| 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) |
| Clipboard | navigator.clipboard — readText(), writeText(), read(), write(), ClipboardItem, ClipboardEvent (copy/paste fire at navigator.clipboard after its own successful writes/reads). text/plain, text/html, and image/png on every platform. On Linux this requires a $WAYLAND_DISPLAY or $DISPLAY and one of wl-paste/wl-copy, xclip, or xsel (text only). |
| Realms | ShadowRealm |
| Events | EventTarget, Event, ErrorEvent, CloseEvent, MessageEvent |
