generate-package-json-webpack-plugin

For limiting the dependencies inside package.json to only those that are actually being used by your code.

Why generate a new package.json?

This plugin is useful for when you have a large source project for development / testing from which smaller Node.js projects are bundled for various deployments and applications. Such as Google Cloud Functions.

Or even just for bundling your regular Node.js server code, and knowing that your package.json is as lean as it can possibly be for that next deployment.

We all know how our development environments can get a bit messy... 😅

💾 Install

npm install generate-package-json-webpack-plugin --save-dev

🔌 Usage

const basePackage = {
  "name": "my-nodejs-module",
  "version": "1.0.0",
  "main": "./index.js",
  "engines": {
    "node": ">= 14"
  }
}

// inside your webpack configuration
plugins: [new GeneratePackageJsonPlugin(basePackage)],

That's pretty much it. The plugin will generate a new package.json file with all the dependencies your code uses. The versions for the detected dependencies are sourced directly from the modules inside node_modules.

N.B. This base package file is deliberately barren, as a base to build upon for our final output package.json- any dependencies listed inside of it will be set deliberately and interpretted differently by the generation process. See below for more information.

Important note on externals

The plugin only writes the dependencies of modules which are found in the input code and have been marked in externals inside of your Webpack config.

This is logical because if a module is not marked as an external module it is included in your final webpack bundle and hence wouldn't need to be installed as a dependency again on deployment.

Because of this, this plugin is best used in conjunction with something like webpack-node-externals, which you can use to make sure your node modules are not included with your final bundle.js, like so:

const nodeExternals = require("webpack-node-externals");

// inside your webpack config
externals: [nodeExternals({
    whitelist: [/^module-I-want-bundled/],
})],

As you can see, you can add modules that you deliberately do want bundled using the whitelist option.

Adding modules outside of your code (build modules etc.)

OR to deliberately set different versions of bundled dependencies, or as different dependency type (peerDependencies, for example)

Simply place those dependencies inside the basePackageValues object which represents the base of the new package.json to be created.

Keep the version number string empty ("") to have the plugin resolve the version. To use a version which is different, set the version string deliberately here.

const basePackageValues = {
  "name": "my-nodejs-module",
  "version": "1.0.0",
  "main": "./index.js",
  "scripts": {
    "start": "cross-var node --max-old-space-size=$NODE_JS_MAX_OLD_SPACE_SIZE ./server.js"
  }
  "engines": {
    "node": ">= 14"
  },
  devDependencies: {
    "cross-var": "^1.1.0",
    "cross-env": "",
  },
  peerDependencies: {
    "react" : "",
  }
}

In this example, cross-var has deliberately been set to version ^1.1.0, and regardless of what is actually installed it will use this version. cross-env however will pull its version number from node_modules.

This is mostly useful for adding dependencies which are required at runtime but which are not picked up in your webpack bundle. Such as cross-var in this example which injects environment variables into a run script in a cross-platform friendly way.

Note that the same behaviour applies to all types of dependencies (dependencies, devDependencies and peerDependencies). In this example react will have the same behaviour as cross-env, but rather than being placed inside the dependencies list in the output file, it will be placed inside the peerDependencies list.

Simple API

new GeneratePackageJsonPlugin(basePackage, options)

First argument: basePackage

( Required ) You should set the base values for your package.json file here. For example:

const basePackage = {
  "name": "my-nodejs-module",
  "version": "1.0.0",
  "main": "./bundle.js",
  "engines": {
    "node": ">= 14"
  }
}

This will be merged with the generated "dependencies": { ... } to form the final package.json distribution file.

Second argument: options

( Optional )

An object with the following structure:

  {
     debug: true,
     useInstalledVersions: true,
     resolveContextPaths: [__dirname],
     sourcePackageFilenames: [
       join(__dirname, "../other-workspace/package.json"),
     ],
     forceWebpackVersion: "webpack5",
     excludeDependencies: ["aws-sdk"],
  }

The options:

debug (default: false) : Enable to show some debugging information on how the plugin is finding dependencies and creating a new package.json.

useInstalledVersions (default: true) : Resolve node modules and use the exact version that is installed in your environment. This is useful to lock versions on production deployments. This is the default and easiest way to use the plugin, if this is not enabled then you should be providing package.json files in sourcePackageFilenames from which the plugin will source module versions.

resolveContextPaths: Context paths for the internal resolve behaviour that looks upwards for node_modules to pull the versions from. The current directory is the default, but if you have a monorepo, there are edge cases where defining multiple contexts could be useful.

sourcePackageFilenames : If the default useInstalledVersions option is set, then this is only used as a final fallback for finding versions. This is useful for mono-repos and projects where your dependencies in your code are not only defined from a single contextual project. If you share code between multiple projects or "workspaces" to be bundled into a final distribution project, you might want to set this option.

forceWebpackVersion (optional- by default the plugin will attempt to detect the version) : This can be set to one of: webpack4 or webpack5. If you are using a version of Webpack lower than 4- then set it to webpack4. This may help folks who are using Webpack in an environment where multiple versions might be present.

excludeDependencies : Here you can set any dependencies you absolutely never want in your output package.json file, even if they happen to be used by your code. This is useful in some edge cases, such as where an execution environment provides these dependencies for you automatically, without installation required.

🔍 Things to take note of

You should remember to set the "main": "./index.js" to the correct filename (would probably be the output bundle file from the same webpack task), and / or correctly set your starting script which will be run on Node.js server deployments by npm start. You can set these values in the basePackage object you pass into the plugin, example:

const basePackage = {
  "name": "my-nodejs-module",
  "version": "1.0.0",
  "main": "./bundle.js",
  "scripts": {
    "start": "node ./bundle.js"
  },
  "engines": {
    "node": ">= 14"
  }
}