TS: How to override properties with type intersection

Hi, let's imagine the situation. We have type

type A = {
  a: string;
  b: string;
}

We want to get a new type using an intersection. It's just what we thought

type AB = A & {
  b: number;
};

But it's not working☹️

Of course, we can use interfaces instread

interface A {
  a: string;
  b: string;
}

interface AB extends A {
  b: number;
}

But how do that with types? Let's create a new utility type that can help us

type Override<T1, T2> = Omit<T1, keyof T2> & T2;

type AB = Override<A, { b: number }>

Pretty easy and very helpful. 🤟

Comments

[marcosfreitas]

I think it could be more useful if We can still validates the presence of the properties as in the T1 interface.

interface T1 {
a: object
}

type overridenTypeOnly = Override

The result would be that "a" property has its type changed, but can't accept "b" property because it isn't in T1 interface.

Any solution for this?

[Andrew Nosov]

Awesome! Thanks you.

[Daniel M]

Thank you. That what I was looking for.

[mattvalleycodes]

Nice one, Viacheslav! Thanks for sharing.

[tanth1993]

many thanks

[Ujwal Setlur]

Very nice, thanks!

[Laurodm]

Thanks!