# Rollup

> Rollup ES module bundler. Use for library bundling.

- Skill: `majiayu000/rollup-2` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/rollup-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/rollup-2/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/rollup-2

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# Rollup

Rollup (v4) is the bundler of choice for **libraries**. It produces smaller, cleaner code than Webpack and pioneered Tree Shaking.

## When to Use

- **NPM Packages**: Building a library for others to use.
- **Flat Bundling**: "Scope Hoisting" puts everything in one closure for performance.

## Core Concepts

### Tree Shaking

Rollup analyzes the import graph and excludes unused code statically.

### Formats

Outputs `esm`, `cjs`, `umd`, `iife`.

### Plugins

The ecosystem that Vite adopted.

## Best Practices (2025)

**Do**:

- **Use `pkg.exports`**: Configure `package.json` exports correctly for ESM/CJS dual publish.
- **Externalize dependencies**: Don't bundle `react` into your library. Mark it as external.

**Don't**:

- **Don't use for Apps**: Use Vite (which uses Rollup internally) for apps. Use Rollup directly for libs.

## References

- [Rollup Documentation](https://rollupjs.org/)