Array updated from the event callback

I am facing an issue where I need to update a specific array within my HTML template from a callback function triggered by an event. However, when trying to access the array inside the callback, it shows undefined.

export class HomePage {

  constructor(public navCtrl: NavController) {
    let consumer: string[]; // <=== The array that needs updating
    const realtime = new Ably.Realtime('API-KEY');
    const channel = realtime.channels.get("test");
    channel.subscribe((msg) => {

      console.log("Received: " + msg.data);
      consumer.push(msg.data); // <=== Unfortunately, "consumer" is undefined at this point

    });
  }

}

HTML TEMPLATE

  <div>
    <ul *ngFor="let item of consumer">
      <li>{{item}}</li>
    </ul>
  </div>

Answer №1

Reposition

let consumer: string[]; // <=== Modifying
this array outside of the constructor – maybe above it.

After that, delete the 'let' keyword and set it to an empty array = []; You are now able to utilize it in a template.

Answer №2

Make sure to properly set up your consumer array.

Update the following line

let consumer: string[];

to

let consumer: string[] = [];

This will initialize an empty array for you to add data to.

Best regards

Answer №3

There are two key issues to address:

  1. The component does not expose the `consumer` property, as it is currently only accessible within the constructor. This means you cannot iterate over it in the template. To resolve this, change it to a public property.

  2. The `consumer` property is never initialized. While its type is specified, no value is assigned to it. It remains empty without any data.

To rectify these issues, ensure that you declare and initialize the `consumer` property within your code:

export class HomePage {
  consumer: string[] = []; // Declare and assign initial values here
  constructor(public navCtrl: NavController) {
    const realtime = new Ably.Realtime('API-KEY');
    const channel = realtime.channels.get("test");
    channel.subscribe((msg) => {

      console.log("Received: " + msg.data);
      this.consumer.push(msg.data);

    });
  }

}

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