Subset of object

[remote marten]

How can I effectively take only few arguments from parent object?

interface A {
    id: number;
    title: string;
    description: string;
}

interface B extends Omit<A , 'id'> {}

const a: A = {
    title: "",
    description: "",
    id: 0,
}

const b: B = {...a}; // attribute 'id' is also included in object 'b' even it's not in interface B.

I don't want to pick attributes manually.
And the second question, why assigning for object b is valid though id is not in interface B and b contains this attr in the end? I expected that only title and description will be present in this object. Thanks

[elfin granite]

And the second question, why assigning for object b is valid though id is not in interface B and b contains this attr in the end?
that is by design

TypeScript uses a structural type system

meaning you describe the general shape an object has to have to be of this kind

"If it walks like a duck and it quacks like a duck, then it must be a duck"

and since Bs only require a title and a description, all As are Bs

@remote marten

How can I effectively take only few arguments from parent object?
I don't want to pick attributes manually.
good question

you could do it manually by using object destructuring

like so

[feral tundra]

Ascor8522#7606

Playground Link

Preview:```ts
interface A {
id: number
title: string
description: string
}

interface B extends Omit<A, "id"> {}

const a: A = {
title: "",
description: "",
id: 0,
}

const {id, ...b} = a```

You can choose specific lines to embed by selecting them before copying the link.

[elfin granite]

!ts id b

[feral tundra]

(property) A.id: number /* 2:5, 12:5 */
const id: number /* 15:9 */``````ts
const b: {
    title: string;
    description: string;
} /* 15:16 */```

[elfin granite]

maybe having a function and a list of all the keys would help

you could then loop over the obejct and chose what keys to copy

[remote marten]

so there isn't any way that TS will do it for me just by defined interface right

[elfin granite]

no

interfaces and types don't exist at runtime

they are simply removed, and don't change the code you write

the JS you write is the JS that is executed

the TS types are only there to help the compiler check your code