에러 전문: The 'this' context of type 'void' is not assignable to method's 'this' of type 'Observable'.ts(2684) No overload matches this call. Overload 1 of 11, '(op1: OperatorFunction, op2: OperatorFunction): Observable', gave the following error. Argument of type 'Observable' is not assignable to parameter of type 'OperatorFunction'. Type 'Observable' provides no match for the signature '(source: ..
