Typescript interface default values

Question

I have the following interface in TypeScript:

interface IX {
    a: string,
    b: any,
    c: AnotherType
}

I declare a variable of that t

Answer 1

Can I tell the interface to default the properties I don't supply to null? What would let me do this

No. But by default they are undefined which is mostly just fine. You can use the following pattern, i.e have a type assertion at the point of creation:

let x: IX = {} as any;

x.a = 'xyz'
x.b = 123
x.c = new AnotherType()

I have this and other patterns documented here : https://basarat.gitbook.io/typescript/main-1/lazyobjectliteralinitialization