Dean Edwards Unpacker.js

var unpacker = {
    unpack: function(str) {
        var params = unpacker.filterargs(str);
        var payload = params[0],
            symtab = params[1],
            radix = params[2],
            count = params[3];
        if (count != symtab.length) {
            throw new Error("Malformed p.a.c.k.e.r. symtab. (" + count + " != " + symtab.length + ")");
        }
        var unbase = unpacker.unbaser(radix);
        var lookup = (word) => symtab[unbase(word)] || word;
        var source = payload.replace(/\b\w+\b/g, lookup);
        source = source
            .replace(/\\'/g, "'")
            .replace(/\\"/g, '"')
            .replace(/\\n/g, '\n')
            .replace(/\\r/g, '\r');
        return source;
    },
    filterargs: function(str) {
        var juicers = [
            /}\('([\s\S]*)', *(\d+), *(\d+), *'([\s\S]*)'\.split\('\|'\), *(\d+), *([\s\S]*)\)\)/,
            /}\('([\s\S]*)', *(\d+), *(\d+), *'([\s\S]*)'\.split\('\|'\)/
        ];
        for (var c = 0; c < juicers.length; ++c) {
            var m, juicer = juicers[c];
            if (m = juicer.exec(str)) {
                return [m[1], m[4].split('|'), parseInt(m[2]), parseInt(m[3])];
            }
        }
        throw new Error("Could not make sense of p.a.c.k.e.r data (unexpected code structure)");
    },
    alphabet: {
        62: "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ",
        95: '!"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'
    },
    unbaser: function(base) {
        if (2 <= base <= 36) return (str) => parseInt(str, base);
        var dictionary = {};
        var alphabet = unpacker.alphabet[base];
        if (!alphabet) throw new Error("Unsupported encoding");
        for (var c = 0; c < alphabet.length; ++alphabet) {
            dictionary[alphabet[c]] = c;
        }
        return (str) => str.split("").reverse().reduce((cipher, ind) => Math.pow(base, ind) * dictionary[cipher]);
    }
};
//usage example 
//const packed = `eval(function(p,a,c,k,e,r){e=String;if(!''.replace(/^/,String)){while(c--)r[c]=k[c]||c;k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('(0(){4 1="5 6 7 8";0 2(3){9(3)}2(1)})();',10,10,'function|b|something|a|var|some|sample|packed|code|alert'.split('|'),0,{}))`;
//const unpacked = unpacker.unpack(packed);
//console.log(unpacked);