Is it possible to encode JavaScript with masked binary values?

This segment of code produces the output D. The real question is - HOW?

alert([][(![]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[!+[]+!+[]]]()[([][(![]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(![]+[])[!+[]+!+[]]]()+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(...

I comprehend that ![] equates to either false or 0, but how does it actually run? And more importantly, is there a way to translate this into something understandable by humans and not just Jon Skeet?

Could someone dissect a portion of this code and explain what exactly is going on?

javascriptobfuscation

Answer №1

Upon dissecting the given expression, it eventually boils down to:

[]['sort']['call']()["btoa"]("00")[1]; // "D"

This can be simplified as:

btoa("00")[1]; // "D"

How does one go about "decoding" it?

The key lies in understanding the operators used. Firstly, an array literal is employed, followed by multiple bracket notation property accesses and a couple of function invocations.

But how does it all come together?

The secret lies in stringing together various type conversions. For instance, to retrieve the letter f:

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

Breaking it down, ![]+[], results in a boolean negation returning false because arrays are truthy, followed by concatenation producing the string "false". Then, applying brackets to that string for character access alongside +[] turning into 0.

+[] yields zero due to the Array's toString method resulting in an empty string for an empty array which converts to zero when coerced into a number (via the unary + operator here).

Such trickerations continue with things like generating strings - "true", "false", "null", "undefined", etc., and techniques to obtain numeric values.

For instance, numerical values required for character access are acquired through cryptic type conversions as shown below:

+[];            // 0, equal to +""
+!+[];          // 1, equal to +true
!+[]+!+[];      // 2, equal to +true+true
!+[]+!+[]+!+[]; // 3, equal to +true+true+true

Answer №2

This script utilizes some clever tricks involving JavaScript type conversions. As pointed out by CMS, it is essentially equivalent to: 

[]['sort']['call']()["btoa"]("00")[1];

Strings are assembled by extracting them from values such as false, among others.

For instance, to obtain the character s in the word "sort":

Create a "false": (![]+[]) -- where ![] yields false and +[] converts it to a string.

To retrieve the value 3 using: !+[]+!+[]+!+[] - each !+[] resolves to true, but adding booleans results in an integer representation. For example, true + true = 2

To access the s utilizing string index notation ("false"[3] = 's'): (![]+[]) [!+[]+!+[]+!+[]]

You now have an s. This process is repeated until enough characters are assembled to access the desired method or property.

Answer №3

The concept of truthiness in JavaScript can be quite perplexing. For example, when you add an empty array to the negation operator, it results in 'false'. However, converting that empty array to a number with +[] actually returns 0, making the expression true. JavaScript's implicit type conversions definitely make for some interesting behavior!

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