Initializing array of objects - Angular

Question

I have an array of objects and when I try to access to it, I get an error saying:

TypeError: Cannot set property 'ID' of undefined

My code is the following:

export class Carimplements OnInit {
  pieces: Piece[] = [];

  test(pos){
    this.pieces[pos].ID = "test";
  }
}

being Piece an object

export class Piece{
    ID: string;
    doors: string;
}

I call to test(pos) from the HTML with a valid position.

I guess that I am trying to access to the position X of an array that has not been initialized. How could I do it? Is it possible to create a constructor?

Answer 1

• Correct syntax for defining array types in TypeScript is this:

  pieces: Piece[] = [];
  

• The error is a runtime error. When you run your app you have an empty array pieces (but the variable still initialized with []) but you call test(whatever) which tries to access an array element whatever that doesn't exist.

  You can do for example this:

  pieces: Piece[] = [{
    ID: '1',
    doors: 'foo'
  }];
  

  and then test this method with test(0).

Answer 2

let pieces: Piece[]  = [];

//initialize object before assigning value
test(pos){
    this.pieces[pos] = new Piece();
    this.pieces[pos].ID = "test";
  }