Some Web APIs, like the DOM API and History API, aren't relevant in a server-first runtime like Bun. Many others are broadly useful outside the browser; when possible, Bun implements these Web-standard APIs instead of introducing new ones.
Bun partially or completely supports the following Web APIs.
| Category | APIs |
|---|---|
| HTTP | fetch, Response, Request, Headers, AbortController, AbortSignal |
| URLs | URL, URLSearchParams |
| Web Workers | Worker, self.postMessage, structuredClone, MessagePort, MessageChannel, BroadcastChannel |
| Streams | ReadableStream, WritableStream, TransformStream, ByteLengthQueuingStrategy, CountQueuingStrategy and associated classes |
| Blob | Blob |
| WebSockets | WebSocket |
| Encoding and decoding | Uint8Array, Uint8Array.prototype.toBase64(), Uint8Array.fromBase64(), TextEncoder, TextDecoder, atob, btoa |
| JSON | JSON |
| Timeouts | setTimeout, clearTimeout |
| Intervals | setInterval, clearInterval |
| Crypto | crypto, SubtleCrypto, CryptoKey |
| Debugging | console, performance |
| Microtasks | queueMicrotask |
| Errors | reportError |
| User interaction | alert, confirm, prompt (intended for interactive CLIs) |
| Realms | ShadowRealm |
| Events | EventTarget, Event, ErrorEvent, CloseEvent, MessageEvent |