bun-types

Bun is a new JavaScript & TypeScript runtime designed to be a faster, leaner, and more modern drop-in replacement for Node.js. ## Speed Bun is designed to start fast and run fast. Its transpiler and runtime are written in Zig, a modern, high-performance language. On Linux, this translates into startup times [4x faster](https://twitter.com/jarredsumner/status/1499225725492076544) than Node.js. {% image src="/images/bun-run-speed.jpeg" caption="Bun vs Node.js vs Deno running Hello World" /%}  Performance sensitive APIs like `Buffer`, `fetch`, and `Response` are heavily profiled and optimized. Under the hood Bun uses the [JavaScriptCore engine](https://developer.apple.com/documentation/javascriptcore), which is developed by Apple for Safari. It starts and runs faster than V8, the engine used by Node.js and Chromium-based browsers. ## TypeScript Bun natively supports TypeScript out of the box. All files are transpiled on the fly by Bun's fast native transpiler before being executed. Similar to other build tools, Bun does not perform typechecking; it simply removes type annotations from the file. ```bash $ bun index.js $ bun index.jsx $ bun index.ts $ bun index.tsx ``` Some aspects of Bun's runtime behavior are affected by the contents of your `tsconfig.json` file. Refer to [Runtime > TypeScript](https://bun.sh/docs/runtime/typescript) page for details.      ## JSX ## JSON and TOML Source files can import a `*.json` or `*.toml` file to load its contents as a plain old JavaScript object. ```ts import pkg from "./package.json"; import bunfig from "./bunfig.toml"; ``` ## WASI {% callout %} 🚧 **Experimental** {% /callout %} Bun has experimental support for WASI, the [WebAssembly System Interface](https://github.com/WebAssembly/WASI). To run a `.wasm` binary with Bun: ```bash $ bun ./my-wasm-app.wasm # if the filename doesn't end with ".wasm" $ bun run ./my-wasm-app.whatever ``` {% callout %} **Note** — WASI support is based on [wasi-js](https://github.com/sagemathinc/cowasm/tree/main/core/wasi-js). Currently, it only supports WASI binaries that use the `wasi_snapshot_preview1` or `wasi_unstable` APIs. Bun's implementation is not fully optimized for performance; this will become more of a priority as WASM grows in popularity. {% /callout %} ## Node.js compatibility Long-term, Bun aims for complete Node.js compatibility. Most Node.js packages already work with Bun out of the box, but certain low-level APIs like `dgram` are still unimplemented. Track the current compatibility status at [Ecosystem > Node.js](https://bun.sh/docs/runtime/nodejs-apis). Bun implements the Node.js module resolution algorithm, so dependencies can still be managed with `package.json`, `node_modules`, and CommonJS-style imports. {% callout %} **Note** — We recommend using Bun's [built-in package manager](https://bun.sh/docs/cli/install) for a performance boost over other npm clients. {% /callout %} ## Web APIs  Some Web APIs aren't relevant in the context of a server-first runtime like Bun, such as the [DOM API](https://developer.mozilla.org/en-US/docs/Web/API/HTML_DOM_API#html_dom_api_interfaces) or [History API](https://developer.mozilla.org/en-US/docs/Web/API/History_API). Many others, though, are broadly useful outside of the browser context; when possible, Bun implements these Web-standard APIs instead of introducing new APIs. The following Web APIs are partially or completely supported. {% table %} --- - HTTP - [`fetch`](https://developer.mozilla.org/en-US/docs/Web/API/fetch) [`Response`](https://developer.mozilla.org/en-US/docs/Web/API/Response) [`Request`](https://developer.mozilla.org/en-US/docs/Web/API/Request) [`Headers`](https://developer.mozilla.org/en-US/docs/Web/API/Headers) [`AbortController`](https://developer.mozilla.org/en-US/docs/Web/API/AbortController) [`AbortSignal`](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal) --- - URLs - [`URL`](https://developer.mozilla.org/en-US/docs/Web/API/URL) [`URLSearchParams`](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams) --- - Streams - [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream) [`WritableStream`](https://developer.mozilla.org/en-US/docs/Web/API/WritableStream) [`TransformStream`](https://developer.mozilla.org/en-US/docs/Web/API/TransformStream) [`ByteLengthQueuingStrategy`](https://developer.mozilla.org/en-US/docs/Web/API/ByteLengthQueuingStrategy) [`CountQueuingStrategy`](https://developer.mozilla.org/en-US/docs/Web/API/CountQueuingStrategy) and associated classes --- - Blob - [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob) --- - WebSockets - [`WebSocket`](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket) --- - Encoding and decoding - [`atob`](https://developer.mozilla.org/en-US/docs/Web/API/atob) [`btoa`](https://developer.mozilla.org/en-US/docs/Web/API/btoa) [`TextEncoder`](https://developer.mozilla.org/en-US/docs/Web/API/TextEncoder) [`TextDecoder`](https://developer.mozilla.org/en-US/docs/Web/API/TextDecoder) --- - Timeouts - [`setTimeout`](https://developer.mozilla.org/en-US/docs/Web/API/setTimeout) [`clearTimeout`](https://developer.mozilla.org/en-US/docs/Web/API/clearTimeout) --- - Intervals - [`setInterval`](https://developer.mozilla.org/en-US/docs/Web/API/setInterval)[`clearInterval`](https://developer.mozilla.org/en-US/docs/Web/API/clearInterval) --- - Crypto - [`crypto`](https://developer.mozilla.org/en-US/docs/Web/API/Crypto) [`SubtleCrypto`](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto) [`CryptoKey`](https://developer.mozilla.org/en-US/docs/Web/API/CryptoKey) --- - Debugging - [`console`](https://developer.mozilla.org/en-US/docs/Web/API/console) [`performance`](https://developer.mozilla.org/en-US/docs/Web/API/Performance) --- - Microtasks - [`queueMicrotask`](https://developer.mozilla.org/en-US/docs/Web/API/queueMicrotask) --- - Errors - [`reportError`](https://developer.mozilla.org/en-US/docs/Web/API/reportError) --- - User interaction - [`alert`](https://developer.mozilla.org/en-US/docs/Web/API/Window/alert) [`confirm`](https://developer.mozilla.org/en-US/docs/Web/API/Window/confirm) [`prompt`](https://developer.mozilla.org/en-US/docs/Web/API/Window/prompt) (intended for interactive CLIs)   --- - Realms - [`ShadowRealm`](https://github.com/tc39/proposal-shadowrealm) --- - Events - [`EventTarget`](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget) [`Event`](https://developer.mozilla.org/en-US/docs/Web/API/Event) [`ErrorEvent`](https://developer.mozilla.org/en-US/docs/Web/API/ErrorEvent) [`CloseEvent`](https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent) [`MessageEvent`](https://developer.mozilla.org/en-US/docs/Web/API/MessageEvent) --- {% /table %} ## Bun APIs Bun exposes a set of Bun-specific APIs on the `Bun` global object and through a number of built-in modules. These APIs represent the canonical "Bun-native" way to perform some common development tasks. They are all heavily optimized for performance. Click the link in the left column to view the associated documentation. {% table %} - Topic - APIs --- - [HTTP](https://bun.sh/docs/api/http) - `Bun.serve` --- - [File I/O](https://bun.sh/docs/api/file-io) - `Bun.file` `Bun.write` --- - [Processes](https://bun.sh/docs/api/spawn) - `Bun.spawn` `Bun.spawnSync` --- - [TCP](https://bun.sh/docs/api/tcp) - `Bun.listen` `Bun.connect` --- - [Transpiler](https://bun.sh/docs/api/transpiler) - `Bun.Transpiler` --- - [Routing](https://bun.sh/docs/api/file-system-router) - `Bun.FileSystemRouter` --- - [HTMLRewriter](https://bun.sh/docs/api/html-rewriter) - `HTMLRewriter` --- - [Utils](https://bun.sh/docs/api/utils) - `Bun.peek` `Bun.which` --- - [SQLite](https://bun.sh/docs/api/sqlite) - `bun:sqlite` --- - [FFI](https://bun.sh/docs/api/ffi) - `bun:ffi` --- - [DNS](https://bun.sh/docs/api/dns) - `bun:dns` --- - [Testing](https://bun.sh/docs/api/test) - `bun:test` --- - [Node-API](https://bun.sh/docs/api/node-api) - `Node-API` --- {% /table %} ## Plugins Support for additional file types can be implemented with plugins. Refer to [Runtime > Plugins](https://bun.sh/docs/bundler/plugins) for full documentation.