Basic info:

• Node.js version: v12.9.0
• jsdom version: v15.2.0

Minimal reproduction case

const { JSDOM } = require("jsdom");
const dom = new JSDOM('');
console.log(dom.window.Navigator); // Expected: Navigator() { ... }, Actual: undefined

https://runkit.com/pmdartus/5da6b38cfc8b010013f7ed47

How does similar code behave in browsers?

https://jsfiddle.net/ab3zy6ek/

Details

This can be solved by exporting the generated Navigator interface out of lib/jsdom/living/index.js.