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

Issue

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?

Solution

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.

Answered By - wookieb