The TypeScript docs recommend the opposite, preferring interfaces. Interfaces are also structurally typed in TypeScript though; the major differences are that interfaces can only be used to declare object types: https://microsoft.github.io/TypeScript-New-Handbook/everythi...
The fact that interfaces are limited to typing objects but type aliases can also be used for functions is an easy +1 to type aliases.
My view is that declaration merging is a bit of an anti pattern that could cause trouble if two different people write an interface with the same name but to represent different data... now they get merged incorrectly. A type alias forces more explicit behavior where composition must be done by creating a new type alias as the union of two or more other types
type Foo = Bar & Baz
Yeah, not sure I agree yet but I could be persuaded... I don't think type aliases prevent extension, they just force it to be explicitly declared.
And that’s an intersection you’re describing there, not a union. Interfaces are explicit about extension as well, they use the “extends” keyword.
The explicitness I was referencing is around the declaration merging. Its automatic so unless there's a conflict between two interfaces with the same name but with different properties, a dev wouldn't know that it was being done.
I agree with using what makes sense for the scenario. I prefer type aliases for functions and interfaces for classes and that seems to work out pretty well so far.
That actually helps me understand some F# code I wrote last weekend as well regarding construction of objects of a certain type...
I didn't know about the difference between nominal vs structural types but your explanataion makes sense. It's the subtle distinction between a type vs a type alias that you pointed out.
I personally use type aliases in typescript over interfaces, I think they're a more natural fit for JS than interfaces but that's a separate conversation :)
Language design is really interesting especially the choices designers make. I feel like they must all pull at least in part from each other and would be curious to explore any relationships but if its total coincidence that's pretty incredible too.