interface stable
interface OperatorFunction<T, R> extends UnaryFunction, Observable> {
  // inherited from index/UnaryFunction
  (source: T): R
} MonoTypeOperatorFunction 
    © 2015–2018 Google, Inc., Netflix, Inc., Microsoft Corp. and contributors.
Code licensed under an Apache-2.0 License. Documentation licensed under CC BY 4.0.
    https://rxjs.dev/api/index/interface/OperatorFunction