Bun Bundler

# Bun Bundler

Bun's bundler is a fast JavaScript/TypeScript bundler built on the same engine as Bun's runtime. It's an esbuild-compatible alternative with native performance.

## Quick Start

### CLI

```bash
# Basic bundle
bun build ./src/index.ts --outdir ./dist

# Production build
bun build ./src/index.ts --outdir ./dist --minify

# Multiple entry points
bun build ./src/index.ts ./src/worker.ts --outdir ./dist
```

### JavaScript API

```typescript
const result = await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
});

if (!result.success) {
  console.error("Build failed:", result.logs);
}
```

## Bun.build Options

```typescript
await Bun.build({
  // Entry points (required)
  entrypoints: ["./src/index.ts"],

  // Output directory
  outdir: "./dist",

  // Target environment
  target: "browser",  // "browser" | "bun" | "node"

  // Output format
  format: "esm",  // "esm" | "cjs" | "iife"

  // Minification
  minify: true,  // or { whitespace: true, identifiers: true, syntax: true }

  // Code splitting
  splitting: true,

  // Source maps
  sourcemap: "external",  // "none" | "inline" | "external" | "linked"

  // Naming patterns
  naming: {
    entry: "[dir]/[name].[ext]",
    chunk: "[name]-[hash].[ext]",
    asset: "[name]-[hash].[ext]",
  },

  // Define globals
  define: {
    "process.env.NODE_ENV": JSON.stringify("production"),
  },

  // External packages
  external: ["react", "react-dom"],

  // Loaders
  loader: {
    ".svg": "text",
    ".png": "file",
  },

  // Plugins
  plugins: [myPlugin],

  // Root directory
  root: "./src",

  // Public path for assets
  publicPath: "/static/",
});
```

## CLI Flags

```bash
bun build <entrypoints> [flags]
```

| Flag | Description |
|------|-------------|
| `--outdir` | Output directory |
| `--outfile` | Output single file |
| `--target` | `browser`, `bun`, `node` |
| `--format` | `esm`, `cjs`, `iife` |
| `--minify` | Enable minification |
| `--minify-whitespace` | Minify whitespace only |
| `--minify-identifiers` | Minify identifiers only |
| `--minify-syntax` | Minify syntax only |
| `--splitting` | Enable code splitting |
| `--sourcemap` | `none`, `inline`, `external`, `linked` |
| `--external` | Mark packages as external |
| `--define` | Define compile-time constants |
| `--loader` | Custom loaders for extensions |
| `--public-path` | Public path for assets |
| `--root` | Root directory |
| `--entry-naming` | Entry point naming pattern |
| `--chunk-naming` | Chunk naming pattern |
| `--asset-naming` | Asset naming pattern |

## Target Environments

### Browser (default)

```typescript
await Bun.build({
  entrypoints: ["./src/index.ts"],
  target: "browser",
  outdir: "./dist",
});
```

### Bun Runtime

```typescript
await Bun.build({
  entrypoints: ["./src/server.ts"],
  target: "bun",
  outdir: "./dist",
});
```

### Node.js

```typescript
await Bun.build({
  entrypoints: ["./src/server.ts"],
  target: "node",
  outdir: "./dist",
});
```

## Code Splitting

```typescript
await Bun.build({
  entrypoints: ["./src/index.ts", "./src/admin.ts"],
  splitting: true,
  outdir: "./dist",
});
```

Shared dependencies are extracted into separate chunks automatically.

## Loaders

| Loader | Extensions | Output |
|--------|------------|--------|
| `js` | `.js`, `.mjs`, `.cjs` | JavaScript |
| `jsx` | `.jsx` | JavaScript |
| `ts` | `.ts`, `.mts`, `.cts` | JavaScript |
| `tsx` | `.tsx` | JavaScript |
| `json` | `.json` | JavaScript |
| `toml` | `.toml` | JavaScript |
| `text` | - | String export |
| `file` | - | File path export |
| `base64` | - | Base64 string |
| `dataurl` | - | Data URL |
| `css` | `.css` | CSS file |

Custom loaders:

```typescript
await Bun.build({
  entrypoints: ["./src/index.ts"],
  loader: {
    ".svg": "text",
    ".png": "file",
    ".woff2": "file",
  },
});
```

## Plugins

```typescript
const myPlugin = {
  name: "my-plugin",
  setup(build) {
    // Resolve hook
    build.onResolve({ filter: /\.special$/ }, (args) => {
      return { path: args.path, namespace: "special" };
    });

    // Load hook
    build.onLoad({ filter: /.*/, namespace: "special" }, (args) => {
      return {
        contents: `export default "special"`,
        loader: "js",
      };
    });
  },
};

await Bun.build({
  entrypoints: ["./src/index.ts"],
  plugins: [myPlugin],
});
```

## Build Output

```typescript
const result = await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
});

// Check success
if (!result.success) {
  for (const log of result.logs) {
    console.error(log);
  }
  process.exit(1);
}

// Access outputs
for (const output of result.outputs) {
  console.log(output.path);   // File path
  console.log(output.kind);   // "entry-point" | "chunk" | "asset"
  console.log(output.hash);   // Content hash
  console.log(output.loader); // Loader used

  // Read content
  const text = await output.text();
}
```

## Common Patterns

### Production Build

```typescript
await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  target: "browser",
  minify: true,
  sourcemap: "external",
  splitting: true,
  define: {
    "process.env.NODE_ENV": JSON.stringify("production"),
  },
});
```

### Library Build

```typescript
await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  target: "bun",
  format: "esm",
  external: ["*"],  // Externalize all dependencies
  sourcemap: "external",
});
```

### Build Script

```typescript
// build.ts
const result = await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  minify: process.env.NODE_ENV === "production",
});

if (!result.success) {
  console.error("Build failed");
  process.exit(1);
}

console.log(`Built ${result.outputs.length} files`);
```

Run: `bun run build.ts`

## Common Errors

| Error | Cause | Fix |
|-------|-------|-----|
| `Could not resolve` | Missing import | Install package or fix path |
| `No matching export` | Named export missing | Check export name |
| `Unexpected token` | Syntax error | Fix source code |
| `Target not supported` | Invalid target | Use `browser`, `bun`, or `node` |

## When to Load References

Load `references/options.md` when:
- Need complete option reference
- Configuring advanced features

Load `references/plugins.md` when:
- Writing custom plugins
- Understanding plugin API

Load `references/macros.md` when:
- Using compile-time macros
- Build-time code generation