Third party modules constructor function properties become read-only in JPM

Question

I'm attempting to build an add-on for Firefox using the JPM utility. If I place the following in index.js, 'bar' is echoed out into the Browser Console without any issues

'use strict';

function Foo() {
    this.$data = false;
}

Foo.prototype.change = function(data) {
    this.$data = data;
};

var Test = new Foo();

Test.change('bar');

console.log(Test.$data);

But if I place the following in a file called test.js

'use strict';

function Foo() {
    this.$data = false;
}

Foo.prototype.change = function(data) {
    this.$data = data;
};

module.exports = new Foo;

and require it from index.js

var Foo = require('js/test');
Foo.change('bar');

I get a TypeError complaining that $data is read-only. How can I require third-party modules that use constructor function properties?

Answer 1

I guess this happens due to security reasons.

Anyway, export the Foo constructor and create the Foo object at the scope of index.js