title: TypeScript : Cannot invoke an expression whose type lacks a call signature
body: <p>I am new to typescript. Basically I have a typescript GET function where I want to pass an ID to get that particular record back. I am getting this error on the return line. I researched this before posting here but could not get something close to my scenario. Help appreciated!</p>
  
  <blockquote>
    <p>Error TS2349  Cannot invoke an expression whose type lacks a call
    signature.</p>
  </blockquote>
  
  <pre><code>private getRecordRequestUrl = 'http://localhost/Service/api/ReservationRequest/GetRequestById';
  
   getRecordRequest(RequestId: number): Promise&lt;ReservationModel[]&gt; {
          return this.http.get(this.getRecordRequestUrl(RequestId))
              .toPromise()
              .then(response =&gt; response.json().Data as ReservationModel[])
              .catch(this.handleError);
  }
  </code></pre>