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lerna

Description

:dragon: A tool for managing JavaScript projects with multiple packages.

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Lerna

A tool for managing JavaScript projects with multiple packages.

NPM Status CI Status

About

Splitting up large codebases into separate independently versioned packages is extremely useful for code sharing. However, making changes across many repositories is messy and difficult to track, and testing across repositories becomes complicated very quickly.

To solve these (and many other) problems, some projects will organize their codebases into multi-package repositories (sometimes called monorepos). Projects like Babel, React, Angular, Ember, Meteor, Jest, and many others develop all of their packages within a single repository.

Lerna is a tool that optimizes the workflow around managing multi-package repositories with git and npm.

Lerna can also reduce the time and space requirements for numerous copies of packages in development and build environments - normally a downside of dividing a project into many separate NPM packages. See the hoist documentation for details.

What does a Lerna repo look like?

There's actually very little to it. You have a file structure that looks like this:

my-lerna-repo/
  package.json
  packages/
    package-1/
      package.json
    package-2/
      package.json

What can Lerna do?

The two primary commands in Lerna are

lerna bootstrap
and
lerna publish
.

bootstrap
will link dependencies in the repo together.
publish
will help publish any updated packages.

What can't Lerna do?

Lerna is not a deployment tool for serverless monorepos. Hoisting might be incompatible with traditional serverless monorepo deployment techniques.

Getting Started

The instructions below are for Lerna 3.x. We recommend using it instead of 2.x for a new Lerna project.

Let's start by installing Lerna as a dev dependency of your project with npm.

$ mkdir lerna-repo && cd $_
$ npx lerna init

This will create a

lerna.json
configuration file as well as a
packages
folder, so your folder should now look like this:
lerna-repo/
  packages/
  package.json
  lerna.json

How It Works

Lerna allows you to manage your project using one of two modes: Fixed or Independent.

Fixed/Locked mode (default)

Fixed mode Lerna projects operate on a single version line. The version is kept in the

lerna.json
file at the root of your project under the
version
key. When you run
lerna publish
, if a module has been updated since the last time a release was made, it will be updated to the new version you're releasing. This means that you only publish a new version of a package when you need to.

Note: If you have a major version zero, all updates are considered breaking. Because of that, running

lerna publish
with a major version zero and choosing any non-prerelease version number will cause new versions to be published for all packages, even if not all packages have changed since the last release.

This is the mode that Babel is currently using. Use this if you want to automatically tie all package versions together. One issue with this approach is that a major change in any package will result in all packages having a new major version.

Independent mode

lerna init --independent

Independent mode Lerna projects allows maintainers to increment package versions independently of each other. Each time you publish, you will get a prompt for each package that has changed to specify if it's a patch, minor, major or custom change.

Independent mode allows you to more specifically update versions for each package and makes sense for a group of components. Combining this mode with something like semantic-release would make it less painful. (There is work on this already at atlassian/lerna-semantic-release).

Set the

version
key in
lerna.json
to
independent
to run in independent mode.

Troubleshooting

If you encounter any issues while using Lerna please check out our Troubleshooting document where you might find the answer to your problem.

Frequently asked questions

See FAQ.md.

Concepts

Lerna will log to a

lerna-debug.log
file (same as
npm-debug.log
) when it encounters an error running a command.

Lerna also has support for scoped packages.

Run

lerna --help
to see all available commands and options.

lerna.json

{
  "version": "1.1.3",
  "npmClient": "npm",
  "command": {
    "publish": {
      "ignoreChanges": ["ignored-file", "*.md"],
      "message": "chore(release): publish",
      "registry": "https://npm.pkg.github.com"
    },
    "bootstrap": {
      "ignore": "component-*",
      "npmClientArgs": ["--no-package-lock"]
    }
  },
  "packages": ["packages/*"]
}
  • version
    : the current version of the repository.
  • npmClient
    : an option to specify a specific client to run commands with (this can also be specified on a per command basis). Change to
    "yarn"
    to run all commands with yarn. Defaults to "npm".
  • command.publish.ignoreChanges
    : an array of globs that won't be included in
    lerna changed/publish
    . Use this to prevent publishing a new version unnecessarily for changes, such as fixing a
    README.md
    typo.
  • command.publish.message
    : a custom commit message when performing version updates for publication. See @lerna/version for more details.
  • command.publish.registry
    : use it to set a custom registry url to publish to instead of npmjs.org, you must already be authenticated if required.
  • command.bootstrap.ignore
    : an array of globs that won't be bootstrapped when running the
    lerna bootstrap
    command.
  • command.bootstrap.npmClientArgs
    : array of strings that will be passed as arguments directly to
    npm install
    during the
    lerna bootstrap
    command.
  • command.bootstrap.scope
    : an array of globs that restricts which packages will be bootstrapped when running the
    lerna bootstrap
    command.
  • packages
    : Array of globs to use as package locations.

The packages config in

lerna.json
is a list of globs that match directories containing a
package.json
, which is how lerna recognizes "leaf" packages (vs the "root"
package.json
, which is intended to manage the dev dependencies and scripts for the entire repo).

By default, lerna initializes the packages list as

["packages/*"]
, but you can also use another directory such as
["modules/*"]
, or
["package1", "package2"]
. The globs defined are relative to the directory that
lerna.json
lives in, which is usually the repository root. The only restriction is that you can't directly nest package locations, but this is a restriction shared by "normal" npm packages as well.

For example,

["packages/*", "src/**"]
matches this tree:
packages/
├── foo-pkg
│   └── package.json
├── bar-pkg
│   └── package.json
├── baz-pkg
│   └── package.json
└── qux-pkg
    └── package.json
src/
├── admin
│   ├── my-app
│   │   └── package.json
│   ├── stuff
│   │   └── package.json
│   └── things
│       └── package.json
├── profile
│   └── more-things
│       └── package.json
├── property
│   ├── more-stuff
│   │   └── package.json
│   └── other-things
│       └── package.json
└── upload
    └── other-stuff
        └── package.json

Locating leaf packages under

packages/*
is considered a "best-practice", but is not a requirement for using Lerna.

Legacy Fields

Some

lerna.json
fields are no longer in use. Those of note include:

Common
devDependencies

Most

devDependencies
can be pulled up to the root of a Lerna repo with
lerna link convert

The above command will automatically hoist things and use relative

file:
specifiers.

Hoisting has a few benefits:

  • All packages use the same version of a given dependency
  • Can keep dependencies at the root up-to-date with an automated tool such as GreenKeeper
  • Dependency installation time is reduced
  • Less storage is needed

Note that

devDependencies
providing "binary" executables that are used by npm scripts still need to be installed directly in each package where they're used.

For example the

nsp
dependency is necessary in this case for
lerna run nsp
(and
npm run nsp
within the package's directory) to work correctly:
{
  "scripts": {
    "nsp": "nsp"
  },
  "devDependencies": {
    "nsp": "^2.3.3"
  }
}

Git Hosted Dependencies

Lerna allows target versions of local dependent packages to be written as a git remote url with a

committish
(e.g.,
#v1.0.0
or
#semver:^1.0.0
) instead of the normal numeric version range. This allows packages to be distributed via git repositories when packages must be private and a private npm registry is not desired.

Please note that lerna does not perform the actual splitting of git history into the separate read-only repositories. This is the responsibility of the user. (See this comment for implementation details)

// packages/pkg-1/package.json
{
  name: "pkg-1",
  version: "1.0.0",
  dependencies: {
    "pkg-2": "github:example-user/pkg-2#v1.0.0"
  }
}

// packages/pkg-2/package.json { name: "pkg-2", version: "1.0.0" }

In the example above,

  • lerna bootstrap
    will properly symlink
    pkg-2
    into
    pkg-1
    .
  • lerna publish
    will update the committish (
    #v1.0.0
    ) in
    pkg-1
    when
    pkg-2
    changes.

README Badge

Using Lerna? Add a README badge to show it off: lerna

[![lerna](https://img.shields.io/badge/maintained%20with-lerna-cc00ff.svg)](https://lerna.js.org/)

Wizard

If you prefer some guidance for cli (in case you're about to start using lerna or introducing it to a new team), you might like lerna-wizard. It will lead you through a series of well-defined steps:

lerna-wizard demo image

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