JSFuck – esoteric JavaScript

Does knowing any of this make you a better programmer? I'd say no.

Should you be using any of this in production code? No

The next programmer even if he is a really good one might not know that particular esoteric trick.

I'm not trying to vote down or anything, but what is the point? Most of it look like language design warts to me. Most of them should have thrown exceptions and errored out.

Now I'm loving the idea of static typing a lot more.

Here's a slightly more entertaining version of the discrepancies/oddities found in javascript:

https://www.destroyallsoftware.com/talks/wat

A bunch of that is wrong or at least misleading.

> {} + [] > 0 (The number zero)

This is wrong, it is only true in the weird scenario that you type it into the jsconsole and don't use the result. It parses as an empty block ({}) and then an unrelated unary +[] after that. var x = {} + []; gives you a string and it is the same as var x = [] + {}.

There is more logic than it seems here:

  Unary plus:
  > always gives a number (a double: NaN is a double)
  > on array: +a -> if len>=2: NaN else +a[0] (recursively)
  > on object: NaN
  > on string: parseNumber, or NaN if that fails
  > on bool: 0 for false, 1 for true
  > on null: 0
  > on undefined: NaN

  binary plus (addition):
  > order doesn't matter except for the jsconsole pseudo-bug
  > if both sides are number or boolean, add them
  > else, toString() both sides and concat them

  boolean negate (not):
  > false for 0, false, "", null, undefined
  > true otherwise

  binary - (subtraction)
  > x-y coerces x and y to number and subtracts them.
  > Most mainstream languages that use + for string concat don't use - for some sort of string unconcat so its not too crazy.

  > typeof [] === typeof {}

  This isn't so crazy, typeof any non-primitive gives you "object".
  [] is pretty much just an object plus magic .length property,
  var x = []; x.blah = 7; console.log(x.blah) works. It doesn't work on number or bool.

Yeah, it wasn't the greatest idea to copy and paste the minified version of jQuery in there...

Yes, but if you gzip it, you should get a much smaller file.

Well ; produces 8307 chars on its own (without eval checked) -- which seems kind of inefficient (for such a common character in idiomatic javascript). Looking that their encoder, ';' actually has a specific encoding (which itself has to be encoded) so it looks like there's some inefficient expansion taking place (e.g. '.' has a specified encoding that does not require recursive encoding). Encoding the string "link" in the expansion of ';' appears to be very expensive -- alert is cheap in comparison because you can obtain its letters from Javascript return values (e.g. "l" is pulled out of "false" which is obtained by (![]+"")[2])

I'd imagine that if you were serious about this, you'd implement, say, e=String.fromCharCode (12k chars) and use that to dig yourself out of a lot of this expensive stuff if you need more than one hard-to-encode character.

That's the joke. It's a strict subset of JS, not a transpiled language.

This article is pretty good on piecing it stuff like this together: https://blog.korelogic.com/blog/2015/01/12/javascript_deobfu...

Once you have partial evaluation, it's really easy. I've done this (and with jsfuck too!) http://m1el.github.io/jsdeobfuscate/

Just remove the () and you'll get the code in a string.

Most JavaScript developers have tiny computers.

What do you mean two characters? What are they exactly? I'm guessing $ and ; because it's like jQuery but some operations seem impossible, like how does it even assign variables?