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.