@visulima/packem

Visulima Packem

A fast and modern bundler for Node.js and TypeScript.
Bundles anything that's supported by Node.js natively, namely .js, .json, .mjs, .cjs and TypeScript .ts, .cts, .mts, .tsx.

---

^{Daniel Bannert's open source work is supported by the community on GitHub Sponsors}

---

Overview

Visulima Packem is built on top of Rollup, combined with your preferred transformer like esbuild, swc, or sucrase. It enables you to generate multiple bundles (CommonJS or ESModule) simultaneously while adhering to Node.js’ native file type support.

It uses the exports configuration in package.json and recognizes entry file conventions to match your exports and build them into bundles.

Features

• ✅ package.json#exports, package.json#main, package.json#module to define entry-points
• ✅ package.json#bin to define executables
• ✅ package.json#types to define types
• ✅ Generates package.json#typeVersions to support node 10
• ✅ Dependency externalization
• ✅ Minification
• ✅ TypeScript support + .d.ts bundling
• ✅ Watch mode
• ✅ CLI outputs (auto hashbang insertion)
• ✅ Validates package.json and checks if all fields that are needed to publish your package are configured correctly
• ✅ Supports multiple runtimes (default, react-server, edge-light)
• ✅ Supports react server and client components
• ✅ Supports shared modules
• ✅ Supports dynamic import
• ✅ Supports tsconfig.json paths and package.json imports resolution
• ✅ ESM ⇄ CJS interoperability
• ✅ Supports isolated declaration types (experimental)
• ✅ Supports wasm WebAssembly modules

And more...

Install

npm install --save-dev @visulima/packem

yarn add -D @visulima/packem

pnpm add -D @visulima/packem

Prepare your project

You need to prepare your project to be able to bundle it with packem.

You can check out the following cases to configure your package.json.

JavaScript

Then use the exports field in package.json to configure different conditions and leverage the same functionality as other bundlers, such as webpack. The exports field allows you to define multiple conditions.

{
    "files": ["dist"],
    "exports": {
        "import": "./dist/index.mjs",
        "require": "./dist/index.cjs"
    },
    "scripts": {
        "build": "packem build"
    }
}

TypeScript

When building a TypeScript library, separate the types from the main entry file by specifying the types path in package.json. When you're using .mjs or .cjs extensions with TypeScript and modern module resolution (above node16), TypeScript will require specific type declaration files like .d.mts or .d.cts to match the extension. packem can automatically generate them to match the types to match the condition and extensions. One example is to configure your exports like this in package.json:

{
    "files": ["dist"],
    "exports": {
        "import": {
            "types": "./dist/index.d.mts",
            "default": "./dist/index.mjs"
        },
        "require": {
            "types": "./dist/index.d.cts",
            "default": "./dist/index.cjs"
        }
    },
    "scripts": {
        "build": "packem build"
    }
}

Hybrid (CJS & ESM) Module Resolution with TypeScript

If you're using TypeScript with Node 10 and Node 16 module resolution, you can use the types field in package.json to specify the types path. Then packem will generate the types file with the same extension as the main entry file.

{
    "files": ["dist"],
    "main": "./dist/index.cjs",
    "module": "./dist/index.mjs",
    "types": "./dist/index.d.ts",
    "exports": {
        "import": {
            "types": "./dist/index.d.mts",
            "default": "./dist/index.mjs"
        },
        "require": {
            "types": "./dist/index.d.cts",
            "default": "./dist/index.cjs"
        }
    },
    "scripts": {
        "build": "packem build"
    }
}

Enable the automatic node 10 typesVersions generation in packem.config.js:

export default defineConfig({
    // ...
    rollup: {
        // ...
        node10Compatibility: {
            typeScriptVersion: ">=5.0", // Chose the version of TypeScript you want to support
            writeToPackageJson: true,
        },
        // ...
    },
    transformer,
});

You can validate your package.json exports configuration with are the types wrong cli tool.

Links:

• https://github.com/frehner/modern-guide-to-packaging-js-library#set-the-main-field

Usage

Initialize the packem configuration

Initialize packem in your project, this will create a packem.config.ts or packem.config.js file in the root of your project.

packem init [options]

This command will ask you some questions about your project and create the configuration file.

Bundle files

Run the following command to bundle your files:

packem build [options]

Then files in src folders will be treated as entry files and match the export names in package.json.

[!NOTE] The src folder can be configured in the packem configuration file.

For example: src/index.ts will match the exports name "." or the only main export.

Now just run npm run build or pnpm build / yarn build if you're using these package managers, packem will find the entry files and build them. The output format will be based on the exports condition and also the file extension. Given an example:

• It's CommonJS for require and ESM for import based on the exports condition.
• It's CommonJS for .cjs and ESM for .mjs based on the extension regardless the exports condition. Then for export condition like "node" you could choose the format with your extension.

[!NOTE] All the dependencies and peerDependencies will be marked as external automatically and not included in the bundle. If you want to include them in the bundle, you can use the --no-external option.

This will write the files into the ./dist folder.

[!NOTE] The dist folder can be configured in the packem configuration file.

Multiple Runtime

For exports condition like react-native, react-server and edge-light as they're special platforms, they could have different exports or different code conditions. In this case packem provides an override input source file convention if you want to build them as different code bundle.

For instance:

{
    "exports": {
        "react-server": "./dist/react-server.mjs",
        "edge-light": "./dist/edge-light.mjs",
        "import": "./dist/index.mjs"
    }
}

[!NOTE] The edge-light export contains a process.env.EdgeRuntime variable true, for all other runtimes false is returned.

production and development exports condition

If you need to separate the production and development exports condition, packem provides process.env.NODE_ENV injected by default if present that you don't need to manually inject yourself.

• When the production exports condition is defined and the file ends with *.production.* in the package.json, the bundle will be minified.
• When the development exports condition is defined and the file ends with *.development.* in the package.json, the bundle will not be minified.

{
    "exports": {
        "development": "./dist/index.development.mjs",
        "production": "./dist/index.production.mjs"
    }
}

Executables

To build executable files with the bin field in package.json. The source file matching will be same as the entry files convention.

[!NOTE] > packem automatically preserves and prepends the shebang to the executable file, and fix correct permissions for the executable file.

For example:

|- src/
  |- bin/
    |- index.ts

This will match the bin field in package.json as:

{
    "bin": "./dist/bin/index.cjs"
}

or .mjs if the type field is module in package.json.

{
    "type": "module",
    "bin": "./dist/bin/index.mjs"
}

For multiple executable files, you can create multiple files.

|- src/
  |- bin/
    |- foo.ts
    |- bar.ts

This will match the bin field in package.json as:

{
    "bin": {
        "foo": "./dist/bin/foo.cjs",
        "bar": "./dist/bin/bar.cjs"
    }
}

Server Components

packem supports to build server components and server actions with library directives like "use client" or "use server". It will generate the corresponding chunks for client and server that scope the client and server boundaries properly. Then when the library is integrated to an app such as Next.js, app bundler can transform the client components and server actions correctly and maximum the benefits.

If you're using "use client" or "use server" in entry file, then it will be preserved on top and the dist file of that entry will become a client component. If you're using "use client" or "use server" in a file that used as a dependency for an entry, then that file containing directives be split into a separate chunk and hoist the directives to the top of the chunk.

Shared Modules (Experimental)

There are always cases that you need to share code among bundles, but they don't have to be a separate entry or exports. You want to have them bundled into a shared chunk and then use them in different bundles. You can use shared module convention [name].[layer]-runtime.[ext] to create shared modules bundles.

Shared Utils Example

// src/util.shared-runtime.js
export function sharedUtil() {
    /* ... */
}

Then you can use them in different entry files:

// src/index.js
import { sharedUtil } from "./util.shared-runtime";

// src/lite.js
import { sharedUtil } from "./util.shared-runtime";

packem will bundle the shared module into a separate layer which matches the file name convention, in the above case it's "shared", and that bundle will be referenced by the different entry bundles.

With multiple runtime bundles, such as having default and react-server together. They could have the modules that need to be shared and kept as only one instance among different runtime bundles. You can use the shared module convention to create shared modules bundles for different runtime bundles.

Shared Runtime Module Example

"use client";
// src/app-context.shared-runtime.js
export const AppContext = React.createContext(null);

Then you can use them in different entry files:

// src/index.js
import { AppContext } from "./app-context.shared-runtime";

// src/index.react-server.js
import { AppContext } from "./app-context.shared-runtime";

app-context.shared-runtime will be bundled into a separate chunk that only has one instance and be shared among different runtime bundles.

Text or Data Files

packem supports importing of file as string content, you can name the extension as .txt or .data, and it will be bundled as string content.

// src/index.js
import { text } from "./text.txt";

console.log(text); // "Hello World"

Visualize Bundle Makeup

Use the --visualize flag to generate a packem-bundle-analyze.html file at build time, showing the makeup of your bundle.

Building Module Workers (Experimental) (WIP)

packem supports building module workers with the --workers flag, which are a special type of bundle that can be used to run code in a web worker.

worker = new Worker(new URL("./worker.js", import.meta.url), { type: "module" });
// or simply:
worker = new Worker("./worker.js", { type: "module" });

CSS and CSS Modules (Coming Soon)

Aliases

Aliases can be configured in the import map, defined in package.json#imports.

For native Node.js import mapping, all entries must be prefixed with # to indicate an internal subpath import. Packem takes advantage of this behavior to define entries that are not prefixed with # as an alias.

Native Node.js import mapping supports conditional imports (eg. resolving different paths for Node.js and browser), but packem does not.

⚠️ Aliases are not supported in type declaration generation. If you need type support, do not use aliases.

{
    // ...

    imports: {
        // Mapping '~utils' to './src/utils.js'
        "~utils": "./src/utils.js",

        // Native Node.js import mapping (can't reference ./src)
        "#internal-package": "./vendors/package/index.js",
    },
}

ESM ⇄ CJS interoperability

Node.js ESM offers interoperability with CommonJS via static analysis. However, not all bundlers compile ESM to CJS syntax in a way that is statically analyzable.

Because packem uses Rollup, it's able to produce CJS modules that are minimal and interoperable with Node.js ESM.

This means you can technically output in CommonJS to get ESM and CommonJS support.

require() in ESM

Sometimes it's useful to use require() or require.resolve() in ESM. ESM code that uses require() can be seamlessly compiled to CommonJS, but when compiling to ESM, Node.js will error because require doesn't exist in the module scope.

When compiling to ESM, packem detects require() usages and shims it with createRequire(import.meta.url).

Not only does packem shim ESM ⇄ CJS, but fixes the export and export types for default exports in your commonjs files.

To enable both features you need to add cjsInterop: true to your packem config.

export default defineConfig({
    cjsInterop: true,
    // ...
});

Environment variables

Pass in compile-time environment variables with the --env flag.

This will replace all instances of process.env.NODE_ENV with 'production' and remove unused code:

packem build --env.NODE_ENV=production

Validating

Packem validates your package.json file and checks if all fields are configured correctly, that are needed to publish your package.

[!NOTE] To have a full validation checkup, visit publint and are the types wrong.

Configuration

packem.config.js

The packem configuration file is a JavaScript file that exports an object with the following properties:

transformer

You choose which one of the three supported transformer to use.

• esbuild
• @swc/core
• sucrase

Api Docs

Related

• bunchee - Zero config bundler for ECMAScript and TypeScript packages
• unbuild - 📦 An unified javascript build system
• pkgroll - 📦 Zero-config package bundler for Node.js + TypeScript
• siroc - Zero-config build tooling for Node
• tsup - The simplest and fastest way to bundle your TypeScript libraries
• microbundle - Zero-configuration bundler for tiny JS libs, powered by Rollup.

Supported Node.js Versions

Libraries in this ecosystem make the best effort to track Node.js’ release schedule. Here’s a post on why we think this is important.

Contributing

If you would like to help take a look at the list of issues and check our Contributing guild.

Note: please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Credits

• Daniel Bannert
• All Contributors

License

The visulima pack is open-sourced software licensed under the MIT