# esbuild — Extremely Fast JavaScript Bundler

> esbuild is an extremely fast JavaScript/TypeScript bundler written in Go. 10-100x faster than webpack/Rollup. Powers Vite, Bun, and many modern build tools as their underlying transform engine.

## Install

Save the content below to `.claude/skills/` or append to your `CLAUDE.md`:

## Quick Use

```bash
npm i -D esbuild
```

CLI:
```bash
npx esbuild src/app.ts --bundle --outfile=dist/app.js \
  --platform=browser --target=es2020 --minify
```

JS API:
```js
import { build } from "esbuild";

await build({
  entryPoints: ["src/app.ts"],
  bundle: true,
  outfile: "dist/app.js",
  platform: "browser",
  target: "es2020",
  minify: true,
  sourcemap: true,
});
```

## Intro

esbuild is an extremely fast JavaScript/TypeScript bundler written in Go by Evan Wallace (Figma co-founder). Benchmark: bundles the three.js codebase (10K modules) in ~0.3s — compared to ~35s for webpack. Powers Vite, Bun, Snowpack, and many tools as their transform engine.

- **Repo**: https://github.com/evanw/esbuild
- **Stars**: 39K+
- **Language**: Go
- **License**: MIT

## What esbuild Does

- **Bundling** — merge modules into one file
- **TypeScript** — strip types (no type check)
- **JSX** — transform JSX to JS
- **Minification** — tree-shake + compress
- **Tree shaking** — remove unused exports
- **Source maps** — for debugging
- **Plugin API** — custom loaders and resolvers
- **Splitting** — code splitting for dynamic imports
- **Watch mode** — incremental rebuilds

## Architecture

Written in Go for parallelism (Go is 10x faster than JS for this kind of work + perfect concurrency). Parses, transforms, and prints all in one pass without intermediate AST serialization. No babel, no multiple plugins stacking up overhead.

## Self-Hosting

Bundled as a binary via npm. Ships in your build pipeline.

## Key Features

- 10-100x faster than webpack/Rollup
- TypeScript + JSX out of the box
- Tree shaking
- Minification
- Source maps
- CSS bundling (basic)
- Plugin API
- Incremental watch mode
- WASM build available

## Comparison

| Tool | Speed | Features | Plugins |
|---|---|---|---|
| esbuild | Fastest | Minimal | Limited |
| Rollup | Medium | Mature | Huge ecosystem |
| webpack | Slow | Most features | Huge ecosystem |
| Rolldown | Very fast | WIP | Rollup-compatible |
| Rspack | Very fast | webpack-compatible | webpack ecosystem |

## FAQ

**Q: Why is it so fast?**
A: Written in Go (native parallelism) + no intermediate AST + single-pass parse/transform/print + minimal plugin API. Evan wrote a detailed architecture doc.

**Q: Is it production-ready?**
A: Yes. Figma, Vite, and Bun all use it in production. It doesn't do type-checking, so pair it with a separate `tsc --noEmit` run.

**Q: What's its relationship with Vite?**
A: In dev mode Vite uses esbuild for dependency pre-bundling; for production it uses Rollup (because its plugin ecosystem is more mature).

## Sources & Credits

- Docs: https://esbuild.github.io
- GitHub: https://github.com/evanw/esbuild
- License: MIT

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Source: https://tokrepo.com/en/workflows/esbuild-extremely-fast-javascript-bundler-ee954487
Author: AI Open Source