Small utility decorator for typescript and rxjs. It wraps method into stream that emits data when original function is called.

InvokeListener.ts

import { Subject } from 'rxjs/Subject';

export default function InvokeListener<T>(): MethodDecorator {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    const original = descriptor.value;
    const emitter$ = new Subject<T>();

    const ngOnDestroy = target.ngOnDestroy;
    target.ngOnDestroy = function () {
      emitter$.complete();

      if (ngOnDestroy) {
        ngOnDestroy.call(this);
      }
    };

    let isApplied = false;

    descriptor.value = function (arg: T) {
      if (!isApplied) {
        original.call(this, emitter$);
        isApplied = true;
      }
      emitter$.next(arg);
    };
  };
}