npm package: @mablemarket/monopack
Description: A JavaScript bundler for node.js monorepo applications
Author: Florent Le Gall
Latest version: 0.3.0

# Monopack

A JavaScript bundler for node.js monorepo-codebased applications.

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![Quality](https://img.shields.io/badge/quality-alpha-tomato.svg) [![lerna](https://img.shields.io/badge/maintained%20with-lerna-cc00ff.svg)](https://lernajs.io/) [![code style: prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg)](https://github.com/prettier/prettier)

This tool comes to fill a gap for node.js developpers who :

- are building node.js applications (serverless functions, micro-services, monolithic servers or client applications)
- are using a monorepo codebase.
- are performing continuous integration/deployment.

Monopack aims to build **a static deterministic deliverable bundle** from your application's entrypoint **main.js**.

It will build:

- **a single main.js** file that bundles all the imported sources from the monorepo.
- **package.json and yarn.lock** files including **only** the used third-party dependencies.
- the **node_modules directory** for these dependencies.

## Usage

### Requirements

- Node.js >= 6.14.4
- Yarn >= 1.3.2 :
  - Yarn is required to be present for installing the produced dependencies.
  - It is not mandatory for your project to use it, but bear in mind that the dependencies collection will be deterministic only if your projet uses Yarn.

### Installation

It can be installed globally and locally

#### Global installation

Using yarn

    yarn global add monopack

Or npm

    npm install -g monopack

You can then use it with

    $ monopack

#### Local installation

Using yarn

    yarn add -D monopack

Or npm

    npm install --save-dev monopack

You can then use it on your project

With yarn

    $ yarn run @mablemarket/monopack

With npm

    ./node_modules/.bin/monopack

### CLI

    monopack <command>

    Commands:
      monopack build main  Builds an application
      monopack run main    Runs an application
      monopack debug main  Runs an application in debug mode (Node >= v8 only)

    Options:
      --help                          Show help                            [boolean]
      --version                       Show version number                  [boolean]
      --watch, -w                     Enable watch mode   [boolean] [default: false]
      --out-dir, -d                   Output directory (default into a temp dir)
                                                                            [string]
      --no-packages-installation, -n  Do not install packages after build  [boolean]
      --install-packages, -i          Install packages after build         [boolean]
      --with-extra-module, -m         Adds an extra module to the dependencies.
                                      It can be useful for dynamically required
                                      dependencies that monopack cannot detect
                                      (e.g.: an sql driver).

                                      It expects the package name without the
                                      version. (e.g: 'mysql' not 'mysql@2.16.0).
                                      It can be use multiple times "monopack build
                                      main.js -m mysql -m postgresql" in order to
                                      provide multiple dependencies.

                                      Make sure to install it in the same package as
                                      the main file, otherwise another version might
                                      be picked up.                         [string]
      --debug-host-port               [host:]port setting to pass to node --inspect
                                      option.
                                      It must be used with the debug command.
                                                                            [string]
      --debug-break                   Break at start of main script.
                                      This option is required when you want to debug
                                      something that gets immediately executed when
                                      starting.
                                      It triggers the --inspect-brk node option.
                                      It must be used with the debug command.
                                                                          [boolean]

### Default configuration

By default monopack will use babel 7 to compile your code into js code that node.js 6.14.4 understands.
It supports [flow](https://flow.org) and [stage-2](https://github.com/babel/babel/tree/master/packages/babel-preset-stage-2) features.

```js
const baseBabelConfig = {
  presets: [
    [
      '@babel/preset-env',
      {
        targets: {
          node: '6.14.4',
        },
      },
    ],
    '@babel/preset-flow',
  ],
  plugins: [
    ['@babel/plugin-proposal-decorators', { legacy: true }],
    '@babel/plugin-proposal-function-sent',
    '@babel/plugin-proposal-export-namespace-from',
    '@babel/plugin-proposal-numeric-separator',
    '@babel/plugin-proposal-throw-expressions',
    '@babel/plugin-syntax-dynamic-import',
    '@babel/plugin-syntax-import-meta',
    ['@babel/plugin-proposal-class-properties', { loose: false }],
    '@babel/plugin-proposal-json-strings',
  ],
};
```

Monopack will use webpack 4 to produce the bundle.
The bundle is produced in 'development' mode in order not to obfuscate the code.
Source maps are included.

### Configuration file

You can include an optional configuration file : **monopack.config.js**

This configuration file can be used to :

- Define the monorepo root
- Override the default babel configuration
- Override the default webpack configuration

You can use multiple configuration files, have a top-level one that the top of the monorepo and have a more specific one per package. More specific entries will override the ones from the root. If you would like to combine then, you have to require the parent configuration file and implement the merge operation on your own.

The config file can export the following entries :

- monorepoRootPath : the relative path to the monorepo root.
- outputDirectory: the relative or absolute path to the output directory (defaults to a temp file).
- babelConfigModifier : a function that takes the current configuration and returns the modified configuration.
- webpackConfigModifier: a function that takes the current configuration and returns the modified configuration.
- installPackagesAfterBuild : a boolean indicating whether packages should be installed after build (default to true).
- extraModules: an array of extra-module names to bundle (default empty). It can be useful for dynamically required dependencies that monopack cannot detect (e.g.: an sql driver).
  - It expects the package name without the version. (e.g: 'mysql' not 'mysql@2.16.0).
  - It can be use multiple times "monopack build main.js -m mysql -m postgresql" in order to provide multiple dependencies.
  - Make sure to install it in the same package as the main file, otherwise another version might be picked up.
- modifyPackageJson: a function that takes the produced package json and returns the modified package json object: it can be used to add extra info (engines, version).
- afterBuild: a function that gets executed when build is complete. It can be used to trigger something after your build has been produced.
  - This function takes the build directory as parameter.
  - This function can return a promise that will be awaited.

For example :

```js
module.exports.monorepoRootPath = '../..';
module.exports.outputDirectory = './build';
module.exports.babelConfigModifier = defaultBabelConfiguration => {
  return babelConfiguration(defaultBabelConfiguration);
};
module.exports.webpackConfigModifier = defaultWebpackConfig => {
  return webPackConfiguration(defaultWebpackConfig);
};
module.exports.installPackagesAfterBuild = true;
module.exports.extraModules = ['mysql', 'postgresql'];
module.exports.modifyPackageJson = pkg => ({ ...pkg, private: false });
module.exports.afterBuild = async buildDirectory => {
  return triggerActionAfterBuild(buildDirectory);
};
```

I encourage you not to modify the webpack configuration, as I intend to keep in track with latest webpack versions, having a custom webpack configuration will be difficult to update on your side.
If you have specific needs that require a customization please [open an issue](https://github.com/flegall/monopack/issues/new)

### Dependencies handling

Monopack will collect:

- all used dependencies (dependencies actually **imported** or **required()**).
- all peer dependencies of your used dependencies.

All the dependencies are collected, a package.json with the collected dependencies will be compiled.

Your project's yarn.lock will be copied if it exists.
If you are using multiple yarn.lock files, only the top-most one will be copied.

The dependencies collection is **deterministic** only if you have a single yarn.lock file.
In order to achieve that you can :

- Use [yarn's workspaces](https://yarnpkg.com/lang/en/docs/workspaces/)
- Declare your dependencies in a single package.json file.

## Why such a tool ?

As far as I know such a tool does not exist so far.

### Monorepos and node.js

[Many developpers](https://github.com/babel/babel/blob/master/doc/design/monorepo.md#previous-discussion) (me included) tend to consider that the only viable way of performing continous integration is to use a monorepo.

I personally find it very practical :

- Pros:
  - Code sharing is **a lot easier**
  - You have a **single lint, build, test and release process**.
  - It's **easy to coordinate changes** across modules.
  - It's easier to setup a development environment.
  - Tests across modules are ran together which finds bugs that touch multiple modules easier.
- Median:
  - It forces you to perform continous integration. This is generally a very good thing, but it requires some maturity within your team and your test/release process. Of course a mono-repo does not force you to perform continous integration, but I think that releasing frequently from a mono-repo without a decent automated testing strategy is quite risky !
- Cons:
  - Codebase looks more intimidating.
  - Repo is bigger in size.

Unfortunately, this is not currently a very popular trend amongst many Node.JS developpers and micro-services developpers.

The classical tooling in Node.JS is designed for delivering open-source libraries and not organizing for mono-repos :

- NPM initially did not provide a way to have multiple package.json within the same repository and create dependencies between then.
- [LernaJS](https://lernajs.io/) proposed a way to support mono-repos for open-source libraries.
- [Yarn](https://yarnpkg.com/lang/en/docs/workspaces/) proposes workspaces which makes dependency management convenient on a mono-repo.

When deploying a node.js application (either within a container, or within a PAAS or on physical/virtual machine), you would like to rely on NPM/Yarn to install the application dependencies and rely on your "start" script to execute your application.

But how to bundle your application from your mono-repo sources to a static deliverable package ?

That's the purpose of monopack !

### Some alternatives

You can usedversions and make [LernaJS](https://lernajs.io/) manage versions :

- You would:
  - bundle each of your monorepo internal dependencies as a Lerna package (optionally, you can bundle the package with babel or webpack),
  - update the versions, like you would do for open-source software
  - publish each version to a private registry.
- This is maybe acceptable if you do not intend to perform continuous integration / continuous deployment (ci/cd) as Lerna can help you to automate publication.
- If you're performing ci/cd, updating the versions for building a new version is a pain you do not want to have or automate.
- It also makes your execution environment in development quite different from your release execution, as you would use symlinked modules in your run/debug environment and published modules in your release execution.

You could bring your whole monorepo in your application release :

- This will work, but it's not optimal:
  - it will include all your source and will require all your monorepo node_modules, it will increase your deployment time & cost. On one of my previous job, we relied on this, we ended up bundling react-native in each of our node.js's microservice's docker image :(
- If you are compiling your javascript code (using flow, typescript, or unsupported ES features: you still have to compile your code :

  - You could use [babel-node](https://babeljs.io/docs/usage/cli/#babel-node) to execute your main.js file. Babel-node will compile it on the fly.

    - This works, but it's not optimal, it requires a lot more memory in order to compile, startup time is increased, and as stated on [babel-node](https://babeljs.io/docs/usage/cli/#babel-node) : _"You should not be using babel-node in production"_

  - You could use [Webpack](https://webpack.js.org/) to bundle your main.js entrypoint and bundle all your used dependencies like you would do with web bundles.

    - Theorically this will work, however in practice it doesn't work, as some node.js modules are not designed to work like this :
      - Some modules rely on non-constant require() calls, so they won't be bundled
      - Some modules actually load some config files at runtime time using \_\_filename or \_\_dirname, and therefore the bundle will only work on the machine they were build.

  - You could use [Webpack](https://webpack.js.org/) to bundle your main.js entrypoint and rely on [Node externals](https://www.npmjs.com/package/webpack-node-externals) to avoid packaging the node_modules in webpack. Actually that's what [Backpack](https://github.com/jaredpalmer/backpack) does.
    - This will generate a single main.js file that includes only the sources that are imported. This is what monopack does, but you will still have to install all your monorepo dependencies.

## Contributing

See [CONTRIBUTING](CONTRIBUTING.md)

## Roadmap

See [issues labelled as enhancement](https://github.com/flegall/monopack/issues?q=is%3Aopen+is%3Aissue+label%3Aenhancement)