A tool for managing JavaScript projects with multiple packages.

About

While developing Babel I followed a monorepo approach where the entire project was split into individual packages but everything lived in the same repo. This was great. It allowed super easy modularisation which meant the core was easier to approach and meant others could use the useful parts of Babel in their own projects.

This tool was abstracted out of that and deals with bootstrapping packages by linking them together as well as publishing them to npm. You can see the Babel repo for an example of a large Lerna project.

Usage

$ npm install -g lerna
$ lerna bootstrap

This will create a dummy VERSION file as well as a packages folder.

Bootstrap

$ lerna bootstrap

1. Link together all packages that depend on each other.
2. npm install all other dependencies of each package.

Updated

$ lerna updated

1. Check which packages have changed since the last release, and log it.

Publishing

$ lerna publish

1. Publish each module in packages that has been updated since the last version to npm with the tag prerelease.
2. Once all packages have been published, remove the prerelease tags and add the tags latest and stable.

If you need to publish prerelease versions, set an env variable. NPM_DIST_TAG=next lerna publish. This will add the tag you specify instead of latest and stable.

How it works

Lerna projects operate on a single version line. The version is kept in the file VERSION at the root of your project. When you run lerna publish, if a module has been updated since the last time a release was made, it will be updated to the new version you're releasing. This means that you only publish a new version of a package when you need to.