title: How to return Observable after some Promise get resolved in Ionic 2/Angular 2?
body: <p>I am trying to return an observable after a successful completion of my Promise, but that function is not returning Observable. 
  To be specific to code, i want to fetch auth token from storage (returns promise) and after that data got fetched then generate a Post request to Api (returns Observable). By doing so, sublime text gives an error on function that "a function whose declared type is neither 'void' nor 'any' must return a value"
  below is my code,</p>
  
  <pre><code>logout() : Observable&lt;any&gt;{
    this.userData.getAuthToken().then((token)=&gt;{
      this.token = token;
      this.headers = new Headers ({
        "X-USER-TOKEN": token
      });
      this.options = new RequestOptions ({
        headers: this.headers
      });
      var logout_url = "Api logout method";
      return this.http.post(logout_url,{},this.options)
        .map (res =&gt; res.json())
    });
  }
  </code></pre>
  
  <p>if i simply do a post request then it returns fine like this</p>
  
  <pre><code>return this.http.post(logout_url,{},this.options)
    .map (res =&gt; res.json())
  </code></pre>
  
  <p>but when i try to fetch data it do not return value from this post request.
  Any help will be much Appreciated! Thanks in advance  </p>