Javascript library: to obfuscate or not to obfuscate - that is the question [closed]

I need to write a GUI related javascript library. It will give my website a bit of an edge (in terms of functionality I can offer) - up until my competitors play with it long enough to figure out how to write it by themselves (or finally hack the downloaded script). I can accept the fact that it will be emulated over time - thats par for the course (its part of business). I just want to have a few months breathing space where people go "Wow - how the f*** did they do that?" - which gives me a few months of free publicity and some momentum to move onto other things.

To be clear, I am not even concerned about hard core hackers who will still hack the source - thats a losing battle not worth fighting (and in any case I accept that my code is not "so precious"). However, what I cannot bear, is the idea of effectively, simply handing over all the hard work that would have gone into the library to my competitors, by using plain javascript that anyone can download and use. If someone is going to use what I have worked on, then I sure as hell don't want to simply hand it over to them - I want them to work hard at decoding it. If they can decode it, they deserve to have the code (they'll most likely find out they could have written better code themselves - they just didn't have the business sense to put all the [plain vanilla] components in that particular order) - So, I'm not claiming that no one could have written this (which would be a preposterous claim in any case) - but rather, what I am saying is that no one (up to now) has made the functionality I am talking about, available to this particular industry - and I (thinking as an entrepreneur rather than a geek/coder), want to milk it for all its worth, while it lasts i.e until it (inevitably) gets hacked.

It is an established fact that not one website in the industry I am "attacking" has this functionality, so the value of such a library is undeniable and is not up for discussion (i.e. thats not what I'm asking here).

What I am seeking to find out are the pros and cons of obfuscating a javascript library, so that I can come to a final decision.

Two of my biggest concerns are debugging, and subtle errors that may be introduced by the obfuscator.

I would like to know:

  1. How can I manage those risks (being able to debug faulty code, ensuring/minimizing against obfuscation errors)

  2. Are there any good quality industry standard obfuscators you can recommend (preferably something you use yourself).

  3. What are your experiences of using obfuscated code in a production environment?



If they can decode it, they deserve to have the code (they'll most likely find out they could have written better code themselves - they just didn't have the business sense to put all the [plain vanilla] components in that particular order).

So really, you're trying to solve a business issue with technical measures.

Anybody worth his salt as a Javascript programmer should be able to recreate whatever you do pretty easily by just looking at the product itself, no code needed. It's not like you're inventing some new magical thing never seen before, you're just putting pieces together in a new way, as you admit yourself. It's just Javascript.

Even if you obfuscate the script, it'll still run as-is, competitors could just take it and run with it. A few customizations shouldn't be too hard even with obfuscated code.

In your niche business, you'll probably notice pretty quickly if somebody "stole" your script. If that happens, it's a legal issue. If your competitors want to be in the clear legally, they'll have to rewrite the script from scratch anyway, which will automatically buy you some time.

If your competitors are not technically able to copy your product without outright stealing the code, it won't make a difference whether the code is in the clear or obfuscated.


While you can go down the long, perilous road of obfuscators, you generally don't see them used on real, production applications for the simple reason that they don't really do much. You'll notice that Google apps, which is really a whole heap of proprietary and very valuable JavaScript when you get down to it, is only really minimized and not obfuscated, though the way minimizers work now, they are as good as obfuscated. You really need to know what you're doing to extract the meaning from them, but the determined ones will succeed.

The other problem is that obfuscated code must work, and if it works, people can just rip it wholesale, not understanding much of it, and use it as they see fit in that form. Sure, they can't modify it directly, but it isn't hard to layer on some patches that re-implement parts they don't like without having to get in too deep. That is simply the nature of JavaScript.

The reason Google and the like aren't suffering from a rash of cut-and-paste competitors is because the JavaScript is only part of the package. In order to have any degree of control over how and where these things are used, a large component needs to be server-based. The good news is you can leverage things like Node.js to make it fairly easy to split client and server code without having to re-implement parts in a completely different language.

What you might want to investigate is not so much obfuscating, but splitting up your application into parts that can be loaded on-demand from some kind of service, and as these parts can be highly inter-dependent and mostly non-functional without this core server, you can have a larger degree of control over when and where this library is used.

You can see elements of this in how Google is moving to a meta-library which simply serves as a loader for their other libraries. This is a step towards unifying the load calls for Google Apps, Google AdSense, Google Maps, Google Adwords and so forth.

If you wanted to be a little clever, you can be like Google Maps and add a poison pill your JavaScript libraries as they are served dynamically so that they only operate in a particular subdomain. This requires generating them on an as-needed basis, and while it can always be removed with sufficient expertise, it prevents wholesale copy-paste usage of your JavaScript files. To insert a clever call that validates document.href is not hard, and to find all these instances in an aggressively minimized file would be especially infuriating and probably not worth the effort.


Javascript obfuscation facts:

  • No one can offer a 100% crack free javascript obfuscation. This means that with time and knowledge every obfuscation can be "undone".
  • Minify != obfuscation: When you minify your objective is: reduce code size. Minified code looks completly different and its much more complex to read ( Obfucation has a completly different objective: to protect the code. The transformations used try to protect Obfuscated code from debugging and eavesdropping. Obfuscation can even produce a even bigger version of the original code which is completely contrary to the objectives of minification.
  • Obfuscation != encryption - This one is obvious but its common mistake people make.
  • Obfuscation should make debugging much much harder, its one of it objectives. So if it is done correctly you can expect to loose a lot of time trying to debug obfuscated code.That said, if it is done correctly the introduction of new errors is a rare issue and you can easily find if it is an obfuscation error by temporarily replacing the code with non obfuscated code.
  • Obfuscation is NOT a waste of time - Its a tool. If used correctly you can make others waste lots of time ;)

Javascript obfuscation fiction: ( I will skip this section ;) )

Answer to Q2 - Sugested obfuscation tools:

  • For an extensive list of javascript obfuscator: My personal choice is

Answer to Q3 - experiences of using obfuscated code

  • To date no new bugs introduced by obfuscation
  • Much better client retention. They must come to the source to get the source;)
  • Occasional false positives reported by some anti-virus tools. Can be tested before deploying any new code using a tool like

Standard answer to obfuscation questions: Is using an obfuscator enough to secure my JavaScript code?

IMO, it's a waste of time. If the competitors can understand your code in the clear (assuming it's anything over a few thousand lines...), they should have no trouble deobfuscating it.

How can I manage those risks (being able to debug faulty code, ensuring/minimizing against obfuscation errors)

Obfuscation will cause more bugs, you can manage them by spending the time to debug them. It's up to the person who wrote the obfuscation (be it you or someone else), ultimately it will just waste lots of time.

What are your experiences of using obfuscated code in a production environment?

  1. Being completely bypassed by side channel attacks, replay attacks, etc.
  2. Bugs.

Google's Closure Complier obfuscates your code after you finish writing it. That is, write your code, run it through the compiler, and publish the optimized (and obfuscated) js.

You do need to be careful if your using external js that interfaces with the lib though because it changes the names of your objects so you can't tell what is what.


Automatic full-code obfuscation is so far only available in the Closure Compiler's Advanced mode.

Code compiled with Closure Advanced mode is almost impossible to reverse-engineer, even passing through a beautifier, as the entire code base (includinhg the library) is obfuscated. It is also 25% small on average.

JavaScript code that is merely minified (YUI Compressor, Uglify etc.) is easy to reverse-engineer after passing through a beautifier.

If you use a JavaScript library, consider Dojo Toolkit which is compatible (after minor modifications) with the Closure Compiler's Advanced mode compilation.


You could adopt an open-source business model and license your scripts with the GPL or Creative Commons BY-NC-ND or similar


While obfuscation in general is a bad thing, IMHO, with Javascript, the story is a little different. The idea is not to obfuscate the Javascript itself but to produce shorter code length (bandwidth is expensive, and that first-time users may just be pissed off waiting for your Javascript to load the first time). Initially called minification (with programs such as minify), it has evolved quite a bit and now a full compiler is available, such as YUI compiler and Google Closure Compiler. Such compiler performs static checking (which is a good thing, but only if you follow the rules of the compiler), minification (replace that long variable name with 'ab' for example), and many other optimization techniques. At the end, what you got is the best of both worlds, coding in non-compiled code, and deploying compiled (, minified, and obfuscated) code. Unfortunately, you would of course need to test it more extensively as well.


The truth is obfuscator or not, any programmer worth his salt could reproduce whatever it is you did in about as much time as it took you. If they stole what you did you could sue them. So bottom line from the business point of view is that you have, from the moment you publish, roughly the same amount of time it took you to implement your design until a competitor catches up. Period. That's all the head start you get. The rest is you innovating faster than your competitors and marketing it at least as well as they do.


Write your web site in flash, or better yet in Silverlight. This will give your company unmatched GUI, that your competitors will be salivating about. But compiled nature of flash/dotnet will not allow them easily pick into your code. It's a win/win situation for you ;)


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