Web Standards Support

Thunder aims for broad Web Standards compliance. Functions deployed to the runtime can use the same APIs they would use in a modern browser or in Cloudflare Workers, with the obvious exception of DOM and browser-only surfaces.

Compatibility summary

Category	Count	Percentage
Full	62 / 81	77%
Partial	3 / 81	4%
None	16 / 81	20%

Fully supported APIs

The following APIs are available with full spec-level behaviour.

Fetch and networking

API	Notes
`fetch()`	HTTP/1.1 and HTTP/2. Respects egress proxy settings.
`Request`	All standard constructors and methods.
`Response`	Includes `Response.json()`, `Response.redirect()`.
`Headers`	Iterable. Case-insensitive.
`WebSocket`	Client-side `new WebSocket(url)` with per-isolate connection limit.

URL

API	Notes
`URL`	WHATWG URL spec.
`URLSearchParams`	Full iteration and mutation support.
`URLPattern`	Pattern matching for URL routing.

Encoding and serialisation

API	Notes
`TextEncoder`	UTF-8 encoding.
`TextDecoder`	UTF-8, UTF-16, and legacy encodings.
`atob()` / `btoa()`	Base-64 encode and decode.
`structuredClone()`	Deep clone of structured-cloneable values.

Cryptography

API	Notes
`crypto`	Global `crypto.getRandomValues()` and `crypto.randomUUID()`.
`CryptoKey`	Key objects for use with SubtleCrypto.
`SubtleCrypto`	`crypto.subtle` — digest, sign, verify, encrypt, decrypt, key generation.

Streams

API	Notes
`ReadableStream`	Including `ReadableStream.from()` and async iteration.
`WritableStream`	Backpressure-aware writes.
`TransformStream`	Pipeable transform chains.
`CompressionStream`	`gzip`, `deflate`, `deflate-raw`.
`DecompressionStream`	`gzip`, `deflate`, `deflate-raw`.

Binary data and forms

API	Notes
`Blob`	Immutable binary data.
`File`	Extends `Blob` with `name` and `lastModified`.
`FormData`	Multipart form construction and parsing.

Scheduling and lifecycle

API	Notes
`setTimeout()` / `clearTimeout()`	Timer scheduling within wall-clock budget.
`setInterval()` / `clearInterval()`	Repeating timers within wall-clock budget.
`queueMicrotask()`	Microtask queue scheduling.
`AbortController`	Create abort signals.
`AbortSignal`	Signal cancellation of async operations.

Events

API	Notes
`EventTarget`	`addEventListener`, `removeEventListener`, `dispatchEvent`.
`Event`	Base event class.
`CustomEvent`	User-defined event payloads.

Observability and utilities

API	Notes
`console`	`log`, `warn`, `error`, `info`, `debug`, `time`, `timeEnd`, `timeLog`, `trace`, `assert`, `dir`, `table`.
`performance`	`performance.now()` for high-resolution timing.
`Intl`	Full ICU-based internationalisation (number, date, collation, pluralisation).

Partially supported APIs

API	Status	Notes
`navigator`	Partial	`navigator.userAgent` returns the Thunder version string. Other properties are stubs.
`caches`	Partial	Cache API interface is present; behaviour is runtime-scoped, not persisted.
`MessageChannel` / `MessagePort`	Partial	Usable within a single isolate; cross-isolate messaging is not supported.

Not available

The following APIs are not available in the Thunder runtime. Attempting to access them will result in a ReferenceError or a stub that throws.

API	Reason
`document`, `window`, `HTMLElement`, all DOM APIs	No browser rendering engine.
`localStorage` / `sessionStorage`	No persistent client-side storage.
`IndexedDB`	No persistent client-side storage.
`ServiceWorker`	Not applicable to edge function model.
`SharedWorker`	Not applicable to edge function model.
`Worker` (dedicated)	Use isolate-level concurrency instead.
`WebGPU`	No GPU access in edge environment.
`WebRTC`	No peer-to-peer media support.
`WebTransport`	Not yet implemented.
`Notification`	Browser-only API.
`Geolocation`	Browser-only API.
`Bluetooth` / `USB` / `Serial` / `HID`	Hardware APIs not applicable.
`Screen` / `MediaDevices`	Browser-only APIs.

Feature detection

Use standard feature detection when writing portable code:

if (typeof crypto.subtle !== "undefined") {
  // SubtleCrypto is available
}

if (typeof WebSocket !== "undefined") {
  // WebSocket client is available
}

This avoids hard failures when the same bundle is tested in environments with different API surfaces.