Error: The argument provided for user.token is of type 'string | undefined' which cannot be assigned to a parameter of type 'string'

I'm currently engaged in a project that involves ASP.NET Core Web API and Angular 13.

Here is the login post request from the endpoint:

> https://localhost:44396/api/v1/auth/login

    {
       "status_code": 200,
       "message": "Successfully Logged In",
       "result": {
           "token": "gggggffffffffffffdddddddddddd",
           "user": {
               "id": 3,
               "user_name": "smith",
               "last_login": "2022-01-03T12:35:26.0305649"
              },
           "roles": [
               "Teacher"
           ],
           "expires": "2022-01-03T14:40:33Z"
       }
    }

Below is the Angular code snippet:

user.ts:

export interface IResponse<T> {
  message: string;
  error: boolean;
  code: number;
  results: T;
}

export interface IUser {
  userName?: string;
  lastLogin?: Date;
  token?: string;
  roles?: string[];
  expires?: Date;
}

auth.service.ts:

export class AuthService {
  baseUrl = environment.apiUrl;
  private currentUserSource = new ReplaySubject<IUser>(1);
  currentUser$ = this.currentUserSource.asObservable();

  constructor(private http: HttpClient, private router: Router) { }

  login(model: any){
    return this.http.post(this.baseUrl+'auth/login', model).pipe(
      map((res: IUser)=>{
        const user = res;
        if(user){
          this.setCurrentUser(user);
        }
      })
    )
  }

  setCurrentUser(user: IUser){
    if(user){
      user.roles = [];
      const roles = this.getDecodedToken(user.token).role;//copy token to jwt.io see .role
      Array.isArray(roles) ? user.roles = roles : user.roles.push(roles);
      localStorage.setItem('user', JSON.stringify(user));
      this.currentUserSource.next(user);
    }
  }

  getDecodedToken(token: string) {
    return JSON.parse(atob(token.split('.')[1]));
  }
}

An error was encountered with the following message:

error TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.

The problematic code line highlighted is within setCurrentUser: user.token

How can I resolve this issue?

Answer №1

Give it a shot

let userRoles = this.retrieveUserRoles(user.token || '').roles;

Answer №2

Consider replacing the "if (user) { " statement in your code with the following:

if (user && user.token) {

This adjustment should provide TypeScript with the necessary information that user.token does indeed exist, even though your interface indicates it is optional.

If this solution does not resolve the issue, you can try the alternative approach below:

if (user && user.token != null) {

Answer №3

If you want to customize the user interface:

export interface IUser {
  ...
  token: string;
}

If you are confident that a token will always be present with a user.

Alternatively, you can explicitly specify the string type:

// Change this:
this.getDecodedToken(user.token)
// to this:
this.getDecodedToken(user.token as string)

The best approach is to ensure presence, as mentioned in the other response:

if (user && user.token) {...}

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