Specifying type of inline object in TypeScript

I’m using TypeScript and I have the following scenario.

Let’s say I have a base type and some derived types, something like this:

export interface Base {
  id: string;
}

export interface A extends Base {
  propA: string;
}

export interface B extends Base {
  propB: string;
}

And let’s say I also have an array of the base type:

let items: Base[];

Now, here’s my problem: I want to initialize that array with some objects, and I though I could just do this:

items = [
  {id: "1", propA: "foo"},
  {id: "2", propB: "bar"}
];

However, this doesn’t work, I get an error from the compiler saying that:

TS2322: Type ‘{ id: string; propA: string; }’ is not assignable to
type ‘Base’.   Object literal may only specify known properties, and
‘propA’ does not exist in type ‘Base’.

But the objects I declared are indeed instances of Base, and in fact if I do something like:

const objA: A = {id: "1", propA: "foo"};
items.push(objA);

the compiler doesn’t complain.

So, is it possible to do this inline object declaration, or am I forced to declare all objects separately and manually pushing them onto the array?

>Solution :

You can do either

items = [
    { id: "1", propA: "foo" } as A,
    { id: "2", propB: "bar" } as B
];

or

let items: Array<A | B>;