Angular:: error TS2532: Object is possibly 'undefined'

Question

I was doing the angular Tour-hero project(replaced Hero with 'User'). There when I made the Hero(User) and Hero-detail(User-detail) separate and when I tried to access the details, it is not showing and the update function also doesn't work. It is showing this error:

error TS2532: Object is possibly 'undefined'.

6 <input id="user-name" [(ngModel)]="user.name" placeholder="name">

The user object is,I think, giving the problem. But when I tried to do it exactly like the tutorial with the addition of MessageService and all,it works. But when I removed all that,it is giving this error. Thanks in advance for the help.

user-detail.component.html:

<div>
  <h2>{{user.name | uppercase}} Details</h2>
  <div><span>id: </span>{{user.id}}</div>
  <div>
        <label for="user-name">User name: </label>
        <input id="user-name" [(ngModel)]="user.name" placeholder="name">
    </div>
    <button (click)="goBack()">Back</button>
    <button (click)="save()">Save</button>
</div>

user-detail.component.ts:

import { Component, OnInit } from '@angular/core';
import { User } from 'src/app/model/user';
import { UserService } from 'src/app/services/user/user.service';
import { Location } from '@angular/common';
import { ActivatedRoute } from '@angular/router';


@Component({
  selector: 'app-user-detail',
  templateUrl: './user-detail.component.html',
  styleUrls: ['./user-detail.component.scss']
})
export class UserDetailComponent implements OnInit {
  user?: User

  constructor(
    private userService: UserService,
    private location: Location,
    private route: ActivatedRoute
  ) { }

  ngOnInit(): void {
    this.getUser();
  }

  getUser(): void {
    const id =
     parseInt(this.route.snapshot.paramMap.get('id')!, 1);
    this.userService.getUser(id)
      .subscribe(user => this.user = user);
  }

  goBack(): void {
    this.location.back();
  }

  save():void {
    if(this.user){
      this.userService.updateUser(this.user)
        .subscribe(() => this.goBack())
    }
  }

}

user.service.ts:

import { Injectable } from '@angular/core';
import { User } from 'src/app/model/user';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { catchError } from 'rxjs/operators';

@Injectable({
  providedIn: 'root'
})
export class UserService {
  
  private usersUrl = 'api/users/';

  httpOptions = {
    headers: new HttpHeaders({ 'Content-Type': 'application/json'})
  };

  getUsers(): Observable<User[]> {
    return this.http.get<User[]>(this.usersUrl).pipe(
      catchError(this.handleError<User[]>('getUsers',[]))
    );
  }

  /** GET hero by id. Will 404 if id not found */
  getUser(id: number): Observable<User> {
    const url = `${this.usersUrl}/${id}`;
    return this.http.get<User>(url).pipe(
      catchError(this.handleError<User>(`getUser id=${id}`))
    );
  }

  updateUser(user: User): Observable<any> {
    return this.http.put(this.usersUrl, user, this.httpOptions)
    .pipe(
        catchError(this.handleError<User[]>('getUsers',[]))
    );
  }

  addUser(user: User): Observable<User>{
    return this.http.post<User>(this.usersUrl, user, this.httpOptions)
      .pipe(
        catchError(this.handleError<User>('addUser'))
      )
  }

  deleteUser(id: number): Observable<User>{
    const url = `${this.usersUrl}/${id}`;

    return this.http.delete<User>(url, this.httpOptions).pipe(
      catchError(this.handleError<User>('deleteUser'))
    )
  }

  constructor(private http: HttpClient) { }

  private handleError<T>(operation = 'operation', result?:T){
    return (error: any): Observable<T> => {
      console.error(error);
      return of(result as T);
    }
  }
}

Disease

Does this answer your question? How can I solve the error 'TS2532: Object is possibly 'undefined'?. How to suppress “error TS2533: Object is possibly 'null' or 'undefined'”? – Harrisonharrod

Answer 1

I Believe this error is occurred due to typescript version 2.1 or later, your code is perfect! There is no any issue, but the way of deceleration of variable without initialized may cause of this error,

Now If you the know the user value or you want to initialized with any default values then please initialized your user variable inside constructor like below

user: User;

constructor() {
  this.user = {
    id: 0,
    name: ''
  };
}

Another solution is to make use of 'Definite Assignment Assertion' to tell typescript that this variable will have a value at runtime, like below

component.ts

user!: User;

Also make change with component.html file like below

<div>
  <h2>{{user?.name! | uppercase}} Details</h2>
  <div><span>id: </span>{{user?.id!}}</div>
  <div>
    <label for="user-name">User name: </label>
    <input id="user-name" [(ngModel)]="user?.name!" placeholder="name">
  </div>
  <button (click)="goBack()">Back</button>
  <button (click)="save()">Save</button>
</div>

Offhand

One more thing, I want to ask. As you can see this is a list which contains user names. I want to make a login system, based on these user names. Like using theses names, one can login into a site. Any suggestion on how to do it? I don't want to do it as a full-stack app. I used fake web-api as backend. So where should I store these names and how I retrieve it? – Disease

you can use firebase @OusiBoi – Flocculus

I don't want to use firebase. I want to just make it using localStorage – Disease

Alright as without actual server, you want to make login system, then you need create some mock services which will read data offline for that you need to create a JSON file which will contain the list of users with login credentials inside your project directory, verify authentication from that JSON file, if authentication passed then route the user on dashboard or home screen, Start perform other operation with respect to your requirement, Please note this is not a actual solution, it's just a idea through which you can meet your expectation, – Offhand

Answer 2

You don't need to mark user as optional

user-detail.component.ts:

import { Component, OnInit } from '@angular/core';
import { User } from 'src/app/model/user';
import { UserService } from 'src/app/services/user/user.service';
import { Location } from '@angular/common';
import { ActivatedRoute } from '@angular/router';


@Component({
  selector: 'app-user-detail',
  templateUrl: './user-detail.component.html',
  styleUrls: ['./user-detail.component.scss']
})
export class UserDetailComponent implements OnInit {
  user: User

  constructor(
    private userService: UserService,
    private location: Location,
    private route: ActivatedRoute
  ) { }

  ngOnInit(): void {
    this.getUser();
  }

  getUser(): void {
    const id =
     parseInt(this.route.snapshot.paramMap.get('id')!, 1);
    this.userService.getUser(id)
      .subscribe(user => this.user = user);
  }

  goBack(): void {
    this.location.back();
  }

  save():void {
    if(this.user){
      this.userService.updateUser(this.user)
        .subscribe(() => this.goBack())
    }
  }

}

Flocculus

It gives this error ' error TS2564: Property 'user' has no initializer and is not definitely assigned in the constructor. 14 user: User ' – Disease

Answer 3

1. If the Error occurring in the HTML Template then it is because the object you have created is undefined.
2. You have to initialize to a default value, this error is occurred because the TypeScript version is changed in Angular.
3. Make Sure your Server is online or restart it.

*Answer : In the Html template where you access the object make a condition i.e. ngIf=(user)

<div class="container" *ngIf="user">
<h5>{{ user.name }}</h5>
<p>Server status is {{ user.status }}</p></div>

Lindsley