How to allow addon's content script access Javascript variables from the current tab?

Question

Supposed my add-on has to access a Javascript variable from a webpage. Let's take https://mozilla.org. There is a global variable called optimizelyCode. My addon will only work if this variable is accessible.

How do I let my pageMod do that?

To experiment, here are some tutorial scripts:

var widgets = require("sdk/widget");
var tabs = require("sdk/tabs");

var widget = widgets.Widget({
  id: "mozilla-link",
  label: "Mozilla website",
  contentURL: "http://www.mozilla.org/favicon.ico",
  onClick: function() {
    tabs.activeTab.attach({
      contentScriptWhen: 'end',
      contentScript:
        'console.log(optimizelyCode)'
        })
    }
});

and

var pageMod = require("sdk/page-mod");

pageMod.PageMod({
  include: "*.mozilla.org",
  contentScriptWhen: 'end',
  contentScript: 'console.log(optimizelyCode);'
});

I get Reference/Undefined error because optimizelyCode is not avaiaible to addon. In this example I am not even using content script file.

As far as I know, I can only access basic DOM stuff like getElementById that kind of methods. How can I access these webpage local JS variables?

Reference: https://developer.mozilla.org/en-US/Add-ons/SDK/Guides/Content_Scripts/Loading_Content_Scripts

Answer 1

Since this is add-on SDK, it uses a different syntax from the rest of Firefox, and you need to use unsafeWindow.optimizelyCode.