codethief's JSFuck compiler

Compile any JavaScript code to JSFuck, i.e. to fully equivalent JavaScript code that only consists of characters in the set ()[]!+.

This code was written within a handful of hours on a late Thursday night in June 2022 during which I was trying to reverse-engineer and understand some of the posts in the original thread. In particular, since the solutions there usually only went as far as reproducing / JSFuck-encoding eval() (or Function()), I was interested in how any character could be encoded. Put differently: How could I get to String.fromCodePoint() as quickly as possible?

Only once I was almost through with writing this code I realized that there's jsfuck.com that comes with rather detailed explanations of how JSFuck works and lots of additional tricks that I hadn't known. Oh well. It was a fun exercise at the very least.

Running this

Just copy & paste the code into your browser's console and, afterwards, invoke compile("<Your JS code>"). Note that your browser needs to support Array.prototype.at() or otherwise the compiler's code would need to be modified slightly (see comments).

A note regarding style

This code is messy and entirely linear for a reason. The point was not to write a compiler with beautifully organized yet difficult to understand code, nor was the goal to write a compiler like JSFuck.com that minimizes output length as far as possible.

Rather, the goal was to get to a fully working compiler (that's able to compile arbitrary JavaScript code containing any Unicode characters) in as short a time as possible, using as few tricks and techniques as possible.

Moreover, I also wanted to understand how exactly the different techniques depended and built upon one another. This is one reason why I made extensive use of variables and JavaScript's template literal syntax and of non-hoisted functions (const f = () => { … }), so that I could see the precise cross-code dependencies and also make sure (through linting) that dependencies never remained unresolved and everything got defined in the right order.

All in all, it's a collection of arcane techniques and tricks that you're supposed to read from top to bottom until they culminate in a very simple compile() function. One might say it's an example of (probably bad) literal programming.