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)

---

- Web Workers
- [`Worker`](https://developer.mozilla.org/en-US/docs/Web/API/Worker)
  [`self.postMessage`](https://developer.mozilla.org/en-US/docs/Web/API/DedicatedWorkerGlobalScope/postMessage)
  [`structuredClone`](https://developer.mozilla.org/en-US/docs/Web/API/structuredClone)
  [`MessagePort`](https://developer.mozilla.org/en-US/docs/Web/API/MessagePort)
  [`MessageChannel`](https://developer.mozilla.org/en-US/docs/Web/API/MessageChannel)
  [`BroadcastChannel`](https://developer.mozilla.org/en-US/docs/Web/API/BroadcastChannel).

---

- 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)

---

- JSON
- [`JSON`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON)

---

- 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)

<!-- - Blocking. Prints the alert message to terminal and awaits `[ENTER]` before proceeding. -->
<!-- - Blocking. Prints confirmation message and awaits `[y/N]` input from user. Returns `true` if user entered `y` or `Y`, `false` otherwise.
- Blocking. Prints prompt message and awaits user input. Returns the user input as a string. -->

---

- 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 %}