Typescript get properties of Parent interface from Child interface

i have following example from code

interface A {
    a:string;
}

interface B extends A{
    b:string;
}

const b:B = {
    a:'a',
    b:'b'
}

const a:A = b;

console.log(a)

The question is. Now it prints both properties ‘a’ and ‘b’. However I would only like to get the A properties excluding the B properties.

Any anser appreciated.