Why peerDependencies over just dependencies?

[chrisdhanaraj]

So when I look through the package.json of your OSS projects and others (in this case, glamorous), I notice that many will add certain packages they depend on as peerDependencies instead of just dependencies. I'm curious to what the benefit is of this - at first glance, it just makes the user go through one more install step. Thanks!

[kentcdodds]

Hi @chrisdhanaraj,
You're correct! The user does have to go through one more install step. But you could also think of it as: "The user gets to go through one more install step." Specifically, that the user gets to choose which version of the peerDependency they want to use. Especially for React-based projects, it's better for them to list React as a peerDependency because you don't want each of your component libraries to bring all of React with them. It's like making a batch of cookies. You already have the flour, and you don't want the sugar to bring flour with it too. The flour is a peer-dependency of the sugar.

For glamorous specifically, I didn't want to bundle glamor with it because I see them as complimentary. I want people to use glamor directly in their app when it makes sense, and glamorous in other places. They interop so well together, and serve different use cases.

I hope that's helpful!