mirror of
https://github.com/oven-sh/bun
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1bfe5c6b37
## Summary
- Port md4c (CommonMark-compliant markdown parser) from C to Zig under
`src/md/`
- Three output modes:
- `Bun.markdown.html(input, options?)` — render to HTML string
- `Bun.markdown.render(input, callbacks?)` — render with custom
callbacks for each element
- `Bun.markdown.react(input, options?)` — render to a React Fragment
element, directly usable as a component return value
- React element creation uses a cached JSC Structure with
`putDirectOffset` for fast allocation
- Component overrides in `react()`: pass tag names as options keys to
replace default HTML elements with custom components
- GFM extensions: tables, strikethrough, task lists, permissive
autolinks, disallowed raw HTML tag filter
- Wire up `.md` as a bundler loader (via explicit `{ type: "md" }`)
## JavaScript API
### `Bun.markdown.html(input, options?)`
Renders markdown to an HTML string:
```js
const html = Bun.markdown.html("# Hello **world**");
// "<h1>Hello <strong>world</strong></h1>\n"
Bun.markdown.html("## Hello", { headingIds: true });
// '<h2 id="hello">Hello</h2>\n'
```
### `Bun.markdown.render(input, callbacks?)`
Renders markdown with custom JavaScript callbacks for each element. Each
callback receives children as a string and optional metadata, and
returns a string:
```js
// Custom HTML with classes
const html = Bun.markdown.render("# Title\n\nHello **world**", {
heading: (children, { level }) => `<h${level} class="title">${children}</h${level}>`,
paragraph: (children) => `<p>${children}</p>`,
strong: (children) => `<b>${children}</b>`,
});
// ANSI terminal output
const ansi = Bun.markdown.render("# Hello\n\n**bold**", {
heading: (children) => `\x1b[1;4m${children}\x1b[0m\n`,
paragraph: (children) => children + "\n",
strong: (children) => `\x1b[1m${children}\x1b[22m`,
});
// Strip all formatting
const text = Bun.markdown.render("# Hello **world**", {
heading: (children) => children,
paragraph: (children) => children,
strong: (children) => children,
});
// "Hello world"
// Return null to omit elements
const result = Bun.markdown.render("# Title\n\n\n\nHello", {
image: () => null,
heading: (children) => children,
paragraph: (children) => children + "\n",
});
// "Title\nHello\n"
```
Parser options can be included alongside callbacks:
```js
Bun.markdown.render("Visit www.example.com", {
link: (children, { href }) => `[${children}](${href})`,
paragraph: (children) => children,
permissiveAutolinks: true,
});
```
### `Bun.markdown.react(input, options?)`
Returns a React Fragment element — use it directly as a component return
value:
```tsx
// Use as a component
function Markdown({ text }: { text: string }) {
return Bun.markdown.react(text);
}
// With custom components
function Heading({ children }: { children: React.ReactNode }) {
return <h1 className="title">{children}</h1>;
}
const element = Bun.markdown.react("# Hello", { h1: Heading });
// Server-side rendering
import { renderToString } from "react-dom/server";
const html = renderToString(Bun.markdown.react("# Hello **world**"));
// "<h1>Hello <strong>world</strong></h1>"
```
#### React 18 and older
By default, `react()` uses `Symbol.for('react.transitional.element')` as
the `$$typeof` symbol, which is what React 19 expects. For React 18 and
older, pass `reactVersion: 18`:
```tsx
const el = Bun.markdown.react("# Hello", { reactVersion: 18 });
```
### Component Overrides
Tag names can be overridden in `react()`:
```tsx
Bun.markdown.react(input, {
h1: MyHeading, // block elements
p: CustomParagraph,
a: CustomLink, // inline elements
img: CustomImage,
pre: CodeBlock,
// ... h1-h6, p, blockquote, ul, ol, li, pre, hr, html,
// table, thead, tbody, tr, th, td,
// em, strong, a, img, code, del, math, u, br
});
```
Boolean values are ignored (not treated as overrides), so parser options
like `{ strikethrough: true }` don't conflict with component overrides.
### Options
```js
Bun.markdown.html(input, {
tables: true, // GFM tables (default: true)
strikethrough: true, // ~~deleted~~ (default: true)
tasklists: true, // - [x] items (default: true)
headingIds: true, // Generate id attributes on headings
autolinkHeadings: true, // Wrap heading content in <a> tags
tagFilter: false, // GFM disallowed HTML tags
wikiLinks: false, // [[wiki]] links
latexMath: false, // $inline$ and $$display$$
underline: false, // __underline__ (instead of <strong>)
// ... and more
});
```
## Architecture
### Parser (`src/md/`)
The parser is split into focused modules using Zig's delegation pattern:
| Module | Purpose |
|--------|---------|
| `parser.zig` | Core `Parser` struct, state, and re-exported method
delegation |
| `blocks.zig` | Block-level parsing: document processing, line
analysis, block start/end |
| `containers.zig` | Container management: blockquotes, lists, list
items |
| `inlines.zig` | Inline parsing: emphasis, code spans, HTML tags,
entities |
| `links.zig` | Link/image resolution, reference links, autolink
rendering |
| `autolinks.zig` | Permissive autolink detection (www, url, email) |
| `line_analysis.zig` | Line classification: headings, fences, HTML
blocks, tables |
| `ref_defs.zig` | Reference definition parsing and lookup |
| `render_blocks.zig` | Block rendering dispatch (code, HTML, table
blocks) |
| `html_renderer.zig` | HTML renderer implementing `Renderer` VTable |
| `types.zig` | Shared types: `Renderer` VTable, `BlockType`,
`SpanType`, `TextType`, etc. |
### Renderer Abstraction
Parsing is decoupled from output via a `Renderer` VTable interface:
```zig
pub const Renderer = struct {
ptr: *anyopaque,
vtable: *const VTable,
pub const VTable = struct {
enterBlock: *const fn (...) void,
leaveBlock: *const fn (...) void,
enterSpan: *const fn (...) void,
leaveSpan: *const fn (...) void,
text: *const fn (...) void,
};
};
```
Four renderers are implemented:
- **`HtmlRenderer`** (`src/md/html_renderer.zig`) — produces HTML string
output
- **`JsCallbackRenderer`** (`src/bun.js/api/MarkdownObject.zig`) — calls
JS callbacks for each element, accumulates string output
- **`ParseRenderer`** (`src/bun.js/api/MarkdownObject.zig`) — builds
React element AST with `MarkedArgumentBuffer` for GC safety
- **`JSReactElement`** (`src/bun.js/bindings/JSReactElement.cpp`) — C++
fast path for React element creation using cached JSC Structure +
`putDirectOffset`
## Test plan
- [x] 792 spec tests pass (CommonMark, GFM tables, strikethrough,
tasklists, permissive autolinks, GFM tag filter, wiki links, coverage,
regressions)
- [x] 114 API tests pass (`html()`, `render()`, `react()`,
`renderToString` integration, component overrides)
- [x] 58 GFM compatibility tests pass
```
bun bd test test/js/bun/md/md-spec.test.ts # 792 pass
bun bd test test/js/bun/md/md-render-api.test.ts # 114 pass
bun bd test test/js/bun/md/gfm-compat.test.ts # 58 pass
```
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>
Co-authored-by: SUZUKI Sosuke <sosuke@bun.com>
Co-authored-by: robobun <robobun@oven.sh>
Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Kirill Markelov <kerusha.chubko@gmail.com>
Co-authored-by: Ciro Spaciari <ciro.spaciari@gmail.com>
Co-authored-by: Alistair Smith <hi@alistair.sh>
Bun
Read the docs →
What is Bun?
Bun is an all-in-one toolkit for JavaScript and TypeScript apps. It ships as a single executable called bun.
At its core is the Bun runtime, a fast JavaScript runtime designed as a drop-in replacement for Node.js. It's written in Zig and powered by JavaScriptCore under the hood, dramatically reducing startup times and memory usage.
bun run index.tsx # TS and JSX supported out-of-the-box
The bun command-line tool also implements a test runner, script runner, and Node.js-compatible package manager. Instead of 1,000 node_modules for development, you only need bun. Bun's built-in tools are significantly faster than existing options and usable in existing Node.js projects with little to no changes.
bun test # run tests
bun run start # run the `start` script in `package.json`
bun install <pkg> # install a package
bunx cowsay 'Hello, world!' # execute a package
Install
Bun supports Linux (x64 & arm64), macOS (x64 & Apple Silicon) and Windows (x64).
Linux users — Kernel version 5.6 or higher is strongly recommended, but the minimum is 5.1.
x64 users — if you see "illegal instruction" or similar errors, check our CPU requirements
# with install script (recommended)
curl -fsSL https://bun.com/install | bash
# on windows
powershell -c "irm bun.sh/install.ps1 | iex"
# with npm
npm install -g bun
# with Homebrew
brew tap oven-sh/bun
brew install bun
# with Docker
docker pull oven/bun
docker run --rm --init --ulimit memlock=-1:-1 oven/bun
Upgrade
To upgrade to the latest version of Bun, run:
bun upgrade
Bun automatically releases a canary build on every commit to main. To upgrade to the latest canary build, run:
bun upgrade --canary
Quick links
-
Intro
-
Templating
-
CLI
-
Runtime
-
Package manager
-
Bundler
-
Test runner
-
Package runner
-
API
- HTTP server (
Bun.serve) - WebSockets
- Workers
- Binary data
- Streams
- File I/O (
Bun.file) - import.meta
- SQLite (
bun:sqlite) - PostgreSQL (
Bun.sql) - Redis (
Bun.redis) - S3 Client (
Bun.s3) - FileSystemRouter
- TCP sockets
- UDP sockets
- Globals
- $ Shell
- Child processes (spawn)
- Transpiler (
Bun.Transpiler) - Hashing
- Colors (
Bun.color) - Console
- FFI (
bun:ffi) - C Compiler (
bun:fficc) - HTMLRewriter
- Testing (
bun:test) - Cookies (
Bun.Cookie) - Utils
- Node-API
- Glob (
Bun.Glob) - Semver (
Bun.semver) - DNS
- fetch API extensions
- HTTP server (
Guides
-
Binary
- Convert a Blob to a string
- Convert a Buffer to a blob
- Convert a Blob to a DataView
- Convert a Buffer to a string
- Convert a Blob to a ReadableStream
- Convert a Blob to a Uint8Array
- Convert a DataView to a string
- Convert a Uint8Array to a Blob
- Convert a Blob to an ArrayBuffer
- Convert an ArrayBuffer to a Blob
- Convert a Buffer to a Uint8Array
- Convert a Uint8Array to a Buffer
- Convert a Uint8Array to a string
- Convert a Buffer to an ArrayBuffer
- Convert an ArrayBuffer to a Buffer
- Convert an ArrayBuffer to a string
- Convert a Uint8Array to a DataView
- Convert a Buffer to a ReadableStream
- Convert a Uint8Array to an ArrayBuffer
- Convert an ArrayBuffer to a Uint8Array
- Convert an ArrayBuffer to an array of numbers
- Convert a Uint8Array to a ReadableStream
-
Ecosystem
- Use React and JSX
- Use Gel with Bun
- Use Prisma with Bun
- Add Sentry to a Bun app
- Create a Discord bot
- Run Bun as a daemon with PM2
- Use Drizzle ORM with Bun
- Build an app with Nuxt and Bun
- Build an app with Qwik and Bun
- Build an app with Astro and Bun
- Build an app with Remix and Bun
- Build a frontend using Vite and Bun
- Build an app with Next.js and Bun
- Run Bun as a daemon with systemd
- Deploy a Bun application on Render
- Build an HTTP server using Hono and Bun
- Build an app with SvelteKit and Bun
- Build an app with SolidStart and Bun
- Build an HTTP server using Elysia and Bun
- Build an HTTP server using StricJS and Bun
- Containerize a Bun application with Docker
- Build an HTTP server using Express and Bun
- Use Neon Postgres through Drizzle ORM
- Server-side render (SSR) a React component
- Read and write data to MongoDB using Mongoose and Bun
- Use Neon's Serverless Postgres with Bun
-
HTMLRewriter
-
HTTP
- Hot reload an HTTP server
- Common HTTP server usage
- Write a simple HTTP server
- Configure TLS on an HTTP server
- Send an HTTP request using fetch
- Proxy HTTP requests using fetch()
- Start a cluster of HTTP servers
- Stream a file as an HTTP Response
- fetch with unix domain sockets in Bun
- Upload files via HTTP using FormData
- Streaming HTTP Server with Async Iterators
- Streaming HTTP Server with Node.js Streams
-
Install
- Add a dependency
- Add a Git dependency
- Add a peer dependency
- Add a trusted dependency
- Add a development dependency
- Add a tarball dependency
- Add an optional dependency
- Generate a yarn-compatible lockfile
- Configuring a monorepo using workspaces
- Install a package under a different name
- Install dependencies with Bun in GitHub Actions
- Using bun install with Artifactory
- Configure git to diff Bun's lockb lockfile
- Override the default npm registry for bun install
- Using bun install with an Azure Artifacts npm registry
- Migrate from npm install to bun install
- Configure a private registry for an organization scope with bun install
-
Process
-
Read file
-
Runtime
- Delete files
- Run a Shell Command
- Import a JSON file
- Import a TOML file
- Set a time zone in Bun
- Set environment variables
- Re-map import paths
- Delete directories
- Read environment variables
- Import a HTML file as text
- Install and run Bun in GitHub Actions
- Debugging Bun with the web debugger
- Install TypeScript declarations for Bun
- Debugging Bun with the VS Code extension
- Inspect memory usage using V8 heap snapshots
- Define and replace static globals & constants
- Codesign a single-file JavaScript executable on macOS
-
Streams
- Convert a ReadableStream to JSON
- Convert a ReadableStream to a Blob
- Convert a ReadableStream to a Buffer
- Convert a ReadableStream to a string
- Convert a ReadableStream to a Uint8Array
- Convert a ReadableStream to an array of chunks
- Convert a Node.js Readable to JSON
- Convert a ReadableStream to an ArrayBuffer
- Convert a Node.js Readable to a Blob
- Convert a Node.js Readable to a string
- Convert a Node.js Readable to an Uint8Array
- Convert a Node.js Readable to an ArrayBuffer
-
Test
- Spy on methods in
bun test - Bail early with the Bun test runner
- Mock functions in
bun test - Run tests in watch mode with Bun
- Use snapshot testing in
bun test - Skip tests with the Bun test runner
- Using Testing Library with Bun
- Update snapshots in
bun test - Run your tests with the Bun test runner
- Set the system time in Bun's test runner
- Set a per-test timeout with the Bun test runner
- Migrate from Jest to Bun's test runner
- Write browser DOM tests with Bun and happy-dom
- Mark a test as a "todo" with the Bun test runner
- Re-run tests multiple times with the Bun test runner
- Generate code coverage reports with the Bun test runner
- import, require, and test Svelte components with bun test
- Set a code coverage threshold with the Bun test runner
- Spy on methods in
-
Util
- Generate a UUID
- Hash a password
- Escape an HTML string
- Get the current Bun version
- Encode and decode base64 strings
- Compress and decompress data with gzip
- Sleep for a fixed number of milliseconds
- Detect when code is executed with Bun
- Check if two objects are deeply equal
- Compress and decompress data with DEFLATE
- Get the absolute path to the current entrypoint
- Get the directory of the current file
- Check if the current file is the entrypoint
- Get the file name of the current file
- Convert a file URL to an absolute path
- Convert an absolute path to a file URL
- Get the absolute path of the current file
- Get the path to an executable bin file
-
WebSocket
-
Write file
Contributing
Refer to the Project > Contributing guide to start contributing to Bun.
License
Refer to the Project > License page for information about Bun's licensing.