Introduction to Monorepo in React
Tags: react, webdev, javascript, tutorial
Published: 2023-02-03 19:48:02

## Introduction

A monorepo, short for a monolithic repository. In software development, a monorepo is a strategy where code for multiple projects is stored in a single repository. In the context of a React frontend, a monorepo could contain multiple React projects, each representing a different feature or section of the application. This architectural pattern has become increasingly popular in recent years, and for good reason. Monorepo allows for easier code sharing and reuse, simplifies dependency management, and improves collaboration between teams working on different projects within the repo.
When it comes to building a React app, a monorepo architecture can be especially beneficial by housing all of your React projects within a single repository, you can centralize the management of shared libraries, scripts, and other resources, streamlining your development process and make it easier to maintain and scale your application over time.
In this article, we will explore the benefits of using a monorepo architecture for a React App, and provide a step-by-step guide on how to set up a monorepo using a tool like Lerna. We will also discuss when a monorepo may not be the best solution for your project, and help you evaluate if this architectural pattern is a good fit for your team and project.
It is important to note that the approach of monorepo is not a one-size-fits-all solution and it's important to evaluate the specific needs of your project and team before deciding on a monorepo architecture.

### Advantages of Monorepo

There are several advantages to using a monorepo architecture for software development:

- Code sharing and reuse: React components and libraries can be shared and reused between different projects within the monorepo, leading to more efficient development and a reduction in duplicated code.
- Simplified dependency management: A monorepo allows for centralized management of dependencies between projects. This makes it easier to keep track of which projects depend on which libraries and other resources, and to manage the versions of those dependencies.
- Improved collaboration: A monorepo can make it easier for teams working on different projects within the repository to collaborate and share knowledge. With all of the code in a single location, it's simpler for team members to understand the overall structure and organization of the codebase.
- Centralized management of resources: A monorepo allows for centralized management of shared libraries, scripts, and other resources. This can make it easier to maintain and scale the application over time.
- Easier testing and CI/CD: Having all the code in one place allows for more efficient testing and continuous integration and deployment.
- Better scalability: Monorepo allows for better scalability, as it makes it easy to add new projects, features and packages without any major changes to the existing structure.

### Disadvantage of Monorepo

While there are many advantages to using a monorepo architecture for React, there are also some potential disadvantages to consider:

- Increased complexity: A monorepo can add complexity to the development process, as it requires more advanced tools and workflows to manage the multiple projects within the repository.
- Slower performance: With a large monorepo, performance issues can arise as the number of files and dependencies increases. This can lead to slower build times and longer waiting times for developers to access the code they need.
- Higher risk of conflicts: With multiple projects and teams working within a single repository, the risk of conflicts and merge conflicts increases. These conflicts may lead to delays in the development process and can be difficult to resolve.
- Larger repository size: A monorepo can take up more storage space than a single repository. This could be an issue if you're working with limited storage space.
- Higher learning curve: Monorepo requires a certain level of knowledge and expertise in managing the different projects within the repository. This could be a disadvantage for new developers or teams that are not familiar with monorepo.
    
It's important to weigh the potential advantages and disadvantages of a monorepo architecture before implementing it in your React frontend project. It's also important to evaluate the specific needs of your project and team before deciding on a monorepo architecture.

## Prerequisite

There are a few prerequisites that you should have in order to understand the concepts discussed in this article on monorepo architecture for React:

- Familiarity with React: You should have a basic understanding of React and its components, as the article will focus on how to implement a monorepo architecture specifically for a React app.
- Experience with version control: Understanding of Git and basic version control concepts is necessary, as a monorepo is managed using a version control system like Git.
- Familiarity with package management: Knowledge of npm or yarn package manager is important, as the article will likely discuss how to manage dependencies within the monorepo.
- Familiarity with Lerna or similar tools is not required as the article will cover the introduction to the tool and how to use it.

### Monorepo Build Systems

Monorepo build systems are tools or software that are used to manage and build projects stored in a monorepo. A monorepo is a version control repository that contains multiple projects, typically in the form of packages, under a single version control repository. The purpose of a monorepo build system is to simplify the management of these packages and make it easier to share and reuse code across different projects.
Monorepo build systems to provide a range of functionality, including versioning, publishing, and managing inter-package dependencies. They also allow developers to manage dependencies, build processes, and test across multiple packages in a single repository, which simplifies the development process and reduces duplicated code.
There are several popular monorepo build systems available, including Lerna and Yarn Workspaces. Lerna is a popular tool for managing monorepos, and it provides features such as versioning, publishing, and managing inter-package dependencies. Yarn Workspaces, on the other hand, is a feature of the Yarn package manager that provides a way to manage multiple packages in a single repository.
When deciding whether to use a monorepo build system, there are several factors to consider, including the size and complexity of the project, the number of interdependent packages, and the development workflow. Monorepo build systems are often used in large-scale projects with multiple interdependent packages, as they simplify the management of these packages and make it easier to share code between packages.

### Lerna

Lerna is a popular tool for managing monorepo. It helps to simplify the management of multiple packages within a single repository. Lerna allows you to easily manage versioning, dependencies, and publishing of packages within a monorepo. 
Lerna provides a set of commands to help you manage your monorepo, such as:

- `lerna init`: Initialize a new or existing repository with Lerna.
- `lerna add`: Add a dependency to one or more packages.
- `lerna bootstrap`: Link-local packages together and install remaining package dependencies.
- `lerna run`: Runs npm script in each package that contains that script.
- `lerna publish`: Publish one or more packages.

Lerna has two modes of operation: fixed and independent mode. In fixed mode, all packages within the monorepo share a single version. In independent mode, each package can have its own version. This allows for more flexibility in the versioning and publishing of packages.
Lerna is highly configurable and can be integrated with other tools such as CircleCI, Travis, and Jenkins for continuous integration and deployment.

### Structure of a Monorepo

A monorepo typically consists of multiple packages, each representing a separate project or module. These packages are stored in a single repository, allowing developers to manage and share code and dependencies across different projects. The packages in a monorepo can be written in different languages, and they can depend on each other, making it easier to share and reuse code across different projects.
A typical monorepo structure might include the following components:

- Root directory: The root directory of the monorepo contains all of the packages, as well as configuration files for tools like Lerna or Yarn Workspaces.
- Packages: The packages are the individual projects or modules stored in the monorepo. Each package has its own directory, with its own source code, dependencies, and build scripts.
- Configuration files: The configuration files for tools like Lerna or Yarn Workspaces are stored in the root directory of the monorepo. These files specify how the packages should be built, tested, and published, as well as how they should depend on each other.
- Shared code: Some packages in the monorepo may depend on shared code, which can be stored in a separate directory or in one of the packages. This makes it easy to share code between packages and reduces duplicated code.
- Tests: Each package in the monorepo should have its own set of tests, which can be run independently or together as part of a larger test suite.

This is a general structure of a monorepo, and the specific structure of a monorepo can vary depending on the needs of the project. However, the overall goal is to simplify the management of multiple projects or modules by storing them in a single repository and to make it easier to share and reuse code across different projects.
Here's a simplified example of what a monorepo structure might look like:

```

monorepo/
|
|-- packages/
|   |
|   |-- package-a/
|   |   |
|   |   |-- src/
|   |   |-- test/
|   |   |-- package.json
|   |
|   |-- package-b/
|   |   |
|   |   |-- src/
|   |   |-- test/
|   |   |-- package.json
|   |
|   |-- shared-code/
|
|-- lerna.json
|-- yarn.lock

```

### Setting up a Monorepo

#### Initializing a new repository
The first step in setting up a monorepo is to create a new repository on a service like GitHub or GitLab. Initialize the repository with a README and a license.

#### Initializing Lerna
Navigate to the root of your new repository and run the following command to initialize Lerna:

```
    npx lerna@latest init
```

This command will create a new `lerna.json` file in the root of your repository, which contains Lerna's configuration settings. By default, Lerna is set to use the "independent" mode, which means that each package within the monorepo can have its own version.

#### Creating Packages

Next, you'll need to create the packages that will be part of your monorepo. These packages can be React components, utility functions, or any other code that you want to share across your project.
You can create a new package by running the following command:

```
    npx lerna create <package-name>
```

This will create a new directory in the `packages` directory, with the same name as the package you specified.

#### Adding dependencies

Once you've created your packages, you'll need to add dependencies between them. For example, if you have a package called `components` that contains your React components, and another package called `utils` that contains utility functions, you'll want to add a dependency from `components` to `utils` so that your components can access the utility functions. This can be done by using the `lerna add` command. 

```
   npx lerna add <package-name> --scope=<package-B>
```

Where `dependency-name` is the name of the package you want to add as a dependency, and `package-name` is the name of the package you want to add the dependency to.

#### Defining scripts

In order to automate tasks such as building, testing, and publishing your packages, you'll need to define scripts in the `package.json` file of each package. For example, you may want to define a script to build the package, another to test it, and another to publish it.

To build all of your packages, you can use the following command:

```
    npx lerna run build
```
To test all of your packages, you can use the following command:

```
   npx lerna run test
```

You can also build and test specific packages by specifying the package name after the command. For example, to build the `components` package, you would use the following command:

```
   npx lerna run build --scope=components
```
Configure Continuous Integration
Finally, once your packages are built and tested, you can use Lerna to publish them to npm or another package repository. To publish all of your packages, you can use the following command:

```
    npx lerna publish
```

You will be prompted to select a new version number and provide a description of the changes. Once this is done, Lerna will publish all of your packages to npm or the package repository you've configured.
If you'll want to configure continuous integration (CI) to automate the build, test and deployment process of your monorepo. You can use tools like CircleCI, Travis, and Jenkins to set up your pipeline.

## Conclusion

In conclusion, monorepo architecture can be a powerful tool for managing React frontend projects, and Lerna is a useful tool for setting up and maintaining a monorepo. This article has outlined the steps for setting up a monorepo with Lerna, including creating packages, adding dependencies, building and testing packages, and publishing them.
By using a monorepo, developers can share code and dependencies between packages, easily version and publish their packages, and manage dependencies at the monorepo level. This can help to simplify development, reduce duplicated code, and make it easier to share and reuse code across different projects.
Additionally, Lerna can automate many of the common tasks involved in maintaining a monorepo and make the management process much more efficient. However, it is important to note that a monorepo architecture may not be suitable for all projects, and it's important to evaluate the specific needs of a project before deciding to use a monorepo.
To learn more about monorepo architecture, Lerna and other related tools, readers can refer to the following resources:

- Lerna official documentation: [https://lerna.js.org](https://lerna.js.org/)
- React Monorepo guide: [https://www.robinwieruch.de/javascript-monorepos/](https://www.robinwieruch.de/javascript-monorepos/)
- React Monorepo with git-submodules: [https://dev.to/alexeagleson/how-to-create-a-node-and-react-monorepo-with-git-submodules-2g83](https://dev.to/alexeagleson/how-to-create-a-node-and-react-monorepo-with-git-submodules-2g83)
    

Overall, a monorepo with Lerna can be a powerful tool for managing React projects and streamlining the development process, but it's important to understand the specific needs of the project and be familiar with the tools and concepts involved.