I’m mainly a backend programmer, so I know just a little typescript, but I don’t really understand what they’re asking for here. It sounds like they want to serialize and deserialize typescript types automatically? If so, that sounds like a good fit for a library, not something most languages offer. (Please educate me if I’m missing the point)
The problem is that the deserialization is untyped. It's just a Javascript object. Usually, the first thing you'll do is to cast it to a typed Typescript definition, but there's no way to guarantee that it actually fits that definition. No type information exists at runtime. It's used solely to check the code itself during compilation.
So any time you get data from outside of your program (over the network, from a database, out of a config file, etc.) you just have to hope that it actually fits the type. You can write code to check it... but you have to write that code yourself.
There are libraries you can use. For example, you can use a Data Description Language with a simpler type system, which usually suffices for the kind of data you want to serialize. Then you can use that to generate both a Typescript definition and a runtime type checker. But that's inelegant, and not standard, so every project is different despite it being something everybody needs.