[jbmilgrom]

TypeScript is intentionally _structurally_ typed (except for enums). The example you describe would only be caught by a _nominally_ typed language (think Java).

Structural typing is great when programming functionally (i.e. with immutability) when the most important thing is the shape of inputs and outputs of functions, instead of named objects (like Person) and properties. In a functional program, for example, "printAge" would likely be called something like "print" or "printNumber" since that is what it is doing to its input _value_.

I think a lot of the misunderstanding I've seen recently around TypeScript (like from the Rails creator) comes from the misuse of TypeScript - if you use TypeScript in an object-oriented way, its going to be significantly less helpful.

[Draiken]

>if you use TypeScript in an object-oriented way

I don't follow this one. I've never seen anyone use TypeScript with an OO approach aside from, ironically, the .NET folks.

The code I wrote has nothing OO with it and we can already see the issues. The majority of TS I've ever worked with was written for React and it still would benefit greatly from nominal types as you call them (thanks I didn't know that terminology).

I don't see everyone misusing TS. For me, it's simply a very limited language as far as typed languages go. As a result, it's a shame that it's what is being touted as a good example of why you should use typed languages.

[cdaven]

First, Angular uses classes, and React supports class-based components.

Then, if you have converted lots of Javascript into Typescript, you have probably found several type-related bugs.

On one hand, this makes you (me) trust Typescript more, and feel safer knowing that your types are correct.

Later, you discover that a few of the declared types are wrong! You also still get "this" wrong in callbacks.

You could say that Typescript lets you try to get your types right, but you have to do the heavy lifting yourself.

[zogrodea]

That hasn’t been my experience. ReScript and Elm are much better compared to the fragile types I’ve encountered with Typescript (where I needed to write code to do the type checking). Happy if you’ve found something that works for you though.