What could be the reason for receiving 'undefined' in TypeScript after saving data in a variable?

When working on my program, I encountered an issue where I am trying to create a service and declare a variable within the service. I then created a get() method in the service to print the variable by calling the service method from a component, but I keep getting undefined as the output. Why is this happening?

AppComponent.ts

import { Component } from '@angular/core';


@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})


export class AppComponent {


  }

}

AppComponent.html

<app-comp1></app-comp1>

Comp1Component.ts

import { Component, OnInit } from '@angular/core';
import { AService } from 'src/app/services/a.service';

@Component({
  selector: 'app-comp1',
  templateUrl: './comp1.component.html',
  styleUrls: ['./comp1.component.css']
})
export class Comp1Component implements OnInit {

  constructor(private aService:AService) { }

  ngOnInit() {
    this.aService.getFunc1();
  }

}

AService.ts

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class AService {

  private a;


  constructor() { }

  public func1():void
  {
    this.a=11;

  }


  public getFunc1()
  {
    console.log(this.a);
  }
}

Answer №1

By failing to call func1() in the code snippet provided, you are not assigning a value to the variable held in the service. The correct sequence would be to first call func1() before calling getFunc1(). This way, the correct order should look like:

ngOnInit() {
    this.aService.func1()
    this.aService.getFunc1()
} 

Answer №2

Ensure that the service is properly integrated into your module. (Alternatively, you can specify it as a provider in the component.)

@NgModule({

  ...
  providers: [AService,...],
  ...
})

Answer №3

If you are encountering the issue of receiving undefined on the service, the solution is to make the service Injectable within the app. You can achieve this by declaring the service as follows:

@Injectable({
  providedIn: 'root'
})

export class AService {
//service implementation
}

In case the service needs to be scoped at the module level, simply modify the providedIn: 'module'

To gain a deeper understanding of providers in Angular, refer to the official documentation: https://angular.io/guide/providers

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