JScrewIt ·

Use JScrewIt to convert your JavaScript code into JSFuck. JSFuck is an encoding technique that uses only the six characters ! ( ) + [ ] to produce syntactically correct JavaScript that can still run in a browser or another JavaScript engine without any additional software.

Play now with jscrew.it, or give a look at jQuery Screwed for a true example: a working version of jQuery consisting of only six different characters.

JScrewIt was born as a fork of aemkei's JSFuck and has developed into one of the most powerful JSFuck encoders on the web, including a number of unique features.

• Options to optimize code for a particular set of JavaScript engines or even just for your browser: the more specific your engine choice, the shorter the code you'll get.
• Support for all modern JavaScript engines (and a few older ones, too).
• Neatly optimized large file encoding.
• Encode-as-you-type browser interface.

Example

The following source will do an alert(1) in any browser, including Internet Explorer:

[][(![]+[])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+
(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+!![]]][([+[![]]]+!!++([]+[][(![]+[])[+[]]+(
[![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![
]+!![]]+(!![]+[])[+!![]]])[+[]]+[][(![]+[])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![
]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+!![]]])[+!!
[]+[+!![]]]+(!!++([]+[][(![]+[])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+
!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+!![]]])[+[]]+[][(![]+[
])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])
[!![]+!![]+!![]]+(!![]+[])[+!![]]])[+!![]+[+!![]]]+([][[]]+[])[+!![]]+(![]+[])[!
![]+!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[+!![]]+([][[]]+[])[+[]]+([+[![]]]+!!++([
]+[][(![]+[])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]
]+(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+!![]]])[+[]]+[][(![]+[])[+[]]+([![]]+[][[
]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]]+(!
![]+[])[+!![]]])[+!![]+[+!![]]]+(!![]+[])[+[]]+(!!++([]+[][(![]+[])[+[]]+([![]]+
[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]
]+(!![]+[])[+!![]]])[+[]]+[][(![]+[])[+[]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[
!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+!![]]])[+!![]+[+!
![]]]+(!![]+[])[+!![]]]((!![]+[])[+!![]]+(!![]+[])[!![]+!![]+!![]]+(!![]+[])[+[]
]+([][[]]+[])[+[]]+(!![]+[])[+!![]]+([][[]]+[])[+!![]]+(+[]+[+[]]+[][(![]+[])[+[
]]+([![]]+[][[]])[+!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]
+!![]+!![]]+(!![]+[])[+!![]]])[+!![]+[+!!++([]+[][(![]+[])[+[]]+([![]]+[][[]])[+
!![]+[+[]]]+(![]+[])[!![]+!![]]+(!![]+[])[+[]]+(!![]+[])[!![]+!![]+!![]]+(!![]+[
])[+!![]]])[+[]]]]+(![]+[])[+!![]]+(![]+[])[!![]+!![]]+(!![]+[])[!![]+!![]+!![]]
+(!![]+[])[+!![]]+(!![]+[])[+[]])()(+!![])

Setup Instructions

In the Browser

To use JScrewIt in your project, download jscrewit.js (uncompressed, development version) or jscrewit.min.js (compressed, productive version) from npm and include it in your HTML file.

<script src="jscrewit.js"></script>

Alternatively, just hotlink the latest version on npm using a CDN of your choice.

<script src="https://cdn.jsdelivr.net/npm/jscrewit"></script>

In Node.js

If you are using Node.js, you can install JScrewIt with npm.

npm install jscrewit

Then you can import it in your code in the usual way.

import JScrewIt from "jscrewit"; // ECMAScript module syntax

or

const JScrewIt = require("jscrewit"); // CommonJS syntax

JScrewIt comes with bundled TypeScript declarations: you can use it in TypeScript without installing any additional packages.

Usage

Basics

This will encode the alert(1) example shown above and run it using eval.

const output = JScrewIt.encode("alert(1)");
eval(output);

To encode just a plain string rather than an executable script, enclose the text in double or simple quotes, like when introducing a string literal in JavaScript code.

const output = JScrewIt.encode("'Hello, world!'");
const input = eval(output); // input contains the string "Hello, world!".

We can also use escape sequences to encode newlines and other characters. Note that the initial backslash in an escape sequence must be escaped with another backslash when writing a "sting in a string".

const output = JScrewIt.encode("\"1.\\n2.\\n\\u263A\"");
/*
1.
2.
☺
*/

JScrewIt.encode also accepts an optional second parameter containing options that control various aspects of the encoding. These are covered in detail in the relative section in the API Reference.

Features

One peculiarity of JScrewIt is the ability to generate JSFuck code that is customized for a particular set of JavaScript engines (web browsers or Node.js). This optimized code is shorter than generic JSFuck code but does not work everywhere. To make use of this optimization, we have to specify which features the decoder engine is expected to support.

In order to understand how this works, let's consider the JavaScript functions atob and btoa. Not all browsers support these functions: without any further information, JScrewIt will assume that they are unavailable and will not use them to encode the input. However, if we know in advance that the browsers we plan to target do support atob and btoa, we can let JScrewIt create code that uses those functions whenever that makes the output shorter.

The way to tell JScrewIt to use a particular set of features is by specifying a value for the features option in the second parameter passed to encode.

For instance, a generic alert(1) example for an unspecified environment is 1903 chracters long.

const output = JScrewIt.encode("alert(1)"); // output is 1903 characters

We can save a few characters by indicating that our code is only supposed to run in a browser. We do this using the feature BROWSER.

const options = { features: "BROWSER" };
const output = JScrewIt.encode("alert(1)", options); // 1882 characters

But if we are only interested in code that runs in an up to date Firefox browser, the output length shrinks to about one third:

const options = { features: "FF" };
const output = JScrewIt.encode("alert(1)", options); // 655 characters now

Here we have used another feature: FF. This feature produces the shortest possible code that runs in current Firefox browsers.

We can specify more than one feature using an array, e.g.

const input = "document.body.style.background='red'";
const options = { features: ["ATOB", "WINDOW"] };
const output = JScrewIt.encode(input, options);

As opposed to the previous example, the features specified here refer to certain abilities that may be supported by more than one particular class of browsers or JavaScript engines. Specifically, ATOB indicates native support for the functions atob and btoa, while WINDOW refers to a particular string representation of the global object self, where available. The code generated by JScrewIt will run fine in engines that support both of these features. In engines that don't support both features, the code may not work, and may produce unpredictable results. Most typically, it will throw some kind of error at runtime.

It's important to keep in mind that each of the target engines needs to support every feature we specify. So if we want our JSFuck code to run in Android Browser 4.0, Safari 7.0 and Node.js 13+, we can only specify features supported by all of these engines. These features can be retrieved with JScrewIt.Feature.commonOf.

{ features: JScrewIt.Feature.commonOf("ANDRO_4_0", "NODE_13", "SAFARI_7_0") }

The features turn out to be ESC_HTML_QUOT, GMT, INCR_CHAR, NAME and NO_IE_SRC (a quick way to see this is entering JScrewIt.Feature.commonOf("ANDRO_4_0", "NODE_13", "SAFARI_7_0").toString() in the browser's console). With this knowledge, we could also rewrite the expression above as follows.

{ features: ["ESC_HTML_QUOT", "GMT", "INCR_CHAR", "NAME", "NO_IE_SRC"] }

Finally, note that simply specifying an array of engine features will not achieve the desired effect, as it will result in the union of the features available in every engine rather than in their intersection.

- { features: ["ANDRO_4_0", "NODE_13", "SAFARI_7_0"] }

Further Reading

• API Reference
• Feature Reference

Compatibility

JScrewIt itself and the code it generates are compatible with the JavaScript engines listed below.

  Chrome 122+   Safari 7.0+   Edge 122+   Firefox 90+   Opera 108+   Internet Explorer 9+   Android Browser 4.x   Node.js (all versions)

Engine Support Policy

Only the most recent stable version of Chrome, Edge, Firefox and Opera are guaranteed to be supported at any time, as detailed below.

• Chrome: (Current - 1) and Current
• Edge: (Current - 1) and Current
• Firefox: (Current - 1) and Current, ESR
• Opera: Current

Expect compatibility with these browsers to change in future releases of JScrewIt, while the current browser versions become replaced by newer ones.

Compatibility with older versions of Internet Explorer, Safari, Android Browser and Node.js is stable and not expected to change until the next major release of JScrewIt.

Known Limitations

Despite claims from other sources, not every piece of JavaScript can be converted into JSFuck. Some intrinsic limitations of the language make the code generated by JScrewIt unusable under certain conditions.

Modules

JScrewIt is designed to encode JavaScript scripts, as opposed to modules. Many module related features don't work at all in JSFuck: import and export statements in EcmaScript modules or usages of the require API in CommonJS modules cannot be encoded and are not supported.

Altered Global Objects

JavaScript libraries that manipulate global objects and functions can easily break the code generated by JScrewIt. There are many of them, so expect incompatibilities when working with third party tools.

Stack Trace Inspection

Stack traces thrown in encoded source files look different and may as well include frames not expected by the original code. For this reason, code that relies on stack trace inspection may no longer work after being converted.

Interesting Links

• JScrewIt online encoder
• JSFuck on Wikipedia
• JSFuck on Esolang
• jsfuck.com
• jQuery Screwed