How to migrate from lerna to pnpm

Migrating from Lerna to pnpm involves restructuring project management, optimizing dependency management, and improving workflow efficiency. The following is a detailed and well-organized migration process, illustrated with a specific example.

Step 1: Assess the Existing Lerna Project Structure

Before initiating the migration, conduct a comprehensive assessment of the current Lerna-based project. This includes understanding dependencies between all packages, the build workflow, and the release process.

Example: Assume we have a monorepo managed by Lerna containing three packages: package-a, package-b, and package-c. Both package-a and package-b depend on package-c.

Step 2: Install and Configure pnpm

After confirming the project structure and dependencies, install pnpm. pnpm can be installed using npm:

bash
npm install -g pnpm

Next, to use pnpm within the monorepo, create a pnpm-workspace.yaml file to define workspace settings.

Example: Create pnpm-workspace.yaml in the project root with the following content:

yaml
packages:
  - 'packages/*'

Step 3: Migrate Dependency Management for Each Package

Migrate dependency management from Lerna to pnpm for each package's package.json. This involves using pnpm commands to install dependencies and ensuring all internal dependencies are correctly configured using pnpm's workspace linking.

Example: For package-a, if it depends on package-c, specify the dependency in package-a's package.json using pnpm syntax:

json
"dependencies": {
  "package-c": "workspace:^1.0.0"
}

Step 4: Adjust CI/CD Scripts

During migration, update CI/CD scripts to use pnpm commands and configurations. This may involve modifying build scripts, test scripts, and deployment scripts.

Example: In the CI configuration file, replace npm or yarn commands with pnpm commands:

yaml
build:
  script:
    - pnpm install
    - pnpm run build

Step 5: Validate and Test the Migration

After completing the above steps, conduct comprehensive testing to ensure all packages can correctly install dependencies, build, and run. This may include unit tests, integration tests, and end-to-end tests.

Example: Run pnpm commands to verify successful installation and build:

bash
pnpm install
pnpm run build

Step 6: Cleanup and Optimization After Migration

After migration, perform cleanup tasks such as removing unnecessary Lerna configuration files and optimizing new pnpm configurations.

By following these steps, you can successfully migrate from Lerna to pnpm, enhancing dependency management efficiency and optimizing the entire project's build and release process. This example should help you understand the specific steps and considerations involved in the migration.

Lerna is a tool for managing JavaScript projects with multiple packages, optimizing workflows that are difficult to handle with Git and npm. However, Lerna does not directly handle package dependencies and requires pairing with package managers like npm or yarn.

pnpm is a space-saving package manager that saves disk space through hard links and symbolic links and provides native support for monorepo projects. This means we can achieve the same effect as Lerna paired with npm or yarn by using pnpm alone.

Migrating from Lerna to pnpm can be broken down into the following steps:

1. Evaluate project requirements

First, evaluate the existing Lerna project structure and dependencies to determine if all functionalities can be equivalently implemented in pnpm. This includes:

• Package version synchronization
• Handling inter-package dependencies
• Release process
• Custom scripts

2. Install pnpm

Next, install pnpm in your development environment using the following command:

sh
npm install -g pnpm

3. Initialize pnpm workspace

Create a pnpm-workspace.yaml file to define the workspace settings using the following command:

sh
pnpm init

Then edit this file to include a configuration similar to the following, specifying the package locations:

yaml
packages:
  - 'packages/*'

4. Adjust package.json file

In the root directory's package.json file, add pnpm workspace configuration:

json
{
  "private": true,
  "workspaces": [
    "packages/*"
  ]
}

5. Remove Lerna configuration

Remove the Lerna configuration file lerna.json and ensure that related Lerna commands are removed from the package.json scripts section.

6. Migrate scripts and commands

If there are scripts using Lerna for package management (e.g., lerna bootstrap), modify them to use pnpm equivalents. For example, lerna bootstrap can be replaced with pnpm install since pnpm automatically links packages within the workspace.

7. Test

After completing the configuration, thoroughly test the entire project to ensure all dependencies are correctly installed, scripts run as expected, and CI/CD pipelines are unaffected.

8. Update documentation and CI/CD configuration

Ensure to update project documentation to reflect new build steps and commands, and verify that CI/CD systems use pnpm for dependency installation and task execution.

Example

Suppose we have a project managed by Lerna with two packages: package-a and package-b, where package-b depends on package-a.

In Lerna, we might have a lerna.json file in the root directory with the following content:

json
{
  "packages": ["packages/*"],
  "version": "independent"
}

We would also see similar "scripts" in the package.json file:

json
{
  "scripts": {
    "bootstrap": "lerna bootstrap",
    "publish": "lerna publish"
  }
}

After migrating to pnpm, we no longer need the lerna.json file. Instead, add workspace configuration to the root package.json and update the scripts:

json
{
  "private": true,
  "workspaces": ["packages/*"],
  "scripts": {
    "install": "pnpm install",
    "publish": "pnpm publish --filter ./packages/*"
  }
}

This completes the basic migration process from Lerna to pnpm. Of course, specific project migrations may be more complex and require step-by-step execution to ensure each step is correctly implemented.