Multifile extensions with global variables that are not constant

[Amy C <mathematical coffee gmail com>]

I'm writing an extension with multiple .js files, but where some need
access to variables in others. These variables are not constant.

As an example, in the main `extension.js`, imagine the following occurs:

// load the other .js files, theme.js & toon.js
const Theme = Extension.theme;
const Toon = Extension.toon;

var theme = new Theme.Theme();
var toons = [];
for ( let i=0; i<10; ++i ) {
    toons.append( new Toon.Toon() );
}

In my situation, the Toon.Toon class needs access to the 'theme'
variable to get some information from it.
However if I just use 'theme.[property]' from within toon.js without
declaring theme first, this is a syntax error (understandably).

Is the only way to give the `Toon.Toon` class access to `theme` to
provide it in the initialiser?:
    toons.append( new Toon.Toon(theme) );

Or is it possible to put in the toon.js file something like
    const GLOBAL = (????); // any variables that are shared between
files live here
and then have `theme.js` populate `GLOBAL.theme` with a pointer to the
`theme` object, and have `toon.js` access (the updated!)
`GLOBAL.theme`?

cheers.