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<title>The JavaScript Trap</title> 
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<h2>The JavaScript Trap</h2>

<p>by

 <a href="http://www.stallman.org/">Richard Stallman</a></p> 

<p><strong>You may be running nonfree programs on your computer every
day without realizing it—through your web browser.</strong></p>



<p>In the free software community, the idea that
 nonfree programs
mistreat their users  is familiar.  Some of us refuse entirely to
install
 proprietary software, and many  others consider nonfreedom  a strike against the program.  Many
 users are aware that this issue applies to the plug-ins that
browsers offer to install, since they can be free or nonfree.</p>

<p>But 
browsers run other nonfree programs which they don't ask you
about  or
even tell you about—programs that web pages contain or link to.
These programs are most often written in JavaScript, though other
languages are also used.</p>

<p>JavaScript (officially called ECMAScript, but few use that name)
was once used for minor frills in web pages, such as cute but
inessential navigation and display features.  It was acceptable to
consider these as mere extensions of HTML markup, rather than as true software; they
did not constitute a significant
 issue.</p>

<p>Many

 sites still use JavaScript that way, but some  use it for major
programs that do large jobs.  For instance, Google Docs tries to download
 into your machine  a JavaScript program which measures half a
megabyte, in a compacted form that we could call Obfuscript because it has no
comments  and hardly any whitespace,  and  the method names are one
letter long.   The source code of a program is  the preferred form for
modifying it; the compacted
 code is not  source code, and  the real source code of this program  is
not available to the user.</p> 

<p>Browsers don't normally tell you when they load JavaScript
programs.  Some browsers have a way to turn off JavaScript entirely,
but even if you're aware of this issue, it would take you considerable
trouble to identify the nontrivial nonfree programs and block them.
However, even in the free software community most users are not aware
of this issue; the browsers' silence tends to conceal it.</p>

<p>It

 is possible to release a JavaScript program as free software, by
distributing the source code under a free software license.  If the
program is self-contained—if its functioning and purpose are
independent of the page it came in—that is fine; you can copy it
to a file on your machine, modify it, and visit that file with a
browser to run it.  But that is an unusual case.</p>

<p>In   the usual case,  JavaScript programs are meant  to work with a
particular page or site, and the page or site depends on them to
function.

Then another problem arises: even if the program's source
is available, browsers do not offer a way to run your modified version
instead of the original when visiting that page or site.  The effect
is comparable to tivoization, although in principle not quite so hard
to overcome.</p>

<p>JavaScript is not the only language web sites use for programs sent
to the user.  Flash supports  programming through an extended variant
of JavaScript; if we ever have  a sufficiently complete free Flash
player, we will need to deal with the issue  of nonfree Flash programs.  Silverlight
seems likely to create a problem similar to Flash, except worse, since
Microsoft uses it as a platform for nonfree codecs.  A free
replacement for Silverlight does not do the job  for the
free world unless it normally comes with free replacement codecs.</p>

<p>Java applets also run in the browser, and raise similar issues.  In
general, any sort of applet system poses this sort of problem.  Having
a free execution environment for an applet only brings us far enough
to encounter the problem.</p>

<p>It is theoretically possible to program in HTML and CSS, but in
practice this capability is limited and inconvenient; merely to make
it do something is an impressive hack.  Such programs ought to be
free, but CSS is not a serious problem for users' freedom as of
2016.</p>


<p>A strong movement has developed that calls for web sites to
communicate only through formats and protocols that are free (some say
"open");
 that is to say, whose documentation is published and which
anyone is free to implement.  With   the presence of  programs
in web
pages,  that criterion is necessary, but not sufficient.  JavaScript 
itself, as a format, is free, and use of JavaScript in a web site is
not necessarily bad.  However, as we've seen above, it also isn't
necessarily OK.   When the site transmits a program
to the user, it is
not enough for the program to be written in a documented and
unencumbered language; that program must be free, too.  “Only   free
programs transmitted to the user” must become part of the criterion
for proper behavior by  web sites.</p> 

<p>Silently loading and running nonfree programs is one among several
issues raised by "web applications".   The term "web
application"  was designed to disregard the fundamental
distinction between software delivered to users and software running
on a server.  It can refer to a specialized client program running
in a browser; it can refer to specialized server software; it can
refer to a specialized client program that works hand in hand with
specialized server software.  The client and server sides raise
different ethical issues, even if they are so closely integrated that
they arguably form parts of a single program.  This article addresses
only the issue of the client-side software.  We are addressing the
server issue separately.</p>

<p>In practical terms, how can we deal with the problem of  nonfree
JavaScript programs in web sites?  The first step is to avoid running
it.</p>

<p>What do we mean by "nontrivial"?   It is a matter of
degree, so this is a matter of designing a simple criterion that gives
good results, rather than finding the one correct answer.</p>
<p>
Our tentative policy  is to consider a JavaScript program nontrivial if:</p>


<ul>
  <li>it makes an AJAX request or is loaded along with scripts that make  an AJAX request,</li>

  <li>it loads external scripts dynamically  or is loaded along with
    scripts  that do,</li> 

  <li>it defines 
      functions or methods  and either loads an external script
    (from html) or is loaded as one,</li> 
  
  <li>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:
    <ul>
      <li>using the eval function,</li>
      <li>calling methods with the square bracket notation,</li>
      <li>using   any other
    construct than a string literal with certain methods (Obj.write, Obj.createElement, ...).</li>
    </ul>
  </li>
    
</ul>

<p>How do we tell whether the JavaScript code is free?  At the end of
this article  
we propose a convention  by which a nontrivial JavaScript
program in a web page can state the URL where its source code is
located, and can state its license too, using stylized comments.</p>

<p>Finally, we need to change free browsers to detect and block
nontrivial nonfree JavaScript in web pages.  The program
<a href="/software/librejs/">LibreJS</a> detects nonfree,
nontrivial JavaScript in pages you visit, and blocks it.  LibreJS is
 an add-on for IceCat and IceWeasel (and Firefox).</p> 

<p>Browser users also need a convenient facility to specify JavaScript
code to use <em>instead</em> of the JavaScript in a certain page.
(The specified code might be total replacement, or a modified version
of the free JavaScript program in that page.)  Greasemonkey comes close
to being able to do this, but not quite, since it doesn't guarantee to
modify the JavaScript code in a page before that program starts to
execute.  Using a local proxy works, but is too inconvenient now to be
a real solution.  We need to construct a solution that is reliable and
convenient, as well as sites for sharing changes.  The GNU Project
would like to recommend sites which are dedicated to free changes
only.</p>

<p>These features will make it possible for a JavaScript program included
in a web page to be free in a real and practical sense.  JavaScript
will no longer be a particular obstacle to our freedom—no more than
C and Java are now.  We will be able to reject and even replace the
nonfree nontrivial JavaScript programs, just as we reject and replace
nonfree packages that are offered for installation in the usual way.
Our campaign for web sites to free their JavaScript can then begin.</p>

<p>In the mean time, there's one case where it is acceptable to run a
nonfree JavaScript program: to send a complaint to the website
operators saying they should free or remove the JavaScript code in the
site.  Please don't hesitate to enable JavaScript temporarily to do
that—but remember to disable it again afterwards.</p>

<p><strong>Thank you to <a href="/people/people.html#mattlee">Matt Lee</a>
and <a href="http://ejohn.org">John Resig</a> for their help in
defining our proposed criterion, and to David Parunakian for
helping to make me aware of the problem.</strong></p>

<h3 id="AppendixA">Appendix A: a convention for releasing free JavaScript programs</h3>

<p>For references

 to corresponding source code, we recommend</p>
<pre dir="ltr">

    // @source:

</pre>

<p>followed by the URL.  This satisfies the GNU GPL's requirement  to
distribute source code.  If the source is on a different site, you
must take care  to
     
<a href="/licenses/gpl-faq.html#SourceAndBinaryOnDifferentSites">
handle that properly</a>.  Source code is necessary for the program 
to
be free.
</p>

<p>To indicate the license of the JavaScript code embedded in a page, we
recommend putting the license notice between two notes of this form:</p>
<pre dir="ltr">
<!--TRANSLATORS: Do not translate these license notices.  The <pre>
    elements have dir="ltr" explicitly set to cater for RTL languages.-->
    @licstart  The following is the entire license notice for the 
    JavaScript code in this page.
    ...
    @licend  The above is the entire license notice
    for the JavaScript code in this page.

</pre>
<p>Of course, all of this should be contained  in a multiline comment.</p>

<p>The  <a href="/licenses/gpl.html">GNU GPL</a>, like many other free
software licenses, requires distribution of a copy of the license with
both source 
and binary forms of the program.  However, the GNU GPL is
long enough that including it in a page with a JavaScript program can
be inconvenient.  You can remove that requirement,  for code that you
have the copyright on, with a license notice like this:</p>
<pre dir="ltr">

    Copyright (C) YYYY  Developer

    The JavaScript code  in this page is free software: you can
    redistribute it and/or modify it under the terms of the GNU
    General Public License (GNU GPL) as published by the Free Software
    Foundation, either version 3 of the License, or (at your option)
    any later version.  The code is distributed WITHOUT ANY WARRANTY;
    without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE.  See the GNU GPL for more details.

    As additional permission under GNU GPL version 3 section 7, you
    may distribute non-source (e.g., minimized or compacted) forms of
    that code without the copy of the GNU GPL normally required by
    section 4, provided you include this license notice
 and a URL
    through which recipients can access the Corresponding Source.

</pre>

<p>I thank Jaffar Rumith  for
bringing this issue  to my attention.</p>

<h3 id="AppendixB">Appendix B: Publishing free JavaScript programs as
  a webmaster</h3>

<p>If you're a webmaster deploying free JavaScript software
  on your site, clearly and consistently publishing information about
  those files' licenses and source code helps your visitors make
  sure that they're running free software, and help you comply with
  license conditions.</p>

<p>One method of stating the licenses is the one described above in
  <a href="#AppendixA">Appendix A</a>.  A second
  method, <a href="/licenses/javascript-labels.html"> JavaScript
  license web labels</a>, can be more convenient for libraries of
  minified JavaScript code, especially when you didn't write them.</p>


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