MonoRepo Example with Lerna and Yarn

MonoRepo What and when

A monorepo is a repository consisting of multiple packages/packages which can be related but not necessary. Few of the famous monorepos are managed by Babel, Facebook, Google. Monolith !== monorepo. Monolith is huge amount of coupled code of 1 application that is hell to maintain.

Advantages

• Simplified organization.
• Easy to coordinate changes across modules.
• Simplified dependencies.
• Single lint, build, test and release process.
• Tooling.
• Single place to report issues
• Cross-project changes
• Tests across modules are run together → finds bugs that touch multiple modules easier

Steps with yarn and Lerna

• create a package.json file in root directory or just hit npm init.
• Add private: true in package.json to avoid accidental publishing of private repositories.
• Add workspaces: ["packages"] in package.json to add and access all the projects/packages.
• cd into the directories and hit yarn init -y
• Hit yarn install anywhere in the project mostly in the root directory, this creates a symklink i.e it creates a link between the package and generated packages in the node_modules
• To install lerna add yarn -D -W lerna where -D is for dev dependency alternatively can be installed with npm
• Hit npx lerna init --independent/-i (Use -i for independent versioning mode) and generate lerna repo.
• Add useWorkspaces: true and npmClient: yarn in lerna.json.
• Use lerna run <command name> to run command across all packages within the project
• We can add scoping with Lerna by using lerna run <command name --scope= @projectname/packagename> this should be same as that of package.json.
• Scoping can be done for multiple packages too example lerna run <command name --scope= {@projectname/pkg1, @projectname/pkg2}>.

Lerna Commands

• lerna init -
  Creates a new lerna repo or upgrade existing to lerna comes with --independent flag for independent versioning.

• lerna bootstrap -
  Bootstrap the packages in the current Lerna repo. Installing all their dependencies and linking any cross-dependencies. This command is crucial, as it allows you to use your package names in require() as if the packages were already existing and available in your node_modules folder.

• lerna run -
  Run an npm script in each package that contains that script. Alternatively, @scope can be used to run the command on the mentioned packages.

• lerna version -
  Bump version of packages changed since the last release. More here.
  When run, this command does the following:

  1. Identifies packages that have been updated since the previous tagged release.
  2. Prompts for a new version.
  3. Modifies package metadata to reflect new release.
  4. Commits those changes and tags the commit.
  5. Pushes to the git remote.

• lerna publish -
  Publish packages in the current project. More Options

• lerna changed -
  Check which packages have changed since the last release.

• lerna diff -
  Diff all packages or a single package since the last release.More