Why is JS interpreted and not compiled? [closed]

Why is JS interpreted and not compiled? [closed] - javascript

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I've read a lot of things about interpretation, compilation, just-in-time compilation, etc. But I haven't found a clear explanation about why JS was created as an interpreted language and why there is still no ability to compile js code.
I have some thoughts, but I'm not sure about any of them:
If the browser could execute (or just pass to OS) a binary code it would be a big vulnerability because any command could be injected into a binary code (e.g. delete all files from the file system). If it's true is it possible to teach the browser to validate somehow a binary code? And it's not a problem for a back-end side. Then, why NodeJS can't execute compiled JS (the same for PHP, Python, why they are interpreted)?
Optimization isn't possible for binary code. Is it really true? Is optimized interpreted js faster than compiled (to binary) js?
Different CPUs (architectures) need different binary codes. That means it's impossible to generate a universal binary code for any client. That's why WebAssembly modules use some intermediate code? And again why to not use compiled code for a back-end?
If anyone could explain some of the above or any other reasons I would be very grateful.

Let's first say that unless you were in the design discussions for Javascript in its early days, none of us actually "know" why. The best we can do is try to infer why certain choices might have been made given the objectives they had and the choices they had.
If you look at the requirements for the original design of Javascript in web pages, you see things like this:
Must run on lots of platforms.
Must be easily embeddable in HTML pages.
Must be simple to program.
Is not initially an environment that feels the need to maximize execution performance.
Not Java.
Let's look at these...
About #1, OK, run on lots of platforms means it cannot be compiled to native machine code - period. It could be compiled to a universal byte code like Java or webAssembly, but read on about the other requirements.
About #2, it wants to be embeddable in web pages so you can do things like:
<div onclick='alert("hi")'>Click me</div>
Then, it's pretty hard to have code that is compiled in advance fit in there. You'd probably have to compile your whole web page. That creates an entirely new paradigm and browser (that expects pre-compiled code and HTML). While the world could have eventually gone there, that certainly wasn't an easy way to go (requiring a redo of the browser).
About #3, "simple to program", it's generally believed that interpreted "scripts" are simpler for people to start with than languages that need a programming environment and compiler set up and some build tools. It's faster and simpler to do simple things.
About #4, "performance". In the early days of Javascript, it was an auxiliary language to help add some client-side logic to web pages. The initial target was far simpler than what Javascript is being used for today. I rather doubt it was envisioned that a pre-compiled language was needed for what its initial target was. So, keep it simple and go with the simpler way of reaching your target.
About #5: "not Java". Java was a known tool of the day. But, Java was not super simple, required pre-compiling, had IP encumbrances, etc... So, Javascript was born to be something that was familiar to both C and Java developers, but was far simpler for someone new to pick up. Easy to do simple things.
As for environments like nodejs, they could more practically have a pre-compile step, but the early designers of nodejs decided to use the open source V8 Javascript engine rather than make their own Javascript engine. Plus, in a server world, your code is generally loaded once at server startup where V8 compiles it to a combination of native code and byte code anyway so requiring developers to pre-compile it doesn't necessarily buy you a lot anyway. This is where it matters that Javascript is now actually compiled, it's just compiled upon loading rather than requiring pre-compiling by the developer.
And, nowadays, if you want the benefits of type checking in a pre-compile step, you can use TypeScript and precompile that to Javascript.

Related

Can you compile JS code using V8 and feed that directly to Chrome?

I'm looking for a way to protect some javascript code from reading/modifying. I know many people consider that impossible, but still...
From what I see the Chrome's V8 engine does a number of optimizations when it sees JS code, probably compiles it (?) and then runs it.
So I'm wondering is it possible to use V8's C++ api to compile the JS code into machinecode/chromecode and then feed that directly into Chrome (I don't care about other browsers)?
Supposedly it will not only be faster, but also non-humanly readable, something like ASM.
Is this possible?
WebAssembly is doing this thing so I don't understand why we can't do it with JS code.
There's also EncloseJS and pkg that are doing a very similar thing.

V8 developer here. No, it is not possible to compile JavaScript ahead of time and send only the compiled code to the browser. V8 (and other virtual machines like it) contain compilers, but they cannot be used as standalone compilers to produce standalone binaries.
In theory, you could compile JavaScript to WebAssembly -- any two turing-complete programming languages can in theory be compiled to each other. As far as I know, no such compiler exists today though. One big reason for that is that performance of the end result would be horrible (see the discussion with Andreas Rossberg for details); so considering that browsers can execute JavaScript directly, people have little reason to develop such a thing. (It would also be a large and difficult task.)
As for your stated goal: your best shot at making JavaScript code unreadable is to minify it. In fact, that is effectively just as good as your idea to generate assembly, because disassemblers exist that turn assembly back into minified-like higher-level language code; they cannot reconstruct variable names or comments (because that information is lost during compilation), but they can reconstruct program logic.

What I ended up doing is moving some of the logic from JavaScript into C++ and compiling that into NodeJS native modules (that's possible for Electron apps).
It works pretty good, it's very fast, the source is... as protected as it can get, but you may need to worry about cross-platform issues, also compiling/linking can be a bit of a pain, but other than that it's great.

WebAssembly is not doing that. And no, it's not possible either. The web is supposed to be both browser- and hardware-independent.
Moreover, a language like JS would not be faster if compiled offline -- it only is anything close to fast because it is dynamically compiled and optimised, taking dynamic profile information into account.

How can I defend my JavaScript game from robbers? [duplicate]

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I want to make a JavaScript application that's not open source, and thus I wish to learn how to can obfuscate my JS code? Is this possible?

Obfuscation:
Try YUI Compressor. It's a very popular tool, built, enhanced and maintained by the Yahoo UI team.
You may also use:
Google Closure Compiler
UglifyJS
UPDATE: This question was originally asked on 2008, and The mentioned technologies are deprecated. you can use:
terser - more information in web.dev.
Private String Data:
Keeping string values private is a different concern, and obfuscation won't really be of much benefit. Of course, by packaging up your source into a garbled, minified mess, you have a light version of security through obscurity. Most of the time, it's your user who is viewing the source, and the string values on the client are intended for their use, so that sort of private string value isn't often necessary.
If you really had a value that you never wanted a user to see, you would have a couple of options. First, you could do some kind of encryption, which is decrypted at page load. That would probably be one of the most secure options, but also a lot of work which may be unnecessary. You could probably base64 encode some string values, and that would be easier.. but someone who really wanted those string values could easily decode them. Encryption is the only way to truly prevent anyone from accessing your data, and most people find that to be more security than they need.
Sidenote:
Obfuscation in Javascript has been known to cause some bugs. The obfuscators are getting a little better about it, but many outfits decide that they see enough benefit from minifying and gzipping, and the added savings of obfuscation isn't always worth the trouble. If you're trying to protect your source, maybe you'll decide that it's worth your while, just to make your code harder to read. JSMin is a good alternative.

I'm surprised no one has mentioned Google's Closure Compiler. It doesn't just minify/compress, it analyzes to find and remove unused code, and rewrites for maximum minification. It can also do type checking and will warn about syntax errors.
JQuery recently switched from YUI Compresser to Closure Compiler, and saw a "solid improvement"

Obfuscation can never really work. For anyone who really wants to get at your code, it's just a speed bump. Worse, it keeps your users from fixing bugs (and shipping the fixes back to you), and makes it harder for you to diagnose problems in the field. Its a waste of your time and money.
Talk to a lawyer about intellectual property law and what your legal options are. "Open Source" does not mean "people can read the source". Instead, Open Source is a particular licensing model granting permission to freely use and modify your code. If you don't grant such a license then people copying your code are in violation and (in most of the world) you have legal options to stop them.
The only way you can really protect your code is to not ship it. Move the important code server-side and have your public Javascript code do Ajax calls to it.
See my full answer about obfuscators here.

You can obfuscate the javascript source all you want, but it will always be reverse-engineerable just by virtue of requiring all the source code to actually run on the client machine... the best option I can think of is having all your processing done with server-side code, and all the client code javascript does is send requests for processing to the server itself. Otherwise, anyone will always be able to keep track of all operations that the code is doing.
Someone mentioned base64 to keep strings safe. This is a terrible idea. Base64 is immediately recognizable by the types of people who would want to reverse engineer your code. The first thing they'll do is unencode it and see what it is.

There are a number of JavaScript obfuscation tools that are freely available; however, I think it's important to note that it is difficult to obfuscate JavaScript to the point where it cannot be reverse-engineered.
To that end, there are several options that I've used to some degree overtime:
YUI Compressor. Yahoo!'s JavaScript compressor does a good job of condensing the code that will improve its load time. There is a small level of obfuscation that works relatively well. Essentially, Compressor will change function names, remove white space, and modify local variables. This is what I use most often. This is an open-source Java-based tool.
JSMin is a tool written by Douglas Crockford that seeks to minify your JavaScript source. In Crockford's own words, "JSMin does not obfuscate, but it does uglify." It's primary goal is to minify the size of your source for faster loading in browsers.
Free JavaScript Obfuscator. This is a web-based tool that attempts to obfuscate your code by actually encoding it. I think that the trade-offs of its form of encoding (or obfuscation) could come at the cost of filesize; however, that's a matter of personal preference.

What i would do:
A. Troll the hacker!
This is will be in the second part my fake/obfuscated secret javascript code LAUNCHER.
The one you see in the source code.
What does this code?
loads the real code
sets a custom header
posts a custom variable
var ajax=function(a,b,d,c,e,f){
e=new FormData();
for(f in d){e.append(f,d[f]);};
c=new XMLHttpRequest();
c.open('POST',a);
c.setRequestHeader("Troll1","lol");
c.onload=b;
c.send(e);
};
window.onload=function(){
ajax('Troll.php',function(){
(new Function(atob(this.response)))()
},{'Troll2':'lol'});
}
B. Obfuscate the code a little
What is that?
thats the same code as above in base64
this is not the SECRET javascript code
(new Function(atob('dmFyIGFqYXg9ZnVuY3Rpb24oYSxiLGQsYyxlLGYpe2U9bmV3IEZvcm1EYXRhKCk7Zm9yKGYgaW4gZCl7ZS5hcHBlbmQoZixkW2ZdKTt9O2M9bmV3IFhNTEh0dHBSZXF1ZXN0KCk7Yy5vcGVuKCdQT1NUJyxhKTtjLnNldFJlcXVlc3RIZWFkZXIoIlRyb2xsMSIsImxvbCIpO2Mub25sb2FkPWI7Yy5zZW5kKGUpO307d2luZG93Lm9ubG9hZD1mdW5jdGlvbigpe2FqYXgoJ1Ryb2xsLnBocCcsZnVuY3Rpb24oKXsgKG5ldyBGdW5jdGlvbihhdG9iKHRoaXMucmVzcG9uc2UpKSkoKX0seydUcm9sbDInOidsb2wnfSk7fQ==')))()
C Create a hard to display php file with the real code inside
What does this php code?
Checks for the right referrer (domain/dir/code of your launcher)
Checks for the custom HEADER
Checks for the custom POST variable
If everything is ok it will show you the right code else a fake code or ban ip, close page.. whatever.
<?php
$t1=apache_request_headers();
if(base64_encode($_SERVER['HTTP_REFERER'])=='aHR0cDovL2hlcmUuaXMvbXkvbGF1bmNoZXIuaHRtbA=='&&$_POST['Troll2']=='lol'&&$t1['Troll1']='lol'){
echo 'ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg==';//here is the SECRET javascript code
}else{
echo 'd2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs=';
};
?>
base64 referrer = http://here.is/my/launcher.html
SECRET javascript = document.body.appendChild(document.createElement('div')).innerText='Awesome';
FAKE = window.open('', '_self', '');window.close();
Now .. if you define event handlers in the SECRET javascript it's probably accessible.. you need to define them outside with the launchcode and pointing to a nested SECRET function.
SO... is there a easy wayto get the code?
document.body.appendChild(document.createElement('div')).innerText='Awesome';
I'm not sure if this works but i'm using chrome and checked Elements,Resources,Network,Sources,Timeline,Profiles,Audits but i didn't find the line above.
note1: if u open the Troll.php url from Inspect element->network in chrome you get the fake code.
note2: the whole code is written for modern browsers. polyfill needs alot more code.
EDIT
launcher.html
<!doctype html><html><head><meta charset="utf-8"><title></title><script src="data:application/javascript;base64,KG5ldyBGdW5jdGlvbihhdG9iKCdkbUZ5SUdGcVlYZzlablZ1WTNScGIyNG9ZU3hpTEdRc1l5eGxMR1lwZTJVOWJtVjNJRVp2Y20xRVlYUmhLQ2s3Wm05eUtHWWdhVzRnWkNsN1pTNWhjSEJsYm1Rb1ppeGtXMlpkS1R0OU8yTTlibVYzSUZoTlRFaDBkSEJTWlhGMVpYTjBLQ2s3WXk1dmNHVnVLQ2RRVDFOVUp5eGhLVHRqTG5ObGRGSmxjWFZsYzNSSVpXRmtaWElvSWxSeWIyeHNNU0lzSW14dmJDSXBPMk11YjI1c2IyRmtQV0k3WXk1elpXNWtLR1VwTzMwN2QybHVaRzkzTG05dWJHOWhaRDFtZFc1amRHbHZiaWdwZTJGcVlYZ29KMVJ5YjJ4c0xuQm9jQ2NzWm5WdVkzUnBiMjRvS1hzZ0tHNWxkeUJHZFc1amRHbHZiaWhoZEc5aUtIUm9hWE11Y21WemNHOXVjMlVwS1Nrb0tYMHNleWRVY205c2JESW5PaWRzYjJ3bmZTazdmUT09JykpKSgp"></script></head><body></body></html>
Troll.php
<?php $t1=apache_request_headers();if(/*base64_encode($_SERVER['HTTP_REFERER'])=='PUT THE LAUNCHER REFERER HERE'&&*/$_POST['Troll2']=='lol'&&$t1['Troll1']='lol'){echo 'ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg==';}else{echo 'd2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs=';}; ?>

The problem with interpreted languages, is that you send the source to get them working (unless you have a compiler to bytecode, but then again, it is quite trivial to decompile).
So, if you don't want to sacrifice performance, you can only act on variable and function names, eg. replacing them with a, b... aa, ab... or a101, a102, etc. And, of course, remove as much space/newlines as you can (that's what so called JS compressors do).
Obfuscating strings will have a performance hit, if you have to encrypt them and decrypt them in real time. Plus a JS debugger can show the final values...

Try JScrambler. I gave it a spin recently and was impressed by it.
It provides a set of templates for obfuscation with predefined settings for those who don't care much about the details and just want to get it done quickly. You can also create custom obfuscation by choosing whatever transformations/techniques you want.

Contrary to most of the other answers I suggest against YUI Compressor; you should use Google Closure.
Not much because it compresses more, but mostly because it will catch javascript errors such as a = [1,2,3,]; which make IE go haywire.

I can recommend JavaScript Utility by Patrick J. O'Neil. It can obfuscate/compact and compress and it seems to be pretty good at these. That said, I never tried integrating it in a build script of any kind.
As for obfuscating vs. minifying - I am not a big fan of the former. It makes debugging impossible (Error at line 1... "wait, there is only one line") and they always take time to unpack. But if you need to... well.

A non-open-source Javascript-based application is fairly silly. Javascript is a client-side interpreted language.. Obfuscation isn't much protection..
JS obfuscation is usually done to reduce the size of the script, rather than "protect" it. If you are in a situation where you don't want your code to be public, Javascript isn't the right language..
There are plenty of tools around, but most have the word "compressor" (or "minifier") in its name for a reason..

You can't secure client side code: just press F12 on Google Chrome, pause javascript execution and you will get all strings, even those encrypted. Beautify it and rename variables and you will get almost the original code.
If you're writing server side javascript (i.e. NodeJS) is afraid of someone hacking into your server and want to make the hacker work more difficult, giving you more time to get your access back, then use javacript compilers:
You need to use Closure Compiler on Advanced Compilation, as it's the only tool that renames all your variables, even if those are used in multiple files/modules. But it just have a problem: it only work if you write in it's coding style.

I would suggest first minify with something like YUI Compressor, and then convert all string and numbers to HEX Values using something like http://www.javascriptobfuscator.com/
With this, the code would be rendered near impossible to understand and I think at this Stage it will take more time for a Hacker to re-enact your code than actually if he re-wrote from scratch. Rewriting and Cloning is what you cant actually stop. After all we are free-people !

Try this tool Javascript Obfuscator
I used it on my HTML5 game not only it reduced it size from 950KB to 150 but also made the source code unreadable closure compilers and minifiers are reversable I personally dont know how to reverse this obfuscation.

Dean Edward's Packer is an excellent obfuscator, though it primarily obfuscates the code, not any string elements you may have within your code.
See: Online Javascript Compression Tool and select Packer (Dean Edwards) from the dropdown

I'm under the impression that some enterprises (e.g.: JackBe) put encrypted JavaScript code inside *.gif files, rather than JS files, as an additional measure of obfuscation.

I've been using Jasob for years and it is hands down the best obfuscator out there.
It has an advanced UI but is still intuitive and easy to use.
It will also handle HTML and CSS files.
The best way to use it is to prefix all of your private variables with something like an underscore, then use the sort feature to group them all together and check them off as targets for obfuscation.
Users can still view your source, but it's much more difficult to decipher when your private variables are converted from something like _sUserPreferredNickName to a.
The engine will automatically tally up the number of targeted variables and prioritize them to get the maximum compression.
I don't work for Jasob and I get nothing out of promoting them, just offering some friendly advice.
The downside is that it's not free and is a little pricey, but still worth it when stacked against alternatives - the 'free' options don't even come close.

Have you tried Bananascript? It produces highly compressed and completely unreadable code.

I am using Closure-Compiler utility for the java-script obfuscation. It minifies the code and has more options for obfuscation.
This utility is available at Google code at below URL:
Closure Tools
But now a days I am hearing much of UglifyJS. You can find various comparison between Closure Compiler and UglifyJS in which Uglify seems to be a winner.
UglifyJS: A Fast New JavaScript Compressor For Node.js That’s On Par With Closure
Soon I would give chance to UglifyJS.

As a JavaScript/HTML/CSS obfuscator/compressor you can also try Patu Digua.

You definitely should consider taking a look at Obfuscriptor.
I goes beyond the typical Javascript minifying tricks we've seen from other tools such as YUI Compressor or Google Closure.
The obfuscated code looks more like encrypted. Unlike anything I've seen before.

I've used this in the past, and it does a good job. It's not free, but you should definitely take a look.
JavaScript Obfuscator & Encoder

Javascript and Scientific Processing? [closed]

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Matlab, R, and Python are powerful but either costly or slow for some data mining work I'd like to do. I'm considering using Javascript both for
speed, good visualization libraries, and to be able to use the browser as an interface.
The first question I faced is the obvious one for science programming, how to do I/O to data files? The second is client-side or server-side? The last question, can I make something that is truly portable i.e. put it all on a USB and run from that?
I've spent a couple of weeks looking for answers. Server2go seems to address client/server needs which I think means I can get data to and from the programs on the client side. Server2go also allows running from a USB. The data files I work with are usually XML and there seem to be several javascript converters to JSON.
However, after all the looking around, I'm not sure if my approach makes sense. So before I commit further, any advice/thoughts/guidance on Javascript as a portable tool for scientific data processing?

I have to agree with the comments that JavaScript is not a good fit for scientific processing. However, you know your requirements best; maybe you already found useful libraries that do what you need. Just be aware that you'll have to implement all logic yourself. There is no built in handling of complex numbers, or matrices or integrals or ... Usually programmer time is far more valuable than machine time. Personally, I'd look in to compiled languages; after I created a first version that isn't fast enough in whatever language I like the most.
Assuming that JavaScript is the way to go:
Data I/O
I can think of three options:
Sending and receiving data with ajax to a server
Seems to be the solution you've found with Server2go. It requires you to write a server back end, but that can be kept quite simple. All it really needs to do be able to read and write files as a response to you client-side application.
Using a non-browser implementation of v8 which includes file I/O
For instance Node.js. You could then avoid the need for a server and simply use a command-line interface, and all code will be JavaScript. Other than that it is roughly equivalent to the first option.
Creating a file object using the file API which you ask the user to save or load
It is the worst option in my opinion, as user interaction is required. It would avoid the need for a server; your application could be a simple html file that loads all data files with ajax requests. You'd have to start Chrome with a special switch to allow ajax requests with the file:// protocol, as described here
These options are only concerned with file I/O and you can't do file I/O in JavaScript. This is because browsers cannot allow arbitrary web code to do arbitrary file I/O; the security implications would be horrendous. Each option describes one way to not do file I/O.
The first communicates with a server that does the file I/O for the client.
The second uses "special" versions of JavaScript, with conditions other than that of the browser so the security implications are not important. But that means you'll have to look up how file I/O is done in the actual implementation you use, it's not common to JavaScript.
The third requires the user to control the file I/O.
Interface
Even if you don't use JavaScript to do the actual processing, which so far is the consensus, there is nothing stopping you from using a browser as the interface or JavaScript libraries for visualisation. That is something JavaScript is good at.
If you want to interactively control your data mining tool, you will need a server that can control the tool. Server2go should work, or the built in server in Node.js if you use that or... If you don't need interactive control of the data tool; that is you first generate the processed data, then look at the data a server can be avoided, by using the file//: protocol and JSONP. But really; avoiding a server shouldn't be a goal.
I won't go into detail about interface issues, as there is nothing specific to say and very nearly everything that has been written about javascript is about interface.
One thing, do use a declarative data binding library like Angular.js or Knockout.js.

JavaScript speed is heavily overrated. This is a Web 2.0 myth.
Let me explain this claim a bit (and don't just downvote me for saying something you do not want to hear!)
Sure, JavaScript V8 is a quite highly optimized VM. It does beat many other scripting languages in naive benchmarks.
However, it is a very limited scope language. It is meant for the "ADHS world" of web. It is a best effort, but it may just fail and you have little guarantees on things completing or completing on time.
Consider for example MongoDB. At first it seems to be good and fast and offer a lot. Until you see for example that the MapReduce is single-threaded only and thus really slow. It's not all gold that shines!
Now look at data mining relevant libraries such as BLAS. Basic linear algebra, math operations and such. All CPU manufacturers like Intel and AMD offer optimized versions for their CPUs. This is an optimization that requires detailed understanding of the individual CPUs, way beyond the capabilities of our current compilers. The libraries contain optimized codepaths for various CPUs all essentially doing the same thing.
And for these operations, using an optimized library such as BLAS can easily yield a 5-20x speedup; at the same time matrix operations that are often in O(n^2) or O(n^3) will dominate your overall runtime.
So a good language for data mining will let you go all the way to machine code!
Pythons SciPy and R are good choices here. They have the optimized libraries inside and easily accessible, but at the same time allow to do the wrapper stuff in a simpler language.
Have a look at this programming language benchmark:
http://benchmarksgame.alioth.debian.org/u32/which-programs-are-fastest.html
Pure JavaScript has a high variance, indicating that it can do some things fast (mostly regular expressions!) others much slower. It can clearly beat PHP, but it will be just as clearly be beaten by C and Java.
Multithreading is also important for modern data mining. Few large systems today have a single core, and you do want to make use of all cores. So you need libraries and a programming language that has a powerful set of multithreading operations. This is actually why Fortran and C are losing popularity here. Other languages such as Java are much better here.

Although this discussion is a bit old and I am not a Javascript guru by any stretch of the imagination, I find the above arguments doubtful about not having the processing speed or the capabilities for advance math operations. WebGL is a Javascipt API for rendering advance 2D and 3D graphics which relies heavily on advance math operations. I believe the capabilities are there from a technical point of view however what is lacking is good libraries to handling statistical analysis, natural language processing and other predictive analytics included in data mining.
WebGL is based on openGL, which in turn uses libraries like BLAS (library info here).
Advances like node.js, w8 make it technically possible. What is lacking is libraries like we can find in R and Scilab to do the same operations.

Interpreting and/or receiving dotNet code at run-time

Html can contain little bits of Javascript embedded in it (e.g. defined in onclick event handlers).
If I were writing an Html browser using a dotNet language like C#, what technologies or APIs could I use to run such Javascript fragments, given that I don't receive it until run-time (and receive it as string data, not as executable code)?
Is it any easier or harder if the code to be run were C# snippets rather than Javascript?
Is there any technique which doesn't require my code to have unusual priviledges? For example, a method like CodeCompiler.FromSource requires SecurityPermissionFlag.UnmanagedCode (which seems to me excessive: I don't see why it's so risky to compile code).
If I controlled the server-side as well as the client-side code, I could also consider compiling such script fragments on the server instead of on the client, and then sending it as precompiled code to the client side to be executed. Is there a way to send such code (a dotNet assembly, presumably) over the network to the client, have client-side code receive it from the network into client-side RAM, and invoke it on the client side without storing it as a file on a client-side disk drive?
Edit
I have answer to the first three questions: I've resigned myself to the fact that compiling takes high privileges. I don't see why; maybe (although I don't find this a very convincing reason) it's because the compiler is implemented using unmanaged code. Maybe this will change when they reimplement the compiler using managed code, in maybe the "C# version 5" timeframe. In any case, whatever the reason, that seems to be the way it is, and there are no work-arounds (other similar APIs but which require fewer privileges).
My remaining question then is how to get an Assembly instance from one machine to another. When I have time I'll find out whether untrusted code can run the Assembly.Load(byte[] rawAssembly) method.

Server side Javascript is one of the languages supported by the .NET platform. I used it many times in the scenrios when you need to insert small code snippets into existing code. Runtime it can be loaded from i.e. database and compiled, so there is no preformance penalty.
From the standpoint of making the plumbing work (retrieveing the source, compiling it, etc.) there is no difference. With strongly typed languages though it is much more difficult to assemble code snippets into a compilable compilation unit.
Permissions is certanly a challenge. I am not sure about the specific permission you mentioned, but security is a concern, after all the source you compile can be anything and if you are not careful about the source of your code it can become the backdoor into your system
The answer to this one is - yes of course. You can load an assembly from anywhere, not necessarily from a file, you can also compile in memory - that's what I do. There is no dll file in this case.

You're asking several questions, sort of, so I'll give you an idea on one of them.
There's a very good article and some code samples from:
http://www.west-wind.com/presentations/dynamicCode/DynamicCode.htm
which talks about compiling and executing C# code at runtime. I found it very useful and I am using this in a standard c# application. Seems like it would be usable for your problem as well.

How can I obfuscate (protect) JavaScript? [closed]

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I want to make a JavaScript application that's not open source, and thus I wish to learn how to can obfuscate my JS code? Is this possible?

Obfuscation:
Try YUI Compressor. It's a very popular tool, built, enhanced and maintained by the Yahoo UI team.
You may also use:
Google Closure Compiler
UglifyJS
UPDATE: This question was originally asked on 2008, and The mentioned technologies are deprecated. you can use:
terser - more information in web.dev.
Private String Data:
Keeping string values private is a different concern, and obfuscation won't really be of much benefit. Of course, by packaging up your source into a garbled, minified mess, you have a light version of security through obscurity. Most of the time, it's your user who is viewing the source, and the string values on the client are intended for their use, so that sort of private string value isn't often necessary.
If you really had a value that you never wanted a user to see, you would have a couple of options. First, you could do some kind of encryption, which is decrypted at page load. That would probably be one of the most secure options, but also a lot of work which may be unnecessary. You could probably base64 encode some string values, and that would be easier.. but someone who really wanted those string values could easily decode them. Encryption is the only way to truly prevent anyone from accessing your data, and most people find that to be more security than they need.
Sidenote:
Obfuscation in Javascript has been known to cause some bugs. The obfuscators are getting a little better about it, but many outfits decide that they see enough benefit from minifying and gzipping, and the added savings of obfuscation isn't always worth the trouble. If you're trying to protect your source, maybe you'll decide that it's worth your while, just to make your code harder to read. JSMin is a good alternative.

I'm surprised no one has mentioned Google's Closure Compiler. It doesn't just minify/compress, it analyzes to find and remove unused code, and rewrites for maximum minification. It can also do type checking and will warn about syntax errors.
JQuery recently switched from YUI Compresser to Closure Compiler, and saw a "solid improvement"

Obfuscation can never really work. For anyone who really wants to get at your code, it's just a speed bump. Worse, it keeps your users from fixing bugs (and shipping the fixes back to you), and makes it harder for you to diagnose problems in the field. Its a waste of your time and money.
Talk to a lawyer about intellectual property law and what your legal options are. "Open Source" does not mean "people can read the source". Instead, Open Source is a particular licensing model granting permission to freely use and modify your code. If you don't grant such a license then people copying your code are in violation and (in most of the world) you have legal options to stop them.
The only way you can really protect your code is to not ship it. Move the important code server-side and have your public Javascript code do Ajax calls to it.
See my full answer about obfuscators here.

You can obfuscate the javascript source all you want, but it will always be reverse-engineerable just by virtue of requiring all the source code to actually run on the client machine... the best option I can think of is having all your processing done with server-side code, and all the client code javascript does is send requests for processing to the server itself. Otherwise, anyone will always be able to keep track of all operations that the code is doing.
Someone mentioned base64 to keep strings safe. This is a terrible idea. Base64 is immediately recognizable by the types of people who would want to reverse engineer your code. The first thing they'll do is unencode it and see what it is.

There are a number of JavaScript obfuscation tools that are freely available; however, I think it's important to note that it is difficult to obfuscate JavaScript to the point where it cannot be reverse-engineered.
To that end, there are several options that I've used to some degree overtime:
YUI Compressor. Yahoo!'s JavaScript compressor does a good job of condensing the code that will improve its load time. There is a small level of obfuscation that works relatively well. Essentially, Compressor will change function names, remove white space, and modify local variables. This is what I use most often. This is an open-source Java-based tool.
JSMin is a tool written by Douglas Crockford that seeks to minify your JavaScript source. In Crockford's own words, "JSMin does not obfuscate, but it does uglify." It's primary goal is to minify the size of your source for faster loading in browsers.
Free JavaScript Obfuscator. This is a web-based tool that attempts to obfuscate your code by actually encoding it. I think that the trade-offs of its form of encoding (or obfuscation) could come at the cost of filesize; however, that's a matter of personal preference.

What i would do:
A. Troll the hacker!
This is will be in the second part my fake/obfuscated secret javascript code LAUNCHER.
The one you see in the source code.
What does this code?
loads the real code
sets a custom header
posts a custom variable
var ajax=function(a,b,d,c,e,f){
e=new FormData();
for(f in d){e.append(f,d[f]);};
c=new XMLHttpRequest();
c.open('POST',a);
c.setRequestHeader("Troll1","lol");
c.onload=b;
c.send(e);
};
window.onload=function(){
ajax('Troll.php',function(){
(new Function(atob(this.response)))()
},{'Troll2':'lol'});
}
B. Obfuscate the code a little
What is that?
thats the same code as above in base64
this is not the SECRET javascript code
(new Function(atob('dmFyIGFqYXg9ZnVuY3Rpb24oYSxiLGQsYyxlLGYpe2U9bmV3IEZvcm1EYXRhKCk7Zm9yKGYgaW4gZCl7ZS5hcHBlbmQoZixkW2ZdKTt9O2M9bmV3IFhNTEh0dHBSZXF1ZXN0KCk7Yy5vcGVuKCdQT1NUJyxhKTtjLnNldFJlcXVlc3RIZWFkZXIoIlRyb2xsMSIsImxvbCIpO2Mub25sb2FkPWI7Yy5zZW5kKGUpO307d2luZG93Lm9ubG9hZD1mdW5jdGlvbigpe2FqYXgoJ1Ryb2xsLnBocCcsZnVuY3Rpb24oKXsgKG5ldyBGdW5jdGlvbihhdG9iKHRoaXMucmVzcG9uc2UpKSkoKX0seydUcm9sbDInOidsb2wnfSk7fQ==')))()
C Create a hard to display php file with the real code inside
What does this php code?
Checks for the right referrer (domain/dir/code of your launcher)
Checks for the custom HEADER
Checks for the custom POST variable
If everything is ok it will show you the right code else a fake code or ban ip, close page.. whatever.
<?php
$t1=apache_request_headers();
if(base64_encode($_SERVER['HTTP_REFERER'])=='aHR0cDovL2hlcmUuaXMvbXkvbGF1bmNoZXIuaHRtbA=='&&$_POST['Troll2']=='lol'&&$t1['Troll1']='lol'){
echo 'ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg==';//here is the SECRET javascript code
}else{
echo 'd2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs=';
};
?>
base64 referrer = http://here.is/my/launcher.html
SECRET javascript = document.body.appendChild(document.createElement('div')).innerText='Awesome';
FAKE = window.open('', '_self', '');window.close();
Now .. if you define event handlers in the SECRET javascript it's probably accessible.. you need to define them outside with the launchcode and pointing to a nested SECRET function.
SO... is there a easy wayto get the code?
document.body.appendChild(document.createElement('div')).innerText='Awesome';
I'm not sure if this works but i'm using chrome and checked Elements,Resources,Network,Sources,Timeline,Profiles,Audits but i didn't find the line above.
note1: if u open the Troll.php url from Inspect element->network in chrome you get the fake code.
note2: the whole code is written for modern browsers. polyfill needs alot more code.
EDIT
launcher.html
<!doctype html><html><head><meta charset="utf-8"><title></title><script src="data:application/javascript;base64,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"></script></head><body></body></html>
Troll.php
<?php $t1=apache_request_headers();if(/*base64_encode($_SERVER['HTTP_REFERER'])=='PUT THE LAUNCHER REFERER HERE'&&*/$_POST['Troll2']=='lol'&&$t1['Troll1']='lol'){echo 'ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg==';}else{echo 'd2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs=';}; ?>

The problem with interpreted languages, is that you send the source to get them working (unless you have a compiler to bytecode, but then again, it is quite trivial to decompile).
So, if you don't want to sacrifice performance, you can only act on variable and function names, eg. replacing them with a, b... aa, ab... or a101, a102, etc. And, of course, remove as much space/newlines as you can (that's what so called JS compressors do).
Obfuscating strings will have a performance hit, if you have to encrypt them and decrypt them in real time. Plus a JS debugger can show the final values...

Try JScrambler. I gave it a spin recently and was impressed by it.
It provides a set of templates for obfuscation with predefined settings for those who don't care much about the details and just want to get it done quickly. You can also create custom obfuscation by choosing whatever transformations/techniques you want.

Contrary to most of the other answers I suggest against YUI Compressor; you should use Google Closure.
Not much because it compresses more, but mostly because it will catch javascript errors such as a = [1,2,3,]; which make IE go haywire.

I can recommend JavaScript Utility by Patrick J. O'Neil. It can obfuscate/compact and compress and it seems to be pretty good at these. That said, I never tried integrating it in a build script of any kind.
As for obfuscating vs. minifying - I am not a big fan of the former. It makes debugging impossible (Error at line 1... "wait, there is only one line") and they always take time to unpack. But if you need to... well.

A non-open-source Javascript-based application is fairly silly. Javascript is a client-side interpreted language.. Obfuscation isn't much protection..
JS obfuscation is usually done to reduce the size of the script, rather than "protect" it. If you are in a situation where you don't want your code to be public, Javascript isn't the right language..
There are plenty of tools around, but most have the word "compressor" (or "minifier") in its name for a reason..

You can't secure client side code: just press F12 on Google Chrome, pause javascript execution and you will get all strings, even those encrypted. Beautify it and rename variables and you will get almost the original code.
If you're writing server side javascript (i.e. NodeJS) is afraid of someone hacking into your server and want to make the hacker work more difficult, giving you more time to get your access back, then use javacript compilers:
You need to use Closure Compiler on Advanced Compilation, as it's the only tool that renames all your variables, even if those are used in multiple files/modules. But it just have a problem: it only work if you write in it's coding style.

I would suggest first minify with something like YUI Compressor, and then convert all string and numbers to HEX Values using something like http://www.javascriptobfuscator.com/
With this, the code would be rendered near impossible to understand and I think at this Stage it will take more time for a Hacker to re-enact your code than actually if he re-wrote from scratch. Rewriting and Cloning is what you cant actually stop. After all we are free-people !

Try this tool Javascript Obfuscator
I used it on my HTML5 game not only it reduced it size from 950KB to 150 but also made the source code unreadable closure compilers and minifiers are reversable I personally dont know how to reverse this obfuscation.

Dean Edward's Packer is an excellent obfuscator, though it primarily obfuscates the code, not any string elements you may have within your code.
See: Online Javascript Compression Tool and select Packer (Dean Edwards) from the dropdown

I'm under the impression that some enterprises (e.g.: JackBe) put encrypted JavaScript code inside *.gif files, rather than JS files, as an additional measure of obfuscation.

I've been using Jasob for years and it is hands down the best obfuscator out there.
It has an advanced UI but is still intuitive and easy to use.
It will also handle HTML and CSS files.
The best way to use it is to prefix all of your private variables with something like an underscore, then use the sort feature to group them all together and check them off as targets for obfuscation.
Users can still view your source, but it's much more difficult to decipher when your private variables are converted from something like _sUserPreferredNickName to a.
The engine will automatically tally up the number of targeted variables and prioritize them to get the maximum compression.
I don't work for Jasob and I get nothing out of promoting them, just offering some friendly advice.
The downside is that it's not free and is a little pricey, but still worth it when stacked against alternatives - the 'free' options don't even come close.

Have you tried Bananascript? It produces highly compressed and completely unreadable code.

I am using Closure-Compiler utility for the java-script obfuscation. It minifies the code and has more options for obfuscation.
This utility is available at Google code at below URL:
Closure Tools
But now a days I am hearing much of UglifyJS. You can find various comparison between Closure Compiler and UglifyJS in which Uglify seems to be a winner.
UglifyJS: A Fast New JavaScript Compressor For Node.js That’s On Par With Closure
Soon I would give chance to UglifyJS.

As a JavaScript/HTML/CSS obfuscator/compressor you can also try Patu Digua.

You definitely should consider taking a look at Obfuscriptor.
I goes beyond the typical Javascript minifying tricks we've seen from other tools such as YUI Compressor or Google Closure.
The obfuscated code looks more like encrypted. Unlike anything I've seen before.

I've used this in the past, and it does a good job. It's not free, but you should definitely take a look.
JavaScript Obfuscator & Encoder

Develop Reference

JavaScript is the programming language of the Web.