Demo Project - Monorepo and Lerna

This is an hands-on project to help familiarize with Monorepos and Lerna. The repository consist in two libraries:

• @monorepo/core (v1.0.3): a fake server that returns the current date, if a client is connected to it;
• @monorepo/client (v3.8.18): a silly client that will connect to the core and ask for the current date, printing it in the console.

The concept behind this project is interact with versioning and multiple libraries, with two possible approaches:

1. common version: every library follows the same versioning;
2. individual version: each library implements its own version.

All the examples will take advantage of the adoption of conventional commits in order to:

• understand the next version the libraries will bump;
• create a proper changelog.

Before to start

First of all, you need to:

1. Clone the project

   git clone https://github.com/federicoibba/lerna-demo-project.git

2. Install the dependencies

   npm i

Setup Lerna

To install Lerna in the project, you just need to run:

npx lerna init

This command will:

• install the needed dependencies
• create a lerna.json file used as configuration file.

Edit the lerna.json in order to have the following structure:

{
  "$schema": "node_modules/lerna/schemas/lerna-schema.json",
  "version": "0.0.0",
  "command": {
    "version": {
      "conventionalCommits": true
    }
  }
}

Then, commit the changes with, for instance:

git add . && git commit -m "build: setup lerna"

Let's pretend that we need a do an urgent fix in @monorepo/core, because the epoch was needed, not a string date. Go to /core/index.js and change row 20, returning instead new Date().getTime(), then commit using a fix commit message:

git add core/index.js && git commit -m "fix: current date"

Use cases

Case 1. Common version

At this point, you may want to release the new library version. We will use two options that, for this demo project, prevent some errors and will help us focus on the versioning. Run hence:

npx lerna version --no-git-tag-version --no-push

Lerna will ask eventually if you are sure that the changes are correct, printing the future versions:

Changes:
 - @monorepo/client: 3.8.18 => 3.8.19
 - @monorepo/core: 1.0.3 => 3.8.19

In this case, which is the default behavior called Fixed/Locked, Lerna will see that the versions are highly different, conciliating the versions.

Case 2. Independent version

Let's say that the requirement is to keep the versioning different, then it's enough to just edit the lerna.json file and change the version row with independent instead of 0.0.0.

Also this time, run:

npx lerna version --no-git-tag-version --no-push

Lerna will propose a different bump strategy based on the independent key previously set, showing the following prompt:

Changes:
 - @monorepo/client: 3.8.18 => 3.8.19
 - @monorepo/core: 1.0.3 => 1.0.4

Read more

If you want to deep dive more on how the versioning works in Lerna, (follow this link)(https://lerna.js.org/docs/features/version-and-publish#fixedlocked-mode-default).