Can a TypeScript interface be spread into another interface?

Question

In JavaScript, an object can be spread into another object using the spread syntax:

const a = {one: 1, two: 2}
const b = {...a, three: 3} // = {one: 1, two: 2, three: 3}

Is there a way to spread an typescript interface into another interface in such a way?

interface IA {
  one: number;
  two: number;
}

interface IB {
  ...IA; // Does not work like this
  three: number;
}

So that the resulting interface IB would look like this:

{
  one: number;
  two: number;
  three: number;
}

Answer 1

You can just use inheritance to do that :

interface IA {
    one: number;
    two: number;
}
interface IC {
    other: number;
    four: number;
}
interface IB extends IA, IC {
    three: number;
}