Declaration of variables and properties, types in Typescript. What is the correct approach?

Question

typescript

Actually the situation is this:
There is a code:

export default class Cookies {
    public type: string;
    public model: string;
    public status: string;

    getStatus(t: string) : string {
        console.log(t + ' : ' + this.status);
    }
}

How would it be more correct to declare properties and methods in this class?
Through a separate file (module):

interface cooking {
    public type: string;
    public model: string;
    public status: string;

    getStatus(t: string) : string;
}

class Cookies implement cooking ...

Or by creating a *.d.ts file:

declare namespace cooking {
    export interface cooking {
        public type: string;
        public model: string;
        public status: string;

        getStatus(t: string) : string;
    }
}

And in general, is the use of *.d.ts files for describing types relevant, or should they be used only if external libraries not written in typescript are connected?

Answer 1

In this case, there is no need to describe anything separately - everything is described in the code. *.d.ts are needed only if either is written in JS, but it must be included from TS.