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

Answer 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.