This manual is for GNU LibreJS (version 6.0.10, 25 October 2015).
| • 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. | |
| • LibreJS Development Notes: | Documentation about the development of LibreJS itself. | |
| • 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. |
Next: Disclaimer, Previous: Top, Up: Top [Contents]
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"(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.
Next: Installation, Previous: Overview, Up: Top [Contents]
Next: How to Use, Previous: Disclaimer, Up: Top [Contents]
You can install LibreJS directly using a generated librejs.xpi file, or by building it from source.
After installing jpm, you should be able to use the make
command to build LibreJS from source.
After running make, a new file, librejs.xpi should be
generated. This is the file that can be installed in a Mozilla browser.
To install the add-on for all users, run:
sudo make install
or as root:
make install
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.
Next: JavaScript Detection, Previous: Installation, Up: Top [Contents]
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.
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, …)
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.
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 Control + Shift + A. Inside the add-on window, click on Extensions, and in the list, where you see LibreJS, click on the Preferences button. You will see an input field labeled Whitelist. In the field, enter comma-separated domain names. Do not enter the protocol. For instance to whitelist all the pages of http://www.gnu.org and https://gnu.org, enter ‘gnu.org’. To allow all subdomains from gnu.org, enter: ‘*.gnu.org’. This will match such sites as http://savannah.gnu.org and http://audio-video.gnu.org.
This specifies whether the complaint tab appears when a site is running nonfree JavaScript.
This option enables an info bar of realtime JavaScript analysis.
Configure the default subject used in complaint emails.
Configure the default body used in complaint emails.
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Obj.write, Obj.createElement, …).
In practice, the JavaScript code in your page may be found trivial by LibreJS if, as a whole:
<script> tag).
eval() method, use of square bracket
method calls, use of concatenation with certain constructs or method
calls, …).
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, …), or when a script is written with constructs that may do any of these.
For instance, if your page contains the following:
<script src="jquery.js"></script> <script> $.doSomething(); </script>
While $.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. $.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 .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 Content-Type in the response from the server. For
example, if you’re using JSON, set it to application/json.
This is because LibreJS alters the content of text/html
responses.
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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 <script> tags in HTML pages,
the license notice should appear once per page as a comment inside a
<script> tag, before all the code in that script. When the only
inline JavaScript code is within element attributes (onload,
onclick), place the license notice in an otherwise empty
<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.: <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:
magnet:?xt=urn:btih:8e4f440f4c65981c5bf93c76d35135ba5064d8b7&dn=apache-2.0.txt’
magnet:?xt=urn:btih:54fd2283f9dbdf29466d2df1a98bf8f65cafe314&dn=artistic-2.0.txt’
magnet:?xt=urn:btih:89a97c535628232f2f3888c2b7b8ffd4c078cec0&dn=Boost-1.0.txt’
magnet:?xt=urn:btih:c80d50af7d3db9be66a4d0a86db0286e4fd33292&dn=bsd-3-clause.txt’
magnet:?xt=urn:btih:84143bc45939fc8fa42921d619a95462c2031c5c&dn=cpal-1.0.txt’
magnet:?xt=urn:btih:90dc5c0be029de84e523b9b3922520e79e0e6f08&dn=cc0.txt’
magnet:?xt=urn:btih:4c6a2ad0018cd461e9b0fc44e1b340d2c1828b22&dn=epl-1.0.txt’
magnet:?xt=urn:btih:d3d9a9a6595521f9666a5e94cc830dab83b65699&dn=expat.txt’
magnet:?xt=urn:btih:87f119ba0b429ba17a44b4bffcab33165ebdacc0&dn=freebsd.txt’
magnet:?xt=urn:btih:cf05388f2679ee054f2beb29a391d25f4e673ac3&dn=gpl-2.0.txt’
magnet:?xt=urn:btih:1f739d935676111cfff4b4693e3816e664797050&dn=gpl-3.0.txt’
magnet:?xt=urn:btih:5de60da917303dbfad4f93fb1b985ced5a89eac2&dn=lgpl-2.1.txt’
magnet:?xt=urn:btih:0ef1b8170b3b615170ff270def6427c317705f85&dn=lgpl-3.0.txt’
magnet:?xt=urn:btih:0b31508aeb0634b347b8270c7bee4d411b5d4109&dn=agpl-3.0.txt’
magnet:?xt=urn:btih:b8999bbaf509c08d127678643c515b9ab0836bae&dn=ISC.txt’
magnet:?xt=urn:btih:3877d6d54b3accd4bc32f8a48bf32ebc0901502a&dn=mpl-2.0.txt’
magnet:?xt=urn:btih:e95b018ef3580986a04669f1b5879592219e2a7a&dn=public-domain.txt’
magnet:?xt=urn:btih:478974f4d41c3fa84c4befba25f283527fad107d&dn=upl-1.0.txt’
magnet:?xt=urn:btih:723febf9f6185544f57f0660a41489c7d6b4931b&dn=wtfpl.txt’
magnet:?xt=urn:btih:5305d91886084f776adcf57509a648432709a7c7&dn=x11.txt’
magnet:?xt=urn:btih:12f2ec9e8de2a3b0002a33d518d6010cc8ab2ae9&dn=xfree86.txt’
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 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: http://www.gnu.org/licenses/license-list.html
Next: LibreJS Development Notes, Previous: Free Licenses Detection, Up: Top [Contents]
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.
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:
<head> tag, it includes jQuery
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.
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: http://www.gnu.org/licenses/license-list.html
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:
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 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: https://www.gnu.org/software/librejs/free-your-javascript.html#step3 and here: https://www.gnu.org/licenses/javascript-labels.html.
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:
<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"
>GPL-3.0+</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>
The <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.
See a “Convention for releasing free JavaScript programs” in the JavaScript Trap http://www.gnu.org/philosophy/javascript-trap.html
Adding this notice will ensure LibreJS will find the JavaScript file to
be free. The @licstart and @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 <script> tags with on-page code and the inline
JavaScript (in event attributes such as onload, onclick, etc, …).
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 @licstart and @licend.
You should make only one @licstart @licend
comment in your page, since it pertains to the entire code on page
across all <script> tags and inline html attributes.
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: https://www.gnu.org/software/librejs/free-your-javascript.html
Next: Installation Requirements, Previous: Setting Your JavaScript Free, Up: Top [Contents]
Download jpm, then do something like this in the LibreJS
directory:
jpm run -b `which abrowser`
Uncomment lines 22 and 23 in lib/main.js to enable printing of
console.debug() statements.
Run the data/script_libraries/gethash.sh script, using the URL to a JavaScript file as the argument, then add the output of that command to data/script_libraries/script-libraries.json.
Update the version number in:
Then run ‘make info’ to build the docs with gendocs.sh.
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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.
LibreJS uses the Mozilla jpm tool, a set of utilities for
creating, testing, running and packaging Mozilla Jetpack Addons.
You do not need jpm to use the 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. If you would like to run the
tests for LibreJS or make changes to the source files, you
will need jpm as well. For the “make” command to work
properly, you must have the jpm command available on your system
from the command line.
You can find information on getting jpm at these links:
https://www.npmjs.com/package/jpm
https://developer.mozilla.org/en-US/Add-ons/SDK/Tutorials/Getting_Started_%28jpm%29
JPM is released under the Mozilla Public License 2.0.
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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 type and 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, …) and JavaScript do not fall through the cracks and get executed.
Next: GNU Free Documentation License, Previous: LibreJS Internals, Up: Top [Contents]
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:
@licstart and @licend. All
JavaScript is executed.
@licstart @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.)
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. http://fsf.org/ Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.
A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.
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The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.
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If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
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You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.
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You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”
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