Managing Packages Using a Monorepo

React Union - React for CMSs and Portals - Interview with Tomáš Konrády

npm packages can be managed in multiple ways. The most common way is to have one package per a source repository. The problems begin when you have to orchestrate changes across multiple related packages. The idea of monorepos was designed for this purpose.

Monorepos - What Are They#

A monorepo allows you to maintain multiple related packages within a single repository. Bigger projects, such as Babel or Jest, use this method for organizing their work. They use Lerna, a tool designed to help maintaining monorepos. Lerna can figure out what packages to update through changes and help with the versioning problem.

Lerna itself is quite opinionated and can be replaced with a package like mondorepo, oao, or custom scripts as Cycle.js has done.

Regardless of the technical solution, the idea is always similar. Your packages will exist with a predefined directory and you can maintain other directories at the same level for higher level documentation, examples, and a project site. You can also create package README files as a part of the site to avoid redundancy and to keep code quality high.

To give you an idea of a monorepo, consider the following structure from Reactabular, a project of mine:

.
├── docs/
├── lib/
├── node_modules/
├── packages
│   ├── reactabular-dnd
│   ├── reactabular-resizable
│   ├── reactabular-sticky
│   ├── reactabular-table
│   └── reactabular-virtualized
├── CHANGELOG.md
├── CONTRIBUTING.md
├── CONTRIBUTORS.md
├── LICENSE.md
├── README.md
├── lerna.json
├── package.json
└── webpack.config.babel.js

In practice there are more files and you can find more packages within the organization. I decided to push the core packages within this monorepo while I maintain secondary functionality not related strictly to it outside. A mixed model like this is one option.

Managing Separate Repositories#

Webpack is a popular project bundler. Managing the project comes with its own challenges. The project does not use a monorepo model. Instead, it has opted for organization based approach. It has two main organizations: one for the core and one for packages that complement the core — webpack-contrib.

Separating each package to a repository of its own makes them snowflakes in sense that each repository easily becomes different and it’s hard to keep them in sync if infrastructure evolves somehow. To solve the problem, webpack-defaults was developed.

The idea was to push project configuration (e.g. GitHub templates, linting, testing setup) to a single package that could be consumed across webpack-contrib repositories. When you install webpack-defaults to your project, it writes an npm script that pulls project defaults from the package and migrates the project as well it can to follow the standard.

Sometimes this can mean replacing entire file (i.e. Travis CI configuration) but there are times when patching the existing configuration is enough (i.e. .gitignore). This allows you to maintain control and it avoids customization per project following specific needs.

The biggest win of pushing shared configuration to a package like this is that it allows webpack to push project standards to a single place where they can be maintained. The changes can be consumed by running a single command at each project. This still requires inspection by programmers but it beats the alternative where it’s not possible to cascade changes across projects.

webpack-defaults relies on mrm-core for handling project level migrations. It’s at its best in patching configuration file formats like JSON or YAML. The problems begin if you have to patch JavaScript configuration as then the needed transformations become arbitrary given code can be written in so many ways. This is where codemods can come in for limited scenarios.

Conclusion#

Monorepos provide a refreshing alternative to managing each package per repository. They allow you to share the same configuration across separate packages and also coordinate related changes more easily. The approach comes with technical cost as performing this orchestration requires tooling.

Another option is to push the configuration problem to a package as was done in webpack-defaults. This way you can manage shared standards in a single place and share them across multiple projects.

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