Find type of an unknown objects

Question

There are times when you need to work with packages which aren't built with typescript in mind. For example, I'm working with two.js package in a react + typescript project with strict mode turned on. I'm finding it very difficult to type each variable properly as I have no clue what a lot of functions return.

If I use any or don't mention a type, I get annoying errors like variable implicitly has an 'any' type and it feels like I'm in constant battle with the compiler instead of focusing on my work.

A lot of other languages have some function/keyword which gives you the exact class/type an object is based on. But in javascript's typeof & instanceof are completely useless as you can only use them to check if an object is of a certain class. And typeof simply returns object for any custom object.

I love typescript but this is very annoying. How do I get around this? I've tried googling online but couldn't find a solid way to deal with this problem.

typeof should return you the type as a string though, just console.log it no? — laenNoCode, Dec 26 '21 at 16:24
i guess it's duplicate of https://stackoverflow.com/questions/13613524/get-an-objects-class-name-at-runtime the solution is to use ".constructor.name" — laenNoCode, Dec 26 '21 at 16:32
maybe just run it once. Some depending on if the library is a typescript library, vscode (or some other editors) might give you the documentation of it. Otherwise check the documentation if availible. That's how i do it — laenNoCode, Dec 26 '21 at 16:39

score 0 · Answer 1 · answered Dec 26 '21 at 17:14

If I use any or don't mention a type, I get annoying errors like variable implicitly has an 'any' type

The message explains that the variable in question has no explicit annotation. This won't happen if you explicitly annotate/assert any.

If you want to keep your program type-safe, your only options are to

create a declaration file for the imported module, or
use assertions when you use the untyped imports

There's not another way for TypeScript to know what the imported types are because TS is a static, structural type checker, and its purpose is to help keep your program type-safe.

Find type of an unknown objects

1 Answers1