Implementing observable fails

Am trying to implement observable with the following class

import {Injectable, } from '@angular/core';
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/share';
import {Observer} from 'rxjs/Observer';

export class CalendarService {

    dataChange: Observable<any>;
    dataChangeObserver: Observer<any>;

    constructor() {
        this.dataChange = new Observable((observer) => {
            this.dataChangeObserver = observer;

    setDate(date: any) {;

When calling setDate() with a value am getting the following error

ORIGINAL EXCEPTION: TypeError: Cannot read property ‘next’ of undefined
TypeError: Cannot read property ‘next’ of undefined

It seems that this.dataChangeObserver is not defined, am I missing something?

So i created this issue: