Ionic 2 - TypeScript | Filling up an array with interface objects

Even after putting in the effort to research before posting this question, I'm aware that some might consider it trivial. However, as a newcomer to Typescript, I am facing considerable challenges with it.

Let me start by showing you my interface:

export interface Product {
  name?: string;
  image_url?: string;
  description?: string;
  price?: number;
  quantity?: number;
}

My goal is to create an array of type Product and populate it with random values.

To give you a clearer picture, here's how I'm attempting to achieve it:

export class HomePage {
  products: Product[];
  constructor(public navCtrl: NavController) {
    for (var i=0; i< 10; i++) {
      var random: number =  Math.floor(Math.random() * 10) + 1;
      this.products[i] = <Product>{
        name: `Test_${i}`,
        image_url: "https://unsplash.it/200/?random",
        description: "This is a short description",
        price: random,
        quantity: i
      };
    }
    console.log(this.products);
  }
}

However, upon running this code, I encounter the following error:

polyfills.js:3 Error: Uncaught (in promise): Error: Error in ./HomePage class HomePage_Host - inline template:0:0 caused by: Cannot set property '0' of undefined(…)

I would greatly appreciate if you could provide guidance on where I am going wrong or suggest ways to rectify the issue.

Thank you very much.

Answer №1

When using TypeScript to define a class member, it's important to remember to initialize the member:

class A {
    member: string[];
}

In the compiled JavaScript code, the member is not automatically created:

var A = (function () {
    function A() {
    }
    return A;
}());

To avoid errors, make sure to initialize the member like this:

export class HomePage {
  products: Product[];

  constructor(public navCtrl: NavController) {
    this.products = [];
    ...

If you fail to do so, the member will be undefined, leading to the error mentioned in your post.

Alternatively, you can initialize the member when declaring it:

export class HomePage {
  products: Product[] = [];

This approach will generate the same JavaScript code as before.

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