Mastering Angular: Accessing undefined properties (specifically 'push')

Currently, I am in the process of learning Angular and have encountered an issue while working on an assignment. The error message that I am facing is "Cannot read properties of undefined (reading 'push')." Despite knowing that this is a common error, I am struggling to identify what I am doing wrong. I am hopeful that someone here can offer me some assistance.

In my assignment, I am attempting to separate even numbers into the "even" array and odd numbers into the "unEven" array. The problem arises when trying to push these numbers into their respective arrays. I have already declared and initialized them as empty arrays. However, I am uncertain about what else I can do to resolve this issue...

Below is a snippet from my .ts file:

import { Component, Input, OnInit, Output } from '@angular/core';

@Component({
  selector: 'app-game-control',
  templateUrl: './game-control.component.html',
  styleUrl: './game-control.component.css'
})
export class GameControlComponent implements OnInit{
  counter = 0;
  intervalID;
  even: number[]=[];
  unEven: number[]=[];

  onStartGame(){
    this.intervalID = setInterval(this.GameStarted,1000)
  }

  onStopGame(){
    clearInterval(this.intervalID)
  }

  GameStarted(){
    this.counter = this.counter +1;
    Number.isInteger(this.counter/2)? this.even.push(this.counter) : this.unEven.push(this.counter);
    console.log('Even numbers logged: '+ this.even);
    console.log('Odd numbers logged: '+ this.unEven);
  }
  ngOnInit(){}
}

Answer №1

It is important to pay attention to the value of this in your GameStarted method when using

setInterval(this.GameStarted,1000)
. This can result in a change of reference for this. To maintain the correct value of this, consider invoking the method with arrow functions or utilizing this.GameStarted.bind(this) in setInterval.

onStartGame(){
    this.intervalID = setInterval(this.GameStarted.bind(this), 1000)
    }

Answer №2

Give this revised approach a shot:

initializeGame(){
  this.intervalID = setInterval(() => this.gameCommenced(), 1000);
}

gameCommenced(){
  this.counter = this.counter + 1;
  Number.isInteger(this.counter / 2) ? this.even.push(this.counter) : this.unEven.push(this.counter);
  console.log('List of even numbers so far: ' + this.even);
  console.log('List of odd numbers so far: ' + this.unEven);
}

On top of that, it's advisable to adhere to the naming conventions in TypeScript/JavaScript. In general, method names should start with a lowercase letter. Thus, renaming GameStarted to gameStarted would be recommended.

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