Introduction to Lerna

Lerna is a powerful tool for managing JavaScript projects with multiple packages. It helps in maintaining dependencies, running scripts, and versioning in a monorepo environment.

Installation

npm install --global lerna

Basic Setup

lerna init

This command initializes a new Lerna repository.

Creating Packages

lerna create package-name

Creates a new package inside the packages directory.

Linking Packages

lerna link

Links all packages together that are dependencies of each other.

Publishing Packages

lerna publish

Publishes all updated packages to the npm registry.

Running Commands

lerna run script-name

Runs a script in the package’s package.json in each package that contains the script.

Executing custom scripts

lerna exec -- <script>

Executes an arbitrary script in each package’s directory.

Adding Dependencies

lerna add package-name

Adds a dependency on a package from the monorepo to another package in the monorepo, using the `–scope` flag if needed.

Examples

Here’s an example of a simple application using Lerna:

  lerna init
  lerna create utils
  lerna create app
 
  # Add lodash to utils package
  lerna add lodash --scope=utils
  
  # Add utils package as dependency to app
  lerna add utils --scope=app
 
  # utils/index.js
  import _ from 'lodash';
  export const add = (a, b) => _.add(a, b);
  
  # app/index.js
  import { add } from 'utils';
  console.log(add(1, 2)); // prints 3

By using Lerna, we efficiently manage the dependencies and scripts across multiple packages in our project, making development easier and more organized.

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