Convert JSF**k to normal JS

Question

Many of you already know JSF**k. For those who don't, it's a script that basically turns any JavaScript code into something written using only []()!+.

Your task is to build, using any language of your choice, a program which converts JSF**k into unobfuscated JavaScript.

• Input: A string with valid JSF**k code.
• Output: A string with the regular JavaScript code that has been previously JSF**ked to generate the input.

For this challenge, consider that the input string has only been JSF**ked once.

This is a code-golf contest, so the shortest code, in bytes, wins.

Answer 1

Javascript - 68 55 51

alert(/\n(.+)/.exec(eval(prompt().slice(0,-2)))[1])

Alternatively: (same length)

alert(/.+(?=\n})/.exec(eval(prompt().slice(0,-2))))

Runs in the console of your browser. Only guaranteed to work with code generated by jsfuck.com with the 'Eval Source' option ticked.

Ungolfed:

alert(
    /\n(.+)/.exec(                 // regex to extract code from inside outer function braces {}
        eval(prompt().slice(0,-2)) // remove the final set of parens () and evaluate the code
                                   // this results in a function, which will be converted to a string as 'exec' expects a string
    )[1]                           // get the first capture group
)

Answer 2

JavaScript, 122, works with any input

s=prompt().slice(0,-2)
i=s.length
while(i--){if((l=s.slice(i)).split(')').length==l.split('(').length)break}alert(eval(l))

Pretty simple; it just goes back in the string until the parentheses (( and )) are balanced. The last three characters of the JSF output are always )(), so slicing off the last 2 parens and then finding the matching paren for the other will always work. (It works with input with [] too.)