How to mangle JavaScript strings using hexadecimal escape?

Question

I need to mangle (obfuscate) JavaScript strings using hexadecimal encoding.

Source code:

var a = 'a';

Mangled code:

var a = '\x61';

It is easy to convert string to a hexadecimal value:

var map = {
    '\b': '\\b',
    '\f': '\\f',
    '\n': '\\n',
    '\r': '\\r',
    '\t': '\\t',
};

var hex = function (str) {
    var result = '';
    for (var i = 0, l = str.length; i < l; i++) {
        var char = str[i];
        if (map[char]) {
            result += map[char];
        } else if ('\\' == char) {
            result += '\\' + str[++i];
        } else {
            result += '\\x' + str.charCodeAt(i).toString(16);
        }
    }
    return result;
};

But when I add this string to the output file I get:

var a = '\\x61';

P.S. I use esprima/escodegen/estraverse to work with AST.

See how the strings are converted here: http://stackoverflow.com/questions/21647928/javascript-unicode-string-to-hex — Michael Antipin, Apr 01 '16 at 13:14
Note `\x??` is a one-byte character, while `\u????` is a unicode character. It's likely safer to use the latter. — Michael Antipin, Apr 01 '16 at 13:16
This version is perhaps closer to what you need: https://gist.github.com/mathiasbynens/1243213 — Michael Antipin, Apr 01 '16 at 13:21
@NoxNoctis Thanks. I could not find code that solves my issue. The issue is escaping of '\' character during output to file. — alpha, Apr 01 '16 at 16:38
@КачаловТимофей no, I didn't. Ping me, if you will find it ) — alpha, May 02 '16 at 14:14
solution: https://github.com/estools/escodegen/issues/293 last comment. — Качалов Тимофей, May 02 '16 at 17:12

score 2 · Answer 1 · edited May 23 '17 at 10:33

Below is an draft of implementation based on Качалов Тимофей's solution:

var esprima = require('esprima');
var estraverse = require('estraverse');
var escodegen = require('escodegen');

function stringToUnicode(string) {
    return '"' + string.replace(/[\s\S]/g, function (escape) {
       return '\\u' + ('0000' + escape.charCodeAt().toString(16)).slice(-4);
    }) + '"';
}

var tree = esprima.parse(code);
//...
estraverse.replace(tree, {
    leave: function(node){
        if (node.type === 'Literal' && (node.raw[0] === '"' || node.raw[0] === '\'' )){
            node['x-verbatim-property'] = {
                content : stringToUnicode(node.value),
                precedence: escodegen.Precedence.Primary
            };
        }
    }
});
//...
var result = escodegen.generate(tree, {verbatim: 'x-verbatim-property'});

How to mangle JavaScript strings using hexadecimal escape?

1 Answers1