Perverted JavaScript... checking for access violations based on member prefixing!

Guard.js

/**
 * Copyright (c) 2011 Ivo Wetzel.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

(function(exports) {

    var protectId = 0;

    function guard(clas, raise) {

        var e = function() {};
        e.prototype = clas.prototype;
        e.prototype.constructor = clas;

        return function() {

            var instance = new e();
            clas.apply(instance, arguments);
            shield(instance, clas, raise);
            return instance;

        };

    }

    function shield(obj, clas, raise) {

        var proto = clas.prototype;

        function accessViolation(key, f, type, value) {

            var detail = value ? key + ' (' + value + ')' : key,
                msg = 'Access violation [' + type + ': ' + detail + '] on ';

            f = f ? f.caller || window : window;

            var error = new AccessError(f, msg, type, obj, f, value);
            if (raise) {
                throw error;
            }

        }

        function protectProperty(key, read) {

            var stored = obj[key];
            Object.defineProperty(obj, key, {

                configurable: false,
                enumerable: !read,

                set: function sf(value) {
                    if (clas.___protectId !== sf.caller.___protectId) {
                        accessViolation(key, sf, 'write', value);
                    }
                    stored = value;
                },

                get: function gf() {
                    if (read && clas.___protectId !== gf.caller.___protectId) {
                        accessViolation(key, gf, 'read', stored);
                    }
                    return stored;
                }

            });

        }

        function protectMethod(proto, method) {

            var func = proto[method];
            Object.defineProperty(obj, method, {

                configurable: false,
                enumerable: false,

                get: function f(value) {
                    if (clas.___protectId !== f.caller.___protectId) {
                        accessViolation(method, f, 'call');
                    }
                    return func;
                }

            });

        }

        // Protect properties
        for(var prop in obj) {
            if (obj.hasOwnProperty(prop)) {

                var sub = prop.match(/^_+/),
                    level = sub && sub[0].length;

                if (level >= 1) {
                    protectProperty(prop, level === 2);
                }

            }
        }

        // Patch the prototype once for each clas
        if (clas.___protectId === undefined) {

            clas.___protectId = protectId++;

            for(var method in proto) {
                if (proto.hasOwnProperty(method)) {

                    proto[method].___protectId = protectId;

                    if (/^__/.test(method)) {
                        protectMethod(proto, method);
                    }

                }
            }

        }

    }

    function AccessError(func, msg, type, object, caller, value) {

        this.name = 'AccessError';
        this.message = '';
        this.object = object;
        this.type = type;
        this.caller = caller;
        this.value = value;

        console.error(msg, 'on', object, 'by', caller);

        if (Error.captureStackTrace) {
            Error.captureStackTrace(this, func);
        }

    }

    AccessError.prototype = new Error();

    exports.guard = guard;

})(typeof window !== 'undefined' ? window : global);




function Kitten() {
    this.__foo = 2;
    this.__private = 16;
}

function Foo() {


    this.Public = 2;
    this.__private = 32;
    this._protected = 'blue';

    Kitten.call(this);

    // Valid
    this.__private = 64;
    this._protected = 'red';
    this.__privateMethod(this.__private);

}

Foo.prototype = {

    // Valid access from within the object
    test: function() {
        console.log('test');
        this.__setStuff(15, 'yellow');
        return this.__private + this._protected;
    },

    __setStuff: function(a, b) {
        this.__private = a;
        this._protected = b;
    },

    __privateMethod: function(num) {
        console.log('Private random number ', num);
    },

    _protectedMethod: function() {

    }

};


function test() {

    var e = new Foo(),
        b = new Foo();

    e.test();

    var test = {
        l: e
    };

    // Valid read
    console.log(e._protected);

    // Invalid writes
    console.log('------- Invalid ----------');
    e.__private = 128;
    e._protected = 'green';

    // Invalid read
    console.log(e.__private);
    console.log(test.l._protected);
    console.log(test.l.__private);

    e.__privateMethod(4);

}

Foo = guard(Foo);
test();