title: Type 'Promise<string[]>' is not assignable to type 'string[]'
body: <p>Getting following error:
  <strong>Type 'Promise&lt;string[]&gt;' is not assignable to type 'string[]'.
  Property 'includes' is missing in type 'Promise&lt;string[]&gt;'.</strong></p>
  <p>when i cast Promise&lt;string[]&gt; to type 'string[]'
  My code below,</p>
  <p><strong>Component: app.dashboard.ts</strong></p>
  <pre class="lang-js prettyprint-override"><code>    import {Component} from '@angular/core';
      import { MemberService } from &quot;./app.service&quot;;
      @Component({
      selector:'app-root',
      templateUrl:'./app.dashboard.html',
      providers:[MemberService]
                })
  
      export class AppDashboard{
        title='Dashboard'
        constructor(private memberService: MemberService) { }
  
        public doughnutChartLabels:string[] = 
          this.memberService.getmemberheader();//error occurred here
        }
      }
  </code></pre>
  <p><strong>Service:app.service.ts</strong></p>
  <pre class="lang-js prettyprint-override"><code>    import { Injectable } from '@angular/core';
      import { Member } from './Member';
      import { Http, Response, Headers, RequestOptions, URLSearchParams } from'@angular/http';
      import 'rxjs/add/operator/map';
      import 'rxjs/add/operator/toPromise';
  
      @Injectable()
      export class MemberService
      {
        constructor(private http: Http) {
        }
      
        private getHeaders(){
          // I included these headers because otherwise FireFox
          // will request text/html instead of application/json
          let headers = new Headers();
          headers.append('Accept', 'application/json');
          return headers;
        }
        
        getmemberheader(): Promise&lt;string[]&gt; {
          return this.http
              .get(`/ReportService/MemberDatabaseCountryname`, {headers: this.getHeaders()})
              .toPromise()
              .then(this.extractData)
              .catch(this.handleError);
        }  
  
        private extractData(res: Response) {
          let body = res.json();
         
          return body || {};
        }
        private handleError(error: any): Promise&lt;any&gt; {
          console.error('An error occurred', error);
          return Promise.reject(error.message || error);
        }
      }
  </code></pre>