Default at 3 workers. (Most processors today on both desktop and mobile are quad-core, => 1 main thread + 3 workers). Spawn them immediately.
An actor is a single function. Prototype additions are not taken into account (not straightforward to serialise). It behaves like a function, but async: arguments you give to the actor are passed through unaltered (but they must comply with the serialisation restrictions).
There's two ways to signify completion and both are bubbled up as events:
return something;
and this.done(something);
. The something
argument is