Error:property 'token' does not exist on type' () => any'

I have created a provider for authentication in ionic2 and Angualr2 for login, which is as follows:

login provider

@Injectable()
export class Service{
public token : any;
constructor(public http: Http, public storage: Storage){}

    login(credentials){
    return new Promise((resolve, reject)=>{
    //headers implemented.
    this.http.post('url', {headers: headers}, credentials)
    .subscribe(res=>{
    data = res.json();
    this.token = data.token // error is shown here. red line on token.
    storage.set('token',data.token)
    resolve(credentials);});

Error which is reflected on the token is mentioned in the comment line on the word token of data.token.

Need Help.

via Aditya Jain