to return the mock data from Observable in angular service

 to return the mock data from Observable in angular service

Error Message: Generic type 'Observer<T> requires 1 type argument(s)

getDropdownData(request: string): Observable<DropdownData[]>{

const params = new HttpParams().append('request', request);

return this.http.get<DropdownData[]>(this.rootURL +'Home/DropdownData', { params });

let data: DropdownData[] = [

{

'label': 'Circle',

'Id': '10'

},

{

'label': 'Rectangle',

'Id': '20'

},

{

'label': 'Triangle',

'Id': '30'

},

{

'label': 'Pentagone',

'Id': '40'

}

];

return new Observable((observer: Observer<DropdownData[]>) => {

observer.next(data);

observer.complete();

});

}