Sets the handler that is invoked for every incoming message.
The handler is invoked in the Zone.root zone. If the handler should be invoked in the current zone, do:
rawPort.handler = Zone.current.bindCallback(actualHandler);
The handler must be a function which can accept one argument
of the type of the messages sent to this port.
This means that if it is known that messages will all be Strings,
a handler of type
void Function(String) can be used.
The function is invoked dynamically with the actual messages,
and if this invocation fails,
the error becomes a top-level uncaught error in the Zone.root zone.
// TODO(44659): Change parameter type to `void Function(Never)` to only // accept functions which can be called with one argument. void set handler(Function? newHandler);