser General Public License, version 3
@itemize @bullet
@item
Identifier: @samp{GNU-LGPL-3.0}
@item
URL: @url{http://www.gnu.org/licenses/lgpl-3.0.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:0ef1b8170b3b615170ff270def6427c317705f85&dn=lgpl-3.0.txt}
@end itemize

@item
GNU Affero General Public License, version 3
@itemize @bullet
@item
Identifier: @samp{GNU-AGPL-3.0}
@item
URL: @url{http://www.gnu.org/licenses/agpl-3.0.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:0b31508aeb0634b347b8270c7bee4d411b5d4109&dn=agpl-3.0.txt}
@end itemize

@item
The ISC License
@itemize @bullet
@item
URL: @url{https://www.isc.org/downloads/software-support-policy/isc-license/}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:b8999bbaf509c08d127678643c515b9ab0836bae&dn=ISC.txt}
@end itemize

@item
Mozilla Public License 2.0
@itemize @bullet
@item
Identifier: @samp{MPL-2.0}
@item
URL: @url{http://www.mozilla.org/MPL/2.0}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:3877d6d54b3accd4bc32f8a48bf32ebc0901502a&dn=mpl-2.0.txt}
@end itemize

@item
Public Domain
@itemize @bullet
@item
Public domain is not a license (see
@url{https://www.gnu.org/licenses/license-list.html#PublicDomain}). If
you want to release your work to the public domain, the FSF recommends
using CC0.
@item
Magnet Link: @indicateurl{magnet:?xt=urn:btih:e95b018ef3580986a04669f1b5879592219e2a7a&dn=public-domain.txt}
@end itemize

@item
WTFPL
@itemize @bullet
@item
Identifier: @samp{WTFPL}
@item
URL: @url{http://www.wtfpl.net/txt/copying/}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:723febf9f6185544f57f0660a41489c7d6b4931b&dn=wtfpl.txt}
@end itemize

@item
X11 License
@itemize @bullet
@item
URL: @url{http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:5305d91886084f776adcf57509a648432709a7c7&dn=x11.txt}
@end itemize

@item
XFree86 License
@itemize @bullet
@item
Identifier: @samp{Modified-BSD}
@item
URLs:
@url{http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3}
@url{http://www.xfree86.org/current/LICENSE4.html}
@item
Magnet link: @indicateurl{magnet:?xt=urn:btih:12f2ec9e8de2a3b0002a33d518d6010cc8ab2ae9&dn=xfree86.txt}
@end itemize

@end itemize

@section Undetected Free Licenses
If you are using a free license that isn't detected by LibreJS and isn't
listed in the previous section, please send a message to
@email{bug-librejs@@gnu.org} regarding this license, where code released under
this license can be found, and where to find the license text and
information.

Many free licenses are listed in this page:
@url{http://www.gnu.org/licenses/license-list.html}


@node Setting Your JavaScript Free
@chapter Setting Your JavaScript Free

The first step is releasing your JavaScript under a free license. If
you are already using a free library, or you're not using any
third-party libraries, it might only take a few minutes.

All JavaScript code on a web page (inline, on-page, and external) shares
a common scope. Thus, code is generally either rejected or accepted as a
whole by LibreJS. If some JavaScript code is found to be nontrivial and
nonfree, then most of the time, all the the rest is discarded as well.

On your website, take a look at your HTML source. You can identify
distinct pieces of JavaScript that might be free and some other that are
nonfree.

@emph{Tip}: By running LibreJS on your page, you will get a list of all the
JavaScript that was blocked. This gives you an overview of the
JavaScript in your page.

Imagine a page that contains several pieces of JavaScript from various
sources:
@itemize @bullet
@item
On top, within the @code{<head>} tag, it includes jQuery

@item
Then, some JavaScript code that you have written

@item
At the bottom, a JavaScript-based Facebook widget

@item
Also, there's some analytics tracking code
@end itemize


@table @dfn
@item JavaScript that is already free
First, you must ensure that the library is free. If the file contains
a copyright and a license notice, you won't need to look any further.
But if there's no mention of the license, or if it's too brief, you'll
have to look for a COPYING or LICENSE file within the original library's
source package, or on the library's official website.

@item Your own JavaScript
The free license given to your code should be compatible with the rest
of the JavaScript on a page. A good way to check is to read up on
them: @url{http://www.gnu.org/licenses/license-list.html}

@item Nonfree JavaScript
This might be the case with an analytics tracker, social media
widgets, and code that runs ads. Removing these pieces of code from your
site is required to have the rest accepted as free. There are
often alternatives to nonfree libraries or to third-party services:

@itemize @bullet

@item
If you have used nonfree third-party code as the base to write your own
code, try to find a free alternative.

@item
If you're using a third-party service such as an analytics service,
replace it with a free alternative like Piwik.

@item
If you can't find free JavaScript that has already been developed,
write it yourself! Who knows, your own solution might be the start of
a brilliant project!
@end itemize

@end table

@section JavaScript Web Labels
One way to make your website work with LibreJS is by defining a
JavaScript Web Labels table.

A JavaScript Web Labels table is informative to both site visitors and
the LibreJS program. You make a Web Labels table on a new HTML page
that's linked to from your main page. The table lists each of your
site's JavaScript files, that file's corresponding human-readable source
file, and the canonical url of its free license.

When using a JavaScript Web Labels table for your own files, it's
important to put a copying permission statement at the top of each source
file listed in right-most column of the Web Labels table. For info on how
properly release your code as free software, see
@url{https://www.gnu.org/licenses/gpl-howto.html}. Future versions of
LibreJS will require a copying permission statement or other license
notice for source files listed in a Web Labels table.

More information on JavaScript Web Labels is detailed here:
@url{https://www.gnu.org/software/librejs/free-your-javascript.html#step3}
and here:
@url{https://www.gnu.org/licenses/javascript-labels.html}.

@subsection Specifying multiple licenses for a single JavaScript file

If you compile or concatenate your JavaScript into a single file, the
source files you're combining may be released under different licenses.
You can specify multiple licenses for the file in a JavaScript Web Labels
table, like this:

@verbatim
<table id="jslicense-labels1">
    <tr>
        <td><a href="all.min.js">all.min.js</a></td>
        <td>
            <a href="http://www.gnu.org/licenses/gpl-3.0.html"
                >GNU-GPL-3.0-or-later</a>
            <br />
            <a href="http://www.apache.org/licenses/LICENSE-2.0"
                >Apache-2.0</a>
        </td>
        <td>
            <a href="gpl-script.js">gpl-script.js</a>
            <br />
            <a href="apache-script.js">apache-script.js</a>
        </td>
    </tr>
</table>
@end verbatim

The @code{<br />} tags just make the table more understandable when
looking at the rendered version of it on the license page. They aren't
required by LibreJS.

If all the licenses contained in the second column are recognized by
LibreJS to be free licenses, then LibreJS will allow the file in the
first column to be run.

@section Adding a stylized comment in your JavaScript files and on your page
See a ``Convention for releasing free JavaScript programs'' in the
JavaScript Trap @url{http://www.gnu.org/philosophy/javascript-trap.html}

Adding this notice will ensure LibreJS will find the JavaScript file to
be free. The @code{@@licstart} and @code{@@licend} lines at the
beginning and end of the stylized comment are necessary to make a clear
statement that the _entire code_ in the file is free. This means that
you must ensure that no nonfree code was carelessly appended at the end
of the file.

In the main HTML page, the license notice covers JavaScript contained
in all @code{<script>} tags with on-page code and the inline
JavaScript (in event attributes such as onload, onclick, etc, @dots{}).
Since external files have their own stylized comment, they are
not covered by the notice in the main HTML page. Make sure to identify
all the licenses available. LibreJS will only ensure it matches a
notice of an allowed license once, so the order does not matter, but
the responsibility is on you to make sure all code is under the free
licenses mentioned between @code{@@licstart} and @code{@@licend}.

You should make @emph{only} one @code{@@licstart} @code{@@licend}
comment in your page, since it pertains to the entire code on page
across all @code{<script>} tags and inline html attributes.

@unnumbered
When you use the JavaScript Web Labels method, you should still include a
license notice at the top of each of your source files. This ensures that
if someone copies the file and uses it for something else, the license
remains intact.
    
For more info on making your JavaScript LibreJS-compliant, see this web
page: @url{https://www.gnu.org/software/librejs/free-your-javascript.html}

@node Installation Requirements
@appendix Installation Requirements


@appendixsec Mozilla Browser

You will need one of the many flavors of the Mozilla browser to use
LibreJS. It can be installed on the following:

GNU IceCat,  Mozilla Firefox, Trisquel Abrowser, Debian Iceweasel.

LibreJS works on these browsers starting from version 29. We
recommend that you use the latest version of your Mozilla browser.
LibreJS has been tested extensively on multiple GNU/Linux distributions,
but it is compatible any operating system as long as you're using a
compatible Mozilla browser.

@appendixsec Mozilla's Add-on SDK
LibreJS uses the Mozilla Add-on SDK (Software Development Kit), a
set of APIs and tools to create add-ons for Mozilla browsers.

You do not need the Add-on SDK to use LibreJS xpi file or to install it
using the packaged version, but it is required in order to package the
LibreJS source code into an xpi file using @code{make}. If you would like
to run the tests for LibreJS or make changes to the source files, you
will need the Add-on SDK as well. For the ``make'' command to work
properly, you must have the @code{cfx} command available on your system
from the command line.

The latest tarball for the Add-on SDK is available at:

@url{https://ftp.mozilla.org/pub/mozilla.org/labs/jetpack/jetpack-sdk-latest.tar.gz}

Instructions on how to get it working are available here:

@url{https://addons.mozilla.org/en-US/developers/docs/sdk/latest/dev-guide/tutorials/installation.html}

In order to use @code{make} with LibreJS source, however, it is ideal to
have @code{cfx} available at all times and for all users.

An easy way to do this is to extract the contents of the tarball and to
place the files inside @file{/usr/lib/addon-sdk} and then creating a
symbolic link in @file{/usr/bin}, as follows:

@example 
sudo ln -s /usr/lib/addon-sdk/bin/cfx /usr/bin/cfx
@end example

The @code{cfx} command will then be available to all users.

The Add-on SDK is released under the Mozilla Public License 2.0.

@node LibreJS Internals
@appendix LibreJS Internals

LibreJS intercepts HTTP responses and rewrites their contents after
analyzing JavaScript within them. It does not remove script nodes and
attributes from the page, but instead ``deactivates'' them by modifying
the @code{type} and @code{src} attributes on script elements and by
moving the contents of inline JavaScript attributes such as onClick
into harmless attributes.

LibreJS detects the most common cases using the HTTP response method
described above, but in extremely rare cases, or when running code
locally, LibreJS cannot detect JavaScript during the response stage.

To remedy this issue, and as a final safeguard, LibreJS takes a look
at the scripts that are about to be executed while the browser engine is
parsing the page. If the script is not found in a list of accepted
scripts populated earlier, the execution will be prevented. This is to
ensure content types that are not regular HTML (binhex with HTML in it,
@dots{}) and JavaScript do not fall through the cracks and get executed.

@node Tests
@appendix Tests


In order to better understand how LibreJS works, you can try to visit
these pages with LibreJS installed and enabled and see how they are
being processed:

@itemize @bullet

@item
@url{http://lduros.net/assets/librejs/tests/trivial-inline-trivial-external/}
This page contains trivial on-page JavaScript code, and an external
script that contains trivial JavaScript code.  Therefore, all JavaScript
is being executed.


@item
@url{http://lduros.net/assets/librejs/tests/trivial-inline-nontrivial-external/}
The on-page script here is trivial and uses a built-in method, but the
external script in this page is nontrivial (defines a function.)  The
external script is blocked, the inline script is executed.

@item
@url{http://lduros.net/assets/librejs/tests/nontrivial-inline-trivial-external/}
This page contains nontrivial code on page, and trivial code in its
external page.  All JavaScript is @emph{removed} from the page, and the
external script is never analyzed, since the nontrivial conditions are
already met in the page.

@item
@url{http://lduros.net/assets/librejs/tests/free-inline-free-external/}
This page contains free on-page (GPL 3) JavaScript, and free external
Javascript. Therefore all JavaScript is being executed.

@item
@url{http://lduros.net/assets/librejs/tests/free-inline-nonfree-nontrivial-external/}
This page contains free on-page JavaScript. The external script contains
nonfree nontrivial JavaScript (AJAX request). The free code that is
inline is executed, but the external file is blocked.

@item
@url{http://lduros.net/assets/librejs/tests/intrinsec-event/} This page
contains trivial on-page code, with an intrinsic event in an html
attribute (onload).  All JavaScript is being executed.

@item
@url{http://lduros.net/assets/librejs/tests/trivial-inline-free-external-defines-function/}
This page contains on-page trivial JavaScript (only makes a window alert
and loads an external script using the html <script> tag with the src
attribute. The external script is free (GPL v3), and since it is only
nontrivial because it defines a function, the on-page trivial code is
allowed to use it.  All JavaScript is being executed.

@item
@url{http://lduros.net/assets/librejs/tests/trivial-inline-free-external-writes-script/}
This page contains trivial on-page JavaScript code, and loads an
external script that is free. Since no function is defined, the external
script is being analyzed. The external script is free. Trivial here is
not allowed because the external script, although free, writes a
script. The inline trivial script should also have a free license notice
for it to be interpreted.

@item
@url{http://lduros.net/assets/librejs/tests/shelltypist/demo/real-life-example-with-jquery-free.html}
This is a real-life example of a small jQuery plugin. The on-page
JavaScript code has a free license. The jQuery external file has a free
licensed. The shelltypist.js file has a free license as well. All
licenses are defined between @code{@@licstart} and @code{@@licend}. All
JavaScript is executed.

@item
@url{http://lduros.net/assets/librejs/tests/shelltypist/demo/same-page-without-free-license.html}
This is the same page than the previous example, except it does not have
a free license for the main HTML page on-page script. While the actual
code there is trivial, since jQuery defines methods that make use of
AJAX, trivial code is not allowed, and no JavaScript is executed.

@item
@url{http://lduros.net/assets/librejs/tests/test-labels/} This page
contains JavaScript (jQuery minified) that does not have proper license
information in the file, as it has no @code{@@licstart} @code{@@licend}
comment. It would be considered nonfree, however, the page itself uses
the JavaScript Web Labels method. On the page itself, you will find a
link labeled ``JavaScript License Information'', which leads to a page
that contains a properly formatted table with the required data on the
external JavaScript file. LibreJS visits this link and determines the
version of jQuery linked from the original page is the one listed there,
and flags it as free. All JavaScript is executed (and the title should
turn green.)

@end itemize


@node GNU Free Documentation License
@appendix GNU Free Documentation License

@include fdl.texi


@bye
