Typescript interface optional properties depending on other property

Question

Let\'s say we have the following Typescript interface:

interface Sample {
    key1: boolean;
    key2?: string;
    key3?: number;
};
         


        

Answer 1

Thought I'd mention another nice approach here could be to use a discriminated union:

enum ShapeKind {
    Circle,
    Square,
}

interface Circle {
    kind: ShapeKind.Circle;
    radius: number;
}

interface Square {
    kind: ShapeKind.Square;
    sideLength: number;
}

let c: Circle = {
    kind: ShapeKind.Square,
    //    ~~~~~~~~~~~~~~~~ Error!
    radius: 100,
}

As described in the Typescript docs: https://www.typescriptlang.org/docs/handbook/enums.html#union-enums-and-enum-member-types