How do I protect javascript files?

I know it's impossible to hide source code but, for example, if I have to link a JavaScript file from my CDN to a web page and I don't want the people to know the location and/or content of this script, is this possible?

For example, to link a script from a website, we use:

<script type="text/javascript" src="http://somedomain.com/scriptxyz.js">
</script>

Now, is possible to hide from the user where the script comes from, or hide the script content and still use it on a web page?

For example, by saving it in my private CDN that needs password to access files, would that work? If not, what would work to get what I want?

Good question with a simple answer: you can't!

Javascript is a client-side programming language, therefore it works on the client's machine, so you can't actually hide anything from the client.
Obfuscating your code is a good solution, but it's not enough, because, although it is hard, someone could decipher your code and "steal" your script.
There are a few ways of making your code hard to be stolen, but as i said nothing is bullet-proof.

Off the top of my head, one idea is to restrict access to your external js files from outside the page you embed your code in. In that case, if you have

<script type="text/javascript" src="myJs.js"></script>

and someone tries to access the myJs.js file in browser, he shouldn't be granted any access to the script source.
For example, if your page is written in php, you can include the script via the include function and let the script decide if it's safe" to return it's source.
In this example, you'll need the external "js" (written in php) file myJs.php :

<?php
    $URL = $_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI'];
    if ($URL != "my-domain.com/my-page.php")
    die("/\*sry, no acces rights\*/");
?>
// your obfuscated script goes here

that would be included in your main page my-page.php :

<script type="text/javascript">
    <?php include "myJs.php"; ?>;
</script> 

This way, only the browser could see the js file contents.

Another interesting idea is that at the end of your script, you delete the contents of your dom script element, so that after the browser evaluates your code, the code disappears :

<script id="erasable" type="text/javascript">
    //your code goes here
    document.getElementById('erasable').innerHTML = "";
</script>

These are all just simple hacks that cannot, and I can't stress this enough : cannot, fully protect your js code, but they can sure piss off someone who is trying to "steal" your code.

Update:

I recently came across a very interesting article written by Patrick Weid on how to hide your js code, and he reveals a different approach: you can encode your source code into an image! Sure, that's not bullet proof either, but it's another fence that you could build around your code.
The idea behind this approach is that most browsers can use the canvas element to do pixel manipulation on images. And since the canvas pixel is represented by 4 values (rgba), each pixel can have a value in the range of 0-255. That means that you can store a character (actual it's ascii code) in every pixel. The rest of the encoding/decoding is trivial.
Thanks, Patrick!

The only thing you can do is obfuscate your code to make it more difficult to read. No matter what you do, if you want the javascript to execute in their browser they'll have to have the code.

Just off the top of my head, you could do something like this (if you can create server-side scripts, which it sounds like you can):

Instead of loading the script like normal, send an AJAX request to a PHP page (it could be anything; I just use it myself). Have the PHP locate the file (maybe on a non-public part of the server), open it with file_get_contents, and return (read: echo) the contents as a string.

When this string returns to the JavaScript, have it create a new script tag, populate its innerHTML with the code you just received, and attach the tag to the page. (You might have trouble with this; innerHTML may not be what you need, but you can experiment.)

If you do this a lot, you might even want to set up a PHP page that accepts a GET variable with the script's name, so that you can dynamically grab different scripts using the same PHP. (Maybe you could use POST instead, to make it just a little harder for other people to see what you're doing. I don't know.)

EDIT: I thought you were only trying to hide the location of the script. This obviously wouldn't help much if you're trying to hide the script itself.

http://code.google.com/closure/">Google Closure Compiler, http://developer.yahoo.com/yui/compressor/">YUI compressor, http://code.google.com/p/minify/">Minify</a>;, http://dean.edwards.name/packer/">/Packer/</a>;... etc, are options for compressing/obfuscating your JS codes. But none of them can help you from hiding your code from the users.

Anyone with decent knowledge can easily decode/de-obfuscate your code using tools like http://jsbeautifier.org/">JS Beautifier. You name it.

So the answer is, you can always make your code harder to read/decode, but for sure there is no way to hide.

From my knowledge, this is not possible.

Your browser has to have access to JS files to be able to execute them. If the browser has access, then browser's user also has access.

If you password protect your JS files, then the browser won't be able to access them, defeating the purpose of having JS in the first place.

Forget it, this is not doable.

No matter what you try it will not work. All a user needs to do to discover your code and it's location is to look in the net tab in firebug or use fiddler to see what requests are being made.

I think the only way is to put required data on the server and allow only logged-in user to access the data as required (you can also make some calculations server side). This wont protect your javascript code but make it unoperatable without the server side code

I agree with everyone else here: With JS on the client, the cat is out of the bag and there is nothing completely foolproof that can be done.

Having said that; in some cases I do this to put some hurdles in the way of those who want to take a look at the code. This is how the algorithm works (roughly)

1. The server creates 3 hashed and salted values. One for the current timestamp, and the other two for each of the next 2 seconds. These values are sent over to the client via Ajax to the client as a comma delimited string; from my PHP module. In some cases, I think you can hard-bake these values into a script section of HTML when the page is formed, and delete that script tag once the use of the hashes is over The server is CORS protected and does all the usual SERVER_NAME etc check (which is not much of a protection but at least provides some modicum of resistance to script kiddies).

2. Also it would be nice, if the the server checks if there was indeed an authenticated user's client doing this

3. The client then sends the same 3 hashed values back to the server thru an ajax call to fetch the actual JS that I need. The server checks the hashes against the current time stamp there... The three values ensure that the data is being sent within the 3 second window to account for latency between the browser and the server

4. The server needs to be convinced that one of the hashes is matched correctly; and if so it would send over the crucial JS back to the client. This is a simple, crude "One time use Password" without the need for any database at the back end.

5. This means, that any hacker has only the 3 second window period since the generation of the first set of hashes to get to the actual JS code.

6. The entire client code can be inside an IIFE function so some of the variables inside the client are even more harder to read from the Inspector console

   This is not any deep solution: A determined hacker can register, get an account and then ask the server to generate the first three hashes; by doing tricks to go around Ajax and CORS; and then make the client perform the second call to get to the actual code -- but it is a reasonable amount of work.

Moreover, if the Salt used by the server is based on the login credentials; the server may be able to detect who is that user who tried to retreive the sensitive JS (The server needs to do some more additional work regarding the behaviour of the user AFTER the sensitive JS was retreived, and block the person if the person, say for example, did not do some other activity which was expected)

An old, crude version of this was done for a hackathon here: http://planwithin.com/demo/tadr.html That wil not work in case the server detects too much latency, and it goes beyond the 3 second window period

As I said in the comment I left on gion_13 answer before (please read), you really can't. Not with javascript.

If you don't want the code to be available client-side (= stealable without great efforts), my suggestion would be to make use of PHP (ASP,Python,Perl,Ruby,JSP + Java-Servlets) that is processed server-side and only the results of the computation/code execution are served to the user. Or, if you prefer, even Flash or a Java-Applet that let client-side computation/code execution but are compiled and thus harder to reverse-engine (not impossible thus).

Just my 2 cents.

You can also set up a mime type for application/JavaScript to run as PHP, .NET, Java, or whatever language you're using. I've done this for dynamic CSS files in the past.

I know that this is the wrong time to be answering this question but i just thought of something

i know it might be stressful but atleast it might still work

Now the trick is to create a lot of server side encoding scripts, they have to be decodable(for example a script that replaces all vowels with numbers and add the letter 'a' to every consonant so that the word 'bat' becomes ba1ta) then create a script that will randomize between the encoding scripts and create a cookie with the name of the encoding script being used (quick tip: try not to use the actual name of the encoding script for the cookie for example if our cookie is name 'encoding_script_being_used' and the randomizing script chooses an encoding script named MD10 try not to use MD10 as the value of the cookie but 'encoding_script4567656' just to prevent guessing) then after the cookie has been created another script will check for the cookie named 'encoding_script_being_used' and get the value, then it will determine what encoding script is being used.

Now the reason for randomizing between the encoding scripts was that the server side language will randomize which script to use to decode your javascript.js and then create a session or cookie to know which encoding scripts was used then the server side language will also encode your javascript .js and put it as a cookie

so now let me summarize with an example

PHP randomizes between a list of encoding scripts and encrypts javascript.js then it create a cookie telling the client side language which encoding script was used then client side language decodes the javascript.js cookie(which is obviously encoded)

so people can't steal your code

but i would not advise this because

1. it is a long process
2. It is too stressful

use nwjs i think helpful it can compile to bin then you can use it to make win,mac and linux application