A representation of any set of values over any amount of time.
The sink has completed. This function "closes" the sink.
An error that has occured. Calling this function "closes" the sink.
Besides the errors being
readonly GraphQLError, it
can also be a
CloseEvent, but to avoid bundling DOM typings because
the client can run in Node env too, you should assert the close event
type during implementation.
Next value arriving.