Issue with accessing class property in events.subscribe in Ionic3

Question

Issue with accessing class property in events.subscribe in Ionic3

I am currently working on a class that listens for events. When the event is triggered, I need to add the data that accompanies it to an array and then display it. Here's what my class looks like:

export class customClass {

  dataArray:Array<string>;

  constructor(public navCtrl: NavController, 
              public navParams: NavParams,
              public events: Events) {

    events.subscribe('event',
      (data) => {
        //some random code
        this.dataArray.push(data); //this fails
      }
    )
  }

The error message I keep receiving is: TypeError: undefined is not an object (evaluating '_this.communication.push')

I have searched extensively but cannot seem to find a solution to this issue.

angular typescript events ionic2 ionic3

Answer 1

Answer №1

element, I encountered an issue that required me to initialize a property with an empty array. Interestingly, I found that this simple step resolved the problem:

communication:Array<string> = [];

Answer 2

element, I encountered an issue that required me to initialize a property with an empty array. Interestingly, I found that this simple step resolved the problem:

communication:Array<string> = [];

Answer 3

Answer №2

The issue I encountered required me to start off the property with an empty array (Could someone provide insight on why this is necessary?)

Here's what happens when you try to do this:

someArray: Array<string>;

You're simply defining a property named someArray and specifying that its type is an Array of strings, but you're not initializing that property. Therefore, initially, someArray will be undefined.

So, when you attempt to execute this code:

this.someArray.push(data);

because this.someArray is undefined, you are essentially trying to invoke the push method on undefined, which results in an error (hence the message such as TypeError: undefined is not an object).

As mentioned earlier, the solution involves initializing someArray with an empty Array. This way, you can successfully use the push method since it is defined in every object whose type is an Array.

someArray: Array<string> = [];

Answer 4

The issue I encountered required me to start off the property with an empty array (Could someone provide insight on why this is necessary?)

Here's what happens when you try to do this:

someArray: Array<string>;

You're simply defining a property named someArray and specifying that its type is an Array of strings, but you're not initializing that property. Therefore, initially, someArray will be undefined.

So, when you attempt to execute this code:

this.someArray.push(data);

because this.someArray is undefined, you are essentially trying to invoke the push method on undefined, which results in an error (hence the message such as TypeError: undefined is not an object).

As mentioned earlier, the solution involves initializing someArray with an empty Array. This way, you can successfully use the push method since it is defined in every object whose type is an Array.

someArray: Array<string> = [];

Answer 5

Answer №3

During the transpilation process of this code to JavaScript, an issue arises where the variable someArray ends up with a value of undefined. This is a common behavior of transpilers - you cannot push data into a variable that has not been properly initialized as an array. By explicitly defining

someArray:Array<string> = []

, it will transpile correctly into var someArray = [], allowing you to then push data into the array without any issues.

Answer 6

During the transpilation process of this code to JavaScript, an issue arises where the variable someArray ends up with a value of undefined. This is a common behavior of transpilers - you cannot push data into a variable that has not been properly initialized as an array. By explicitly defining

someArray:Array<string> = []

, it will transpile correctly into var someArray = [], allowing you to then push data into the array without any issues.

Issue with accessing class property in events.subscribe in Ionic3

Answer №1

Answer №2

Answer №3

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