description

# RegisterCallbackHandler typedef

RegisterCallbackHandler = ZoneCallback<R> Function<R>(Zone self, ZoneDelegate parent, Zone zone, R f())

The type of a custom Zone.registerCallback implementation function.

A function used as ZoneSpecification.registerCallback to specialize the behavior of a new zone.

Receives the Zone that the handler was registered on as `self`, a delegate forwarding to the handlers of `self`'s parent zone as `parent`, and the current zone where the error was uncaught as `zone`, which will have `self` as a parent zone.

The function `f` is the function which was passed to the Zone.registerCallback of `zone`.

The handler should return either the function `f` or another function replacing `f`, typically by wrapping `f` in a function which does something extra before and after invoking `f`

The function must only access zone-related functionality through `self`, `parent` or `zone`. It should not depend on the current zone (Zone.current).

## Implementation

    typedef RegisterCallbackHandler = ZoneCallback<R> Function<R>(
      Zone self,
      ZoneDelegate parent,
      Zone zone,
      R Function() f,
    );