Typescript automatically get interface properties in a class

This is now possible in Typescript using class/interface merging.

interface Foo {
    a: number;
}

interface Baz extends Foo { }
class Baz {
    constructor() {
        console.log(this.a); // no error here
    }
}

https://github.com/Microsoft/TypeScript/issues/340#issuecomment-184964440