TS2532: The entity could be considered as undefined

Attempting API calls and generating a class for the API response model, but struggling to retrieve response values. Here is my code:

In app component.ts, I have ons_list as my response object, but unable to access ons_list.success.

In home.component.ts

import { Component, OnInit } from '@angular/core';
import { getOnsService } from "../../service/getOns.service";
import { result } from "../../model/result";
import { gold } from "../../model/gold.model";

@Component({
  selector: 'app-home',
  templateUrl: './home.component.html',
  providers: [],
})
export class HomeComponent implements OnInit {
  ons_list?: gold;
  ngOnInit(): void {
    this.get_Ons()
  }

  constructor(private service: getOnsService) {
    service.getOns().subscribe((response: gold) => {
      this.ons_list = response;
    });
    console.log(this.ons_list);
  }
  get_Ons() {
    this.service.getOns().subscribe((response: gold) => {
      this.ons_list = response;
    });
    console.log(this.ons_list);
  }
}

getOns.service.ts

import { Injectable } from "@angular/core";
import { HttpHeaders, HttpClient, HttpErrorResponse } from "@angular/common/http";
import { result } from "../model/result";
import { Observable } from "rxjs";
import { gold } from "../model/gold.model";

@Injectable({
  providedIn: 'root'
})
export class getOnsService {
  getheaders() {
    return new HttpHeaders({
      "Content-Type": "application/json",
      'Authorization': 'apikey 71kRhLc4nPehMJ6iPerw4s:4qStHMIhye28Ih4HjrqqFg'
    });
  }
  header = this.getheaders();
  constructor(private http: HttpClient) { }
  root_url = "https://api.collectapi.com/economy/";
  getOns(): Observable<gold> {
    return this.http.get<gold>(this.root_url + "goldPrice", { headers: this.header });
  }
}

gold.model.ts

import { result } from "./result";

export class gold {
  success?: string;
  result?: result[];
}

result.model.ts

export class result {
  name?: string;
  buy?: number;
  sell?: string;
}

home.component.html

<div class="grid">
  <div class="col-3 ">
    <p-card header="ONS">

      <ul>
        <li>
          {{ons_list.success}}
        </li>
      </ul>

    </p-card>
  </div>

Error message:

https://i.sstatic.net/fjLKW.png

API service:

https://i.sstatic.net/TFkMI.png

Answer №1

Identify the Issue

The error message indicates that the success parameter may be of an undefined type, but there is no defined response for this scenario. Various solutions can address this problem.

export class gold {
  success?: string; // not mandatory: string | undefined
  result?: result[];
}

Potential Fix # 1

  • Make success a mandatory field
export class gold {
  success: string; // required field (must be a string)
  result?: result[];
}

Potential Fix # 2

  • Ensure that the success parameter is declared beforehand
<div v-if="ons_list.success">
  {{ ons_list.success }}
</div>

Potential Fix # 3

  • If it is undefined, set a default text
{{ ons_list.success ?? 'is undefined' }} <!-- should only be a string -->

or

{{ String(ons_list.success) }} <!-- should only be a string -->

Potential Fix # 4

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

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