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Rollup is a module bundler for JavaScript which compiles small pieces of code into something larger and more complex, such as a library or application. It uses the standardized ES module format for code, instead of previous idiosyncratic solutions such as CommonJS and AMD. ES modules let you freely and seamlessly combine the most useful individual functions from your favorite libraries. Rollup can optimize ES modules for faster native loading in modern browsers, or output a legacy module format allowing ES module workflows today.

Install withnpm install --global rollup. Rollup can be used either through acommand line interface with an optional configuration file or else through itsJavaScript API. Runrollup --help to see the available options and parameters. The starter project templates,rollup-starter-lib androllup-starter-app, demonstrate common configuration options, and more detailed instructions are available throughout theuser guide.

These commands assume the entry point to your application is named main.js, and that you'd like all imports compiled into a single file named bundle.js.

For browsers:

# compile to a <script> containing a self-executing functionrollup main.js --format iife --name"myBundle" --file bundle.js

For Node.js:

# compile to a CommonJS modulerollup main.js --format cjs --file bundle.js

For both browsers and Node.js:

# UMD format requires a bundle namerollup main.js --format umd --name"myBundle" --file bundle.js

Developing software is usually easier if you break your project into smaller separate pieces, since that often removes unexpected interactions and dramatically reduces the complexity of the problems you'll need to solve, and simply writing smaller projects in the first placeisn't necessarily the answer. Unfortunately, JavaScript has not historically included this capability as a core feature in the language.

This finally changed with ES modules support in JavaScript, which provides a syntax for importing and exporting functions and data so they can be shared between separate scripts. Most browsers and Node.js support ES modules. However, Node.js releases before 12.17 support ES modules only behind the--experimental-modules flag, and older browsers like Internet Explorer do not support ES modules at all. Rollup allows you to write your code using ES modules, and run your application even in environments that do not support ES modules natively. For environments that support them, Rollup can output optimized ES modules; for environments that don't, Rollup can compile your code to other formats such as CommonJS modules, AMD modules, and IIFE-style scripts. This means that you get towrite future-proof code, and you also get the tremendous benefits of...

In addition to enabling the use of ES modules, Rollup also statically analyzes and optimizes the code you are importing, and will exclude anything that isn't actually used. This allows you to build on top of existing tools and modules without adding extra dependencies or bloating the size of your project.

For example, with CommonJS, theentire tool or library must be imported.

// import the entire utils object with CommonJSvarutils=require('node:utils');varquery='Rollup';// use the ajax method of the utils objectutils.ajax('https://api.example.com?search='+query).then(handleResponse);

But with ES modules, instead of importing the wholeutils object, we can just import the oneajax function we need:

// import the ajax function with an ES import statementimport{ajax}from'node:utils';varquery='Rollup';// call the ajax functionajax('https://api.example.com?search='+query).then(handleResponse);

Because Rollup includes the bare minimum, it results in lighter, faster, and less complicated libraries and applications. Since this approach is based on explicitimport andexport statements, it is vastly more effective than simply running an automated minifier to detect unused variables in the compiled output code.

Rollup can import existing CommonJS modulesthrough a plugin.

To make sure your ES modules are immediately usable by tools that work with CommonJS such as Node.js and webpack, you can use Rollup to compile to UMD or CommonJS format, and then point to that compiled version with themain property in yourpackage.json file. If yourpackage.json file also has amodule field, ES-module-aware tools like Rollup andwebpack willimport the ES module version directly.

This project exists thanks to all the people who contribute. [Contribute].. If you want to contribute yourself, head over to thecontribution guidelines.

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TNG has been supporting the work ofLukas Taegert-Atkinson on Rollup since 2017.

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