Why my push-method is not working using Ionic?

Question

I am working with ionic 3 and I have problems with an alert controller when I try to push an element in mi array. I do not what is wrong with my code, I think that I only need to receive the parameters and push it to complete the action but I only get a big error when I try to execute my code.

I'm so sorry, I know that my English is so bad.

CODE

  addPregunta() {
    const prompt = this.alertCtrl.create({
      title: "Login",
      message: "Enter a name for this new album you're so keen on adding",
      inputs: [
        {
          name: "title",
          placeholder: "Title"
        }
      ],
      buttons: [
        {
          text: "Cancel",
          handler: data => {
            console.log("Cancel clicked");
          }
        },
        {
          text: "Save",
          handler: data => {
            const preObj = {
              type: "radio",
              label: data.title
            };
            this.preguntas.push(preObj);
            this.changeData(data.title);
            this.mermaidStart();
          }
        }
      ]
    });
    prompt.present();
  }

ARRAY

preguntas: object[];

ERROR

You are showing "ARRAY" preguntas: object[]; separately, without any context. It has to be defined in a scope in which the "CODE" can see it — so where exactly is it defined? — Stephen P
– Stephen P, Commented Feb 10, 2020 at 23:53
@C_Ogoo is preguntas: any[], sorry I had a mistake but the error is the same. And it is defined into the component at the top like another variable in angular/ionic. — ASASCED
– ASASCED, Commented Feb 10, 2020 at 23:56
@ASASCED, define your variable "preguntas" as preguntas:any[]=[] so preguntas is an empty array. if you define preguntas:any[], preguntas is null — Eliseo
– Eliseo, Commented Feb 11, 2020 at 7:32

C.OG · Accepted Answer · 2020-02-11 08:06:52Z

1

preguntas: object[]; The preguntas property is defined but it's not initialised with a value.

console.log(this.preguntas) // will be undefined

The problem is in the save handler:

{
  text: "Save",
  handler: data => {
    const preObj = {
      type: "radio",
      label: data.title
    };
    this.preguntas.push(preObj); // <-- the problem is with this line
    this.changeData(data.title);
    this.mermaidStart();
}

When this.preguntas.push(preObj) is called for the first time. this.preguntas is undefined, array.push will not work because this.preguntas is not an array.

The options you have are to initialise the preguntas property as an array, or check the value in the handler before your call .push.

Option 1

Initialise the property as an array

preguntas: object[] = [];

Option 2 Check the value in the save handler before pushing.

There are countless ways to check or even use an immutable approach

// similar style with your existing code
if(this.preguntas) {
  this.preguntas.push(preObj);
} else {
  this.preguntas = [preObj];
}

// immutable approach
this.preguntas = [...this.preguntas, preObj]

answered Feb 11, 2020 at 8:06

C.OG

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ASASCED Over a year ago

Thank you so much, its a simple error but yesterday I dindn't know what happend? :(

General Grievance · Accepted Answer · 2022-05-16 14:36:16Z

1

You have declared the variable as an Array type but you did not initialize it so fails when you are trying to push into it.

edited May 16, 2022 at 14:36

General Grievance

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answered Feb 11, 2020 at 0:13

German Cosano

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