mirror of
https://github.com/oven-sh/bun
synced 2026-02-02 15:08:46 +00:00
37c41137f8
## Summary
Add a new `replMode` option to `Bun.Transpiler` that transforms code for
interactive REPL evaluation. This enables building a Node.js-compatible
REPL using `Bun.Transpiler` with `vm.runInContext` for persistent
variable scope.
## Features
- **Expression result capture**: Wraps the last expression in `{
__proto__: null, value: expr }` for result capture
- **IIFE wrappers**: Uses sync/async IIFE wrappers to avoid extra
parentheses around object literals in output
- **Variable hoisting**: Hoists `var`/`let`/`const` declarations outside
the IIFE for persistence across REPL lines
- **const → let conversion**: Converts `const` to `let` for REPL
mutability (allows re-declaration)
- **Function hoisting**: Hoists function declarations with
`this.funcName = funcName` assignment for vm context persistence
- **Class hoisting**: Hoists class declarations with `var` for vm
context persistence
- **Object literal detection**: Auto-detects object literals (code
starting with `{` without trailing `;`) and wraps them in parentheses
## Usage
```typescript
import vm from "node:vm";
const transpiler = new Bun.Transpiler({
loader: "tsx",
replMode: true,
});
const context = vm.createContext({ console, Promise });
async function repl(code: string) {
const transformed = transpiler.transformSync(code);
const result = await vm.runInContext(transformed, context);
return result.value;
}
// Example REPL session
await repl("var x = 10"); // 10
await repl("x + 5"); // 15
await repl("class Counter {}"); // [class Counter]
await repl("new Counter()"); // Counter {}
await repl("{a: 1, b: 2}"); // {a: 1, b: 2} (auto-detected object literal)
await repl("await Promise.resolve(42)"); // 42
```
## Transform Examples
| Input | Output |
|-------|--------|
| `42` | `(() => { return { __proto__: null, value: 42 }; })()` |
| `var x = 10` | `var x; (() => { return { __proto__: null, value: x =
10 }; })()` |
| `await fetch()` | `(async () => { return { __proto__: null, value:
await fetch() }; })()` |
| `{a: 1}` | `(() => { return { __proto__: null, value: ({a: 1}) };
})()` |
| `class Foo {}` | `var Foo; (() => { return { __proto__: null, value:
Foo = class Foo {} }; })()` |
## Files Changed
- `src/ast/repl_transforms.zig`: New module containing REPL transform
logic
- `src/ast/P.zig`: Calls REPL transforms after parsing in REPL mode
- `src/bun.js/api/JSTranspiler.zig`: Adds `replMode` config option and
object literal detection
- `src/options.zig`, `src/runtime.zig`, `src/transpiler.zig`: Propagate
`repl_mode` flag
- `packages/bun-types/bun.d.ts`: TypeScript type definitions
- `test/js/bun/transpiler/repl-transform.test.ts`: Test cases
## Testing
```bash
bun bd test test/js/bun/transpiler/repl-transform.test.ts
```
34 tests covering:
- Basic transform output
- REPL session with node:vm
- Variable persistence across lines
- Object literal detection
- Edge cases (empty input, comments, TypeScript, etc.)
- No-transform cases (await inside async functions)
---------
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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.