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Syncpack
This documentation is for v14 alpha, the docs for v13 stable are archived.

Peer Dependencies

If any of your packages define peerDependencies (find out with syncpack list --dependency-types peer) it's really important that we understand them as they have a very different role.

dependencies tend to be exact (1.2.3) or clamped within the patch ~1.2.0 or sometimes even minor ^1.2.0 ranges. They're narrower in scope because there we are a consumer and we want higher confidence over knowing what we are running.

peerDependencies tend to be far broader in scope because in those scenarios we are a provider and we want our package to be suitable for as many consuming projects as possible. These versions tend to span entire majors (^1) and sometimes multiple majors (>=6.0.0 <9.0.0).

Why this matters

Section titled “Why this matters”

Unless your project is well-organised using Version Groups, it is very likely that at some point you will see a version mismatch because a peer dependency is not equal to a production dependency.

Here's a common example:

  1. One of the packages you develop is an ESLint Plugin and in its peerDependencies you define a range of "eslint": ">=6.0.0 <9.0.0" for the ESLint versions it is compatible with.
  2. Elsewhere you have "eslint": "8.53.0" installed under devDependencies because you use ESLint to lint the monorepo.

Syncpack will report a version mismatch because ESLint is referenced twice with wildly different versions.

That we don't consider this particular mismatch to be a problem is domain knowledge about our specific project. Syncpack needs us to share with it that domain knowledge via its Configuration file.