What is Lerna?

Lerna is a free tool that helps developers manage many related JavaScript projects that live together in one big folder, called a monorepo. It makes it easier to share code, keep versions in sync, and run tasks across all the projects at once.

Let's break it down

  • Lerna: the name of the tool; think of it as a helper for big code collections.
  • Tool: a piece of software you run on your computer.
  • Manage: organize, update, and keep things tidy.
  • Many related JavaScript projects: separate pieces of code (called packages) that work together, all written in the JavaScript language.
  • Monorepo: short for “multiple repository”; a single folder that holds all those packages instead of spreading them across many separate folders.
  • Share code: reuse the same functions or components in different packages.
  • Keep versions in sync: make sure every package says it’s at version 1.2.3 at the same time, so they work together smoothly.
  • Run tasks across all projects: do things like testing or building one time and have it affect every package.

Why does it matter?

If you’re building a product made of many small parts (like a UI library, a server API, and a CLI tool), Lerna saves you time and reduces mistakes by handling the plumbing for you. It lets teams collaborate without worrying about each piece getting out of step.

Where is it used?

  • Large open-source libraries such as Babel and React-router keep their core, plugins, and presets together with Lerna.
  • Companies like Airbnb and Shopify use Lerna to coordinate internal UI component libraries, backend services, and tooling in a single repository.
  • Teams building design systems (e.g., Material-UI) use Lerna to publish multiple packages (buttons, icons, themes) from one place.
  • Open-source testing frameworks like Jest have used Lerna to manage their core runner, plugins, and utilities.

Good things about it

  • Simplifies versioning: you can bump all package versions with one command.
  • Speeds up development: shared node_modules and parallel task execution reduce install and build times.
  • Keeps code consistent: common scripts and configurations live in one spot.
  • Easy publishing: Lerna can automatically publish updated packages to npm.
  • Works with existing tools: integrates with Yarn, npm, and modern bundlers.

Not-so-good things

  • Learning curve: new developers may need time to understand monorepo concepts and Lerna commands.
  • Can become heavy: very large monorepos may slow down Git operations or CI pipelines if not tuned.
  • Limited to JavaScript/TypeScript ecosystems; not a fit for mixed-language projects without extra setup.
  • Some features overlap with newer tools (e.g., Nx, Turborepo), so you might choose a different solution as the ecosystem evolves.