Without going into details about why the above doesn't work: what you are trying to achieve is multi-threading in JavaScript. That does not exist. JavaScript is a single-threaded language by design. Concurrency is asynchronous. And V8, like all other JS VMs, is a single-threaded engine. The only way multiple threads can access the same isolate is through a global mutax (cf. the Locker class).
In short, trying to approach JavaScript with a programming approach based on multi-threading won't get you anywhere. It's not how it works.