Argument of type 'boolean | undefined' is not assignable to parameter of type 'boolean'

Question

I tried to insert an authentication system in the Angular app. (This one.

After finishing everything, I got for this code:

private userCurrentState = new BehaviorSubject<boolean>(this.tokenAuthService.isSignedin());

this error message:

Argument of type 'boolean | undefined' is not assignable to parameter of type 'boolean'.

TokenAuthService code

getJwtToken() {
    return localStorage.getItem('auth_token');
}

validateToken() {
    const token = this.getJwtToken();
    if(token) {
        const payload = this.payload(token);
        if(payload) {
            return Object.values(this.tokenIssuer).indexOf(payload.iss) > -1 ? true : false;
        }
    }
    else {
       return false;
    }
}

isSignedin() {
    return this.validateToken();
}

How can I fix?

Answer 1

OK, maybe the previous answers will do the work, but they didn't explain why your function validateToken's return value results in undefined.

validateToken(){
  const token = this.getJwtToken();
  if(token){
    const payload = this.payload(token);
    if(payload){
      return Object.values(this.tokenIssuer).indexOf(payload.iss) > -1 ? true : false;
    }
    // You will get undefined here if payload is a falsy value
    // and thus you are getting <boolean|undefined> as result type.
    // One option is to provide else when !payload
  } else {
    return false;
  }
}