bun-src/docs/runtime/file-types.mdx

---
title: "File Types"
description: "File types and loaders supported by Bun's bundler and runtime"
---

The Bun bundler implements a set of default loaders. As a rule of thumb, the bundler and the runtime support the same set of file types.

`.js` `.cjs` `.mjs` `.mts` `.cts` `.ts` `.tsx` `.jsx` `.css` `.json` `.jsonc` `.json5` `.toml` `.yaml` `.yml` `.xml` `.txt` `.text` `.md` `.markdown` `.wasm` `.node` `.html` `.sh`

Bun uses the file extension to pick the built-in _loader_ that parses the file. Every loader has a name, such as `js`, `tsx`, or `json`. These names are used when building [plugins](/bundler/plugins) that extend Bun with custom loaders.

To specify a loader explicitly, use the `type` import attribute.

```ts
import my_toml from "./my_file" with { type: "toml" };
// or with dynamic imports
const { default: my_toml } = await import("./my_file", { with: { type: "toml" } });
```

---

## Built-in loaders

### `js`

**JavaScript**. Default for `.cjs` and `.mjs`.

Parses the code and applies a set of default transforms like dead-code elimination and tree shaking. Bun does not down-convert syntax.

### `jsx`

**JavaScript + JSX**. Default for `.js` and `.jsx`.

Same as the `js` loader, but JSX syntax is supported. By default, Bun down-converts JSX to plain JavaScript; the details depend on the `jsx*` compiler options in your `tsconfig.json`. Refer to the TypeScript documentation [on JSX](https://www.typescriptlang.org/docs/handbook/jsx.html).

### `ts`

**TypeScript loader**. Default for `.ts`, `.mts`, and `.cts`.

Strips out all TypeScript syntax, then behaves identically to the `js` loader. Bun does not perform typechecking.

### `tsx`

**TypeScript + JSX loader**. Default for `.tsx`. Transpiles both TypeScript and JSX to vanilla JavaScript.

### `json`

**JSON loader**. Default for `.json`.

JSON files can be directly imported.

```ts
import pkg from "./package.json";
pkg.name; // => "my-package"
```

During bundling, Bun inlines the parsed JSON into the bundle as a JavaScript object.

```ts
var pkg = {
  name: "my-package",
  // ... other fields
};
pkg.name;
```

If you pass a `.json` file as an entrypoint to the bundler, Bun converts it to a `.js` module that `export default`s the parsed object.

<CodeGroup>

```json Input
{
  "name": "John Doe",
  "age": 35,
  "email": "[email protected]"
}
```

```ts Output
export default {
  name: "John Doe",
  age: 35,
  email: "[email protected]",
};
```

</CodeGroup>

### `jsonc`

**JSON with Comments loader**. Default for `.jsonc`.

JSONC (JSON with Comments) files can be directly imported. Bun parses them, stripping out comments and trailing commas.

```ts
import config from "./config.jsonc";
console.log(config);
```

During bundling, Bun inlines the parsed JSONC into the bundle as a JavaScript object, identical to the `json` loader.

```ts
var config = {
  option: "value",
};
```

<Note>
  Bun automatically uses the `jsonc` loader for `tsconfig.json`, `jsconfig.json`, `package.json`, and `bun.lock` files.
</Note>

### `toml`

**TOML loader**. Default for `.toml`.

TOML files can be directly imported. Bun parses them with its fast native TOML parser.

```ts
import config from "./bunfig.toml";
config.logLevel; // => "debug"

// via import attribute:
// import myCustomTOML from './my.config' with {type: "toml"};
```

During bundling, Bun inlines the parsed TOML into the bundle as a JavaScript object.

```ts
var config = {
  logLevel: "debug",
  // ...other fields
};
config.logLevel;
```

If you pass a `.toml` file as an entrypoint, Bun converts it to a `.js` module that `export default`s the parsed object.

<CodeGroup>

```toml Input
name = "John Doe"
age = 35
email = "[email protected]"
```

```ts Output
export default {
  name: "John Doe",
  age: 35,
  email: "[email protected]",
};
```

</CodeGroup>

### `yaml`

**YAML loader**. Default for `.yaml` and `.yml`.

YAML files can be directly imported. Bun parses them with its fast native YAML parser.

```ts
import config from "./config.yaml";
console.log(config);

// via import attribute:
import data from "./data.txt" with { type: "yaml" };
```

During bundling, Bun inlines the parsed YAML into the bundle as a JavaScript object.

```ts
var config = {
  name: "my-app",
  version: "1.0.0",
  // ...other fields
};
```

If you pass a `.yaml` or `.yml` file as an entrypoint, Bun converts it to a `.js` module that `export default`s the parsed object.

<CodeGroup>

```yaml Input
name: John Doe
age: 35
email: [email protected]
```

```ts Output
export default {
  name: "John Doe",
  age: 35,
  email: "[email protected]",
};
```

</CodeGroup>

### `json5`

**JSON5 loader**. Default for `.json5`.

JSON5 files can be directly imported. Bun parses them with its fast native JSON5 parser. JSON5 is a superset of JSON that adds comments, trailing commas, unquoted keys, single-quoted strings, and more.

```ts
import config from "./config.json5";
console.log(config);

// via import attribute:
import data from "./data.txt" with { type: "json5" };
```

During bundling, Bun inlines the parsed JSON5 into the bundle as a JavaScript object.

```ts
var config = {
  name: "my-app",
  version: "1.0.0",
  // ...other fields
};
```

If you pass a `.json5` file as an entrypoint, Bun converts it to a `.js` module that `export default`s the parsed object.

<CodeGroup>

```json5 Input
{
  // Configuration
  name: "John Doe",
  age: 35,
  email: "[email protected]",
}
```

```ts Output
export default {
  name: "John Doe",
  age: 35,
  email: "[email protected]",
};
```

</CodeGroup>

### `xml`

**XML loader**. Default for `.xml`.

XML files can be directly imported. Bun parses them with its native XML 1.0 parser into the compact object shape of [`Bun.XML.parse`](/runtime/xml):

- One key for the root element
- `"@name"` keys for attributes
- Arrays for repeated child elements
- `"#text"` for text next to attributes or children
- Every value is a string

```ts
import doc from "./config.xml";
console.log(doc.config["@version"]);

// via import attribute:
import feed from "./export.rss" with { type: "xml" };
```

During bundling, Bun inlines the parsed XML into the bundle as a JavaScript object.

```ts
var doc = {
  config: {
    "@version": "2",
    // ...other fields
  },
};
```

If you pass a `.xml` file as an entrypoint, Bun converts it to a `.js` module that `export default`s the parsed object.

<CodeGroup>

```xml Input
<user id="1">
  <name>John Doe</name>
  <email>[email protected]</email>
  <role>admin</role>
  <role>editor</role>
</user>
```

```ts Output
export default {
  user: {
    "@id": "1",
    name: "John Doe",
    email: "[email protected]",
    role: ["admin", "editor"],
  },
};
```

</CodeGroup>

### `text`

**Text loader**. Default for `.txt` and `.text`.

Text files can be directly imported. Bun reads the file and returns it as a string.

```ts
import contents from "./file.txt";
console.log(contents); // => "Hello, world!"

// To import an html file as text
// The "type' attribute can be used to override the default loader.
import html from "./index.html" with { type: "text" };
```

When the file is referenced during a build, Bun inlines the contents into the bundle as a string.

```ts
var contents = `Hello, world!`;
console.log(contents);
```

If you pass a `.txt` file as an entrypoint, Bun converts it to a `.js` module that `export default`s the file contents.

<CodeGroup>

```txt Input
Hello, world!
```

```ts Output
export default "Hello, world!";
```

</CodeGroup>

### `md`

**Markdown loader**. Default for `.md` and `.markdown`.

Markdown files can be directly imported. Bun renders the file to HTML and returns the HTML as a string.

```ts
import html from "./README.md";
console.log(html); // => "<h1>Title</h1>\n"

// via import attribute (`markdown` is an alias of `md`):
import notes from "./notes.txt" with { type: "md" };
```

During bundling, Bun inlines the rendered HTML into the bundle as a string.

### `napi`

**Native addon loader**. Default for `.node`.

In the runtime, native addons can be directly imported.

```ts
import addon from "./addon.node";
console.log(addon);
```

In the bundler, Bun handles `.node` files using the [`file`](#file) loader.

### `sqlite`

**SQLite loader**. `with { "type": "sqlite" }` import attribute

In the runtime and bundler, SQLite databases can be directly imported. Bun loads the database with [`bun:sqlite`](/runtime/sqlite).

```ts
import db from "./my.db" with { type: "sqlite" };
```

The `sqlite` loader is only supported when the `target` is `bun`.

By default, the database is external to the bundle: Bun doesn't bundle the on-disk database file into the final output, so you can use a database loaded elsewhere.

You can change this behavior with the `"embed"` attribute:

```ts
// embed the database into the bundle
import db from "./my.db" with { type: "sqlite", embed: "true" };
```

With a [standalone executable](/bundler/executables), Bun embeds the database into the single-file executable.

Otherwise, the database to embed is copied into the `outdir` with a hashed filename.

### `html`

The `html` loader processes HTML files and bundles any referenced assets. It:

- Bundles and hashes referenced JavaScript files (`<script src="...">`)
- Bundles and hashes referenced CSS files (`<link rel="stylesheet" href="...">`)
- Hashes referenced images (`<img src="...">`)
- Preserves external URLs (by default, anything starting with `http://` or `https://`)

For example, given this HTML file:

<CodeGroup>

```html src/index.html
<!DOCTYPE html>
<html>
  <body>
    <img src="./image.jpg" alt="Local image" />
    <img src="https://example.com/image.jpg" alt="External image" />
    <script type="module" src="./script.js"></script>
  </body>
</html>
```

</CodeGroup>

Bun outputs a new HTML file with the bundled assets:

<CodeGroup>

```html dist/output.html
<!DOCTYPE html>
<html>
  <body>
    <img src="./image-HASHED.jpg" alt="Local image" />
    <img src="https://example.com/image.jpg" alt="External image" />
    <script type="module" src="./output-ALSO-HASHED.js"></script>
  </body>
</html>
```

</CodeGroup>

The loader uses [`lol-html`](https://github.com/cloudflare/lol-html) to extract script and link tags as entrypoints, and other assets as external.

The list of selectors is:

- `audio[src]`
- `img[src]`
- `img[srcset]`
- `link[as='font'][href], link[type^='font/'][href]`
- `link[as='image'][href]`
- `link[as='style'][href]`
- `link[as='video'][href], link[as='audio'][href]`
- `link[as='worker'][href]`
- `link[rel='icon'][href], link[rel='apple-touch-icon'][href]`
- `link[rel='manifest'][href]`
- `link[rel='stylesheet'][href]`
- `script[src]`
- `source[src]`
- `source[srcset]`
- `video[poster]`
- `video[src]`

<Note>

**HTML Loader Behavior in Different Contexts**

The `html` loader behaves differently depending on how it's used:

1. **Static Build:** When you run `bun build ./index.html`, Bun produces a static site with all assets bundled and hashed.

2. **Runtime:** When you run `bun run server.ts` (where `server.ts` imports an HTML file), Bun bundles assets on-the-fly during development, enabling features like hot module replacement.

3. **Full-stack Build:** When you run `bun build --target=bun server.ts` (where `server.ts` imports an HTML file), the import resolves to a manifest object that `Bun.serve` uses to efficiently serve pre-bundled assets in production.

</Note>

### `css`

**CSS loader**. Default for `.css`.

CSS files can be directly imported. This is primarily useful when [bundling HTML](/bundler/html-static#importing-css-in-javascript), where CSS is bundled alongside HTML.

```ts
import "./styles.css";
```

The import returns no value; it's only used for its side effects.

### `sh` loader

**Bun Shell loader**. Default for `.sh` files

This loader parses [Bun Shell](/runtime/shell) scripts. It's only supported when starting Bun itself, so it's not available in the bundler or in the runtime.

```sh
bun run ./script.sh
```

### `file`

**File loader**. Default for all unrecognized file types.

The file loader resolves the import as a _path/URL_ to the imported file. It's commonly used for referencing media or font assets.

```ts logo.ts
import logo from "./logo.svg";
console.log(logo);
```

_In the runtime_, Bun checks that the `logo.svg` file exists and resolves the import to its absolute path on disk.

```bash
bun run logo.ts
/path/to/project/logo.svg
```

_In the bundler_, Bun copies the file into `outdir` as-is, and the import resolves to a relative path pointing to the copied file.

```ts Output
var logo = "./logo.svg";
console.log(logo);
```

If `publicPath` is set, the import uses its value as a prefix to construct an absolute path/URL.

| Public path                  | Resolved import                    |
| ---------------------------- | ---------------------------------- |
| `""` (default)               | `./logo.svg`                       |
| `"/assets/"`                 | `/assets/logo.svg`                 |
| `"https://cdn.example.com/"` | `https://cdn.example.com/logo.svg` |

<Note>The value of [`naming.asset`](/bundler#naming) determines the location and file name of the copied file.</Note>

<Accordion title="Fixing TypeScript import errors">
If you're using TypeScript, you may get an error like this:

```ts
// TypeScript error
// Cannot find module './logo.svg' or its corresponding type declarations.
```

To fix this, create a `*.d.ts` file anywhere in your project (any name works) with the following contents:

```ts
declare module "*.svg" {
  const content: string;
  export default content;
}
```

This tells TypeScript to treat any default import from `.svg` as a string.

</Accordion>