script.js file
ScriptHost
A ScriptHost object represents a Worker script in the Main thread.
A ScriptHost object (defined in script.js) runs in the
Main Javascript thread. It starts a Worker via host.js
which creates a WorkerHost object in the Worker thread. The
ScriptHost<->WorkerHost objects bridge needed API from the Main
thread to the Worker thread. The WorkerHost then loads and calls into a
user provided ES Module, the actual user script which communicates via
the WorkerHost global variable host. See also
#WorkerHost.