Typescript duck typing

One of the main surprising feature of TypeScript in my opinion is ths so called "duck typing" that works great for interfaces in Typescript. "duck typing" is a concept for dynamic typing that has been integrated in Ruby and means:

"When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck." (by James Whitcomb Rileys)

 How does it work for interface? An Example:

Lets have the following object declarations:

let myObj = {

     lastname: "Petersen",
     surname: "Peter"
}

let myObj2 = {

     fullname: "Petersen",
     titel: "Dr."

and a simple interface declaration:

interface Name {

     lastname: string,
     surname: string
}

then the following expression is vaild in TypeScript:

let name: Name = myObj; 

but NOT this expression:

let name2: Name = myObj2;

Ok, this may be not be surprising at a second glance, but for a developer that has been shaped and stigmatized by Java for many years it is a surprisingly simple but effective feature.