如何在 TypeScript 中使用区分不同的 object 类型？

Question

How to distinguish different object type in TypeScript?

interface CC {
    a: number;
    b: string
}

interface B {
    c:number
}



const obj:  CC |  B = {
    a: 1,
    c: 1
} 
// valid

I want the obj only valid when

{
  a:number,
  b:string
}

or

{
  c:number
}

not what union type or intersection type behave.

Answer 1

One way to force typescript to pick either B or CC is to set a common variable with a specific value.

Example :

type CC = {
    type: 1;
    a: number;
    b: string
};

type B = {
    type: 2;
    c: number
};

const obj: CC | B = {
    type: 1,
    a: 1,
    c: 1
};