How can I obfuscate protect JavaScript

Question

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

User · Answer

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.

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

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

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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  amp  Encoder

User · Answer

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

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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

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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

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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

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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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

This one minifies but doesn t obfuscate  If you don t want to use command line Java you can paste your javascript into a webform

User · Answer

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.

User · Answer

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

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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

User · Answer

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

User · Answer

If you use a JavaScript library  consider Dojo Toolkit which is compatible  after minor modifications  with the Closure Compiler s Advanced mode compilation   Dojo     The Only JavaScript Library  Compatible with The Closure Compiler  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

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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    lt  php  t1 apache request headers    if base64 encode   SERVER  HTTP REFERER      aHR0cDovL2hlcmUuaXMvbXkvbGF1bmNoZXIuaHRtbA    amp  amp   POST  Troll2     lol  amp  amp  t1  Troll1    lol     echo  ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg      here is the SECRET javascript code  else   echo  d2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs         gt    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   lt  doctype html gt  lt html gt  lt head gt  lt meta charset  utf-8  gt  lt title gt  lt  title gt  lt script src  data application javascript base64 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  gt  lt  script gt  lt  head gt  lt body gt  lt  body gt  lt  html gt    Troll php   lt  php  t1 apache request headers   if   base64 encode   SERVER  HTTP REFERER      PUT THE LAUNCHER REFERER HERE  amp  amp     POST  Troll2     lol  amp  amp  t1  Troll1    lol   echo  ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg     else echo  d2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs        gt

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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    lt  php  t1 apache request headers    if base64 encode   SERVER  HTTP REFERER      aHR0cDovL2hlcmUuaXMvbXkvbGF1bmNoZXIuaHRtbA    amp  amp   POST  Troll2     lol  amp  amp  t1  Troll1    lol     echo  ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg      here is the SECRET javascript code  else   echo  d2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs         gt    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   lt  doctype html gt  lt html gt  lt head gt  lt meta charset  utf-8  gt  lt title gt  lt  title gt  lt script src  data application javascript base64 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  gt  lt  script gt  lt  head gt  lt body gt  lt  body gt  lt  html gt    Troll php   lt  php  t1 apache request headers   if   base64 encode   SERVER  HTTP REFERER      PUT THE LAUNCHER REFERER HERE  amp  amp     POST  Troll2     lol  amp  amp  t1  Troll1    lol   echo  ZG9jdW1lbnQuYm9keS5hcHBlbmRDaGlsZChkb2N1bWVudC5jcmVhdGVFbGVtZW50KCdkaXYnKSkuaW5uZXJUZXh0PSdBd2Vzb21lJzsNCg     else echo  d2luZG93Lm9wZW4oJycsICdfc2VsZicsICcnKTt3aW5kb3cuY2xvc2UoKTs        gt

User · Answer

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 more than 10 years ago  and YUI is no longer maintained  Google Closure Compiler is still in use  and UglifyJS can be run locally via node package manager  npm install -g uglify-js  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

User · Answer

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 more than 10 years ago  and YUI is no longer maintained  Google Closure Compiler is still in use  and UglifyJS can be run locally via node package manager  npm install -g uglify-js  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

User · Answer

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

User · Answer

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

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This one minifies but doesn t obfuscate  If you don t want to use command line Java you can paste your javascript into a webform

User · Answer

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

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If you use a JavaScript library  consider Dojo Toolkit which is compatible  after minor modifications  with the Closure Compiler s Advanced mode compilation   Dojo     The Only JavaScript Library  Compatible with The Closure Compiler  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

User · Answer

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

User · Answer

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

User · Answer

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.

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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

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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

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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

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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

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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  amp  Encoder

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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 more than 10 years ago  and YUI is no longer maintained  Google Closure Compiler is still in use  and UglifyJS can be run locally via node package manager  npm install -g uglify-js  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

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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

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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.

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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

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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

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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

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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

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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

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This one minifies but doesn t obfuscate  If you don t want to use command line Java you can paste your javascript into a webform

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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

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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

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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

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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

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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

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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

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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

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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

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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 more than 10 years ago  and YUI is no longer maintained  Google Closure Compiler is still in use  and UglifyJS can be run locally via node package manager  npm install -g uglify-js  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

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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

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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

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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

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This one minifies but doesn t obfuscate  If you don t want to use command line Java you can paste your javascript into a webform

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

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