lerna

What is lerna?

Lerna is a tool that optimizes the workflow around managing multi-package repositories with git and npm. It allows you to manage your project's dependencies, versioning, and publishing in a more organized manner, especially when dealing with a monorepo containing multiple packages.

What are lerna's main functionalities?

Bootstrap

Installs all of the dependencies for each package, links any cross-dependencies, and ensures that each package can find and use the correct versions of each other.

lerna bootstrap

Publish

Helps with versioning of the changes and publishing packages that have been updated to npm. It can automatically determine version bumps based on conventional commits, create git tags, and push releases to the repository.

lerna publish

Run

Runs an npm script in each package that contains that script. The '--scope' flag can be used to run the script only in specified packages.

lerna run --scope my-package test

Exec

Executes an arbitrary command in each of your packages. In this example, it removes the 'node_modules' directory from each package.

lerna exec -- rm -rf ./node_modules

List

Lists all of the public packages in the current Lerna repo.

lerna list

Changed

Lists public packages that have changed since the last tagged release.

lerna changed

Diff

Shows the diff since the last release for a single package or all packages.

lerna diff

Import

Imports an external repository into the 'packages' folder of your Lerna monorepo, preserving the commit history.

lerna import <path-to-external-repository>

Other packages similar to lerna

nx

Nx is a suite of powerful, extensible dev tools that help you develop, test, build, and scale Angular and React applications with fully integrated support for monorepo management. It provides a more integrated experience for building applications compared to Lerna, which is more focused on package management.

README

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.

We are in the process of updating the docs to 2.x right now. Although the commands are the same, the docs below are mainly for 1.x (which is the version you get with a default npm install).

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.