How do I decide whether @types/* goes into `dependencies` or `devDependencies`?

Question

I use TypeScript 2 in my project. I'd like to use some js library, but also typings for that library. I can install types with simple npm install @types/some-library. I'm not sure if I should --save or --save-dev them. It seems to me that even DefinetelyTyped GitHub readme kind of mentions both versions, but never explains them. I would think that @types should be in devDependencies, as types are needed for development and aren't used in runtime, but I saw many times @types in just dependencies. I'm confused.

How should I decide whether @types/* goes into dependencies or devDependencies? Are there actually some more or less official instructions?

Answer 1

Let's say you're developing a package "A" that have @types/some-module package in devDependencies. For some reason you're exporting the type from @types/some-module

import {SomeType} from 'some-module';
export default class APackageClass {
     constructor(private config: SomeType) {

     }
}

Right now Typescript consumers of package "A" are unable to guess what SomeType is, since devDependencies of package "A" are NOT installed.

In that particular case you NEED to place @types/* package with regular "dependencies". For other cases "devDependencies" are good enough.

Answer 2

Are you generating a bundle? If so, I'd suggest not spending too much time debating what goes where. devDependencies and dependencies are only meaningful if you're publishing a package that can be used by others and you don't want to spam them with useless dependencies.

Place it in devDependencies. Like you said "types are needed for development and aren't used in runtime".