Installing an npm module as a devDependency of itself

Question

Let's say I've made a TDD tool called foo, and I want to use foo v1 to help me develop foo v2.

But when I npm install --save-dev foo@^1.0.0, npm says "Refusing to install foo as a dependency of itself".

1. Why does npm refuse to do this?
2. What can I do instead?

Workarounds I've got so far (and why they're not good enough):

• Workaround 1: just require the relevant script directly using a relative require, e.g. require('../lib') (this is how mocha does it, and it's how I've been doing it so far).

  • but if you're working on a new version of your module, adding features, perhaps even removing old features, then you're constantly having to alter not just the content of your tests but also their format, because you're actually using the thing you're working on to test the thing you're working on. If it breaks, you have to fix it in the dark with no tests to guide you. It would be much better to use the settled v1 API for tdd-ing the new v2 API.

• Workaround 2: publish a duplicate of your module to npm under a different name, like "foo-clone". (Then you can just install foo-clone as a devDependency of foo.)

  • but that seems messy and a misuse of npm. Anyway, if installing an exact clone would work, then what would be the harm in npm allowing me to install [an old version of] foo as a devDependency of foo?

Answer 1

Here is a better alternative to your Workaround 2.

---

Let's assume that you'll only need this dependency on early stage of development. So, before publishing first production-ready version you'll get rid of it, e.g. by adopting mocha solution (using current stable version to test itself).

In this case, instead of publishing duplicate package you could temporary rename your package (i.e. postfix it with -dev).

To guarantee that this renamed package will not be published, you could also add private flag.

So, your dev package.json will look something like:

{
  "name": "mytdd-dev",
  "version": "2.0.0-dev",
  "private": true,
  ...
  "devDependencies": {
    "mytdd": "1.x.x",
    ...
  },
  ...
}

Then, when your package will be ready for the first release, you'll remove all -dev postfixes, private flag and dev dependency on previous version.

The only problem with this solution is that you won't be able to publish early dev versions of your TDD tool to npm (as long as you'll depend on previous version).

---

if installing an exact clone would work, then what would be the harm in npm allowing me to install [an old version of] foo as a devDependency of foo

I think it's a safety precautions against circular dependencies.

If you believe that npm should make an exception for devDependencies here, which sounds reasonable to me, then you should post your suggestion to npm issues tracker.