Creator here. Yes it's a wrapper around the Web Worker and Node Worker Threads API. In order to create an inline worker, the user provided function is serialized using .toString() and any provided yield statements (which specify outside variables, functions & imports) are extracted. Because JavaScript objects are passed by reference, we can get the references by running the user function on the main thread first (iterating over each yield statement), and stop on the last yield so the main thread doesn't execute the rest of the function. Then, whenever a thread mutates a shared variable, the new value is send or transfered to the main thread, which then updates the variable using the object's reference.