Learn TypeScript 3 by Building Web Applications

Structural typing

In TypeScript, usually, if things quack like ducks, then TypeScript assumes that they're ducks. Duck typing as it is called is baked into the language. We can say that TypeScript considers the compatibility of types. We’ll leverage this great feature in the projects to make things clear.

To give you an idea, if some function expects to receive an object of a Foo type and is instead called with an object of a Bar type, then TypeScript will not complain as long as Bar has the same structure as Foo. That is to say, a Bar object can be considered to be Foo if it exposes at least the expected properties/methods.

This is an oversimplification as there are actually many rules at play, depending on the considered types.

Structural ...