This Week I Learned

How to analyze an npm package's inclusion in a project.

Context

I had a situation recently where I was trying to update an npm package in a yarn-based project I'm working on. I ran into trouble when I noticed that running yarn upgrade [package name] was not updating to the version I was expecting. I hadn't encountered this problem before, so I was a little stumped on it for a while. I was eventually able to track down a transitive dependency in the project that was pretty out of date and was limiting what version my package could be upgraded to.

Introducing -- yarn why

I queried it with my teammates, and one of them suggested I run yarn why [package name] to see where it was coming from, here is a sample output:

Helpfully, the output of the command lists "Reasons this module exists", pointing to precisely where in your repo the package is imported, including when the dependency is a transitive dependency:

Notice that the reason for archiver's existence in this repo is because it is a dependency of webdriverio.

Yarn why will also list out if a package is referenced multiple times:

Useful for tracking down package versions across a monorepo.