Compatibility Matrix

This page documents API compatibility with WHATWG and Node runtime behavior. It also highlights intentional extensions and current native limitations from the Rust wreq layer.

Fetch compatibility

Feature	Status	Notes
`fetch(string \| URL, init)`	Supported	Core entry point.
`fetch(Request, init)`	Supported	Request fields are used unless explicitly overridden by `init`.
Unsupported fetch init fields (`credentials`, `mode`, `cache`, `referrer`, `integrity`, `keepalive`)	Not supported	These fields are currently ignored by `wreq-js` runtime options.
`duplex`	Accepted, no effect	Stream bodies are buffered, which satisfies half-duplex on its own. Accepted so Fetch API code that sets it type-checks.
`Request` class export	Not supported	`Request` can be used as input, but is not exported by this package.
`Response.json/text/arrayBuffer/bytes/clone`	Supported	Includes stream handling and clone semantics.
`Response.blob/formData`	Supported	Implemented through runtime `Response` parsing.
`ReadableStream` and iterable request bodies	Accepted, buffered	Read fully into memory before sending, so an unbounded stream means an unbounded allocation.
Streaming request body uploads	Not supported	The native request bridge expects a buffered body, so bodies are never chunked onto the wire.
Standard timeout behavior	Extended	`wreq-js` defaults to a 30000 ms timeout for safety.
Error type shape	Extended	Errors are `RequestError` which extends `TypeError`.

WebSocket compatibility

Feature	Status	Notes
`websocket(url, options)` helper	Supported	Async helper resolves when open.
`new WebSocket(url, ...)` constructor	Supported	Includes `CONNECTING` state and standard constants.
`onopen/onmessage/onclose/onerror`	Supported	Settable properties with event dispatch ordering by registration time.
`addEventListener/removeEventListener`	Supported	Supports function listeners, object listeners, `once`, and `signal`.
Unknown event names	Supported	Ignored for compatibility with EventTarget behavior.
`send(string \| Buffer \| ArrayBuffer \| ArrayBufferView \| Blob)`	Supported	Blob is converted to bytes before bridge send.
`binaryType="nodebuffer"`	Extension	Node-oriented default for performance and ergonomics.
`binaryType="arraybuffer"`	Supported	Standard compatible binary mode.
`binaryType="blob"`	Supported	Standard compatible binary mode.
`bufferedAmount`	Supported	Best effort byte count based on pending JS side sends.

Session and transport compatibility

Feature	Status	Notes
`createSession` cookie persistence	Supported	Session cookie jar is reused across session requests and session WebSocket connections.
`session.websocket(...)`	Supported	Reuses session transport plus session cookies.
Per request transport override in session fetch	Supported	Use `transport` to override transport details on a specific request.
Per request `browser/os/proxy` inside session websocket	Not supported	Session websocket uses transport from the session context.

Native constraints and roadmap notes

Request upload streaming is currently buffered because the native bridge request API takes full byte payloads.
WebSocket helper remains async by design because connection establishment runs through native upgrade flow.
Additional parity work can be added while preserving current Node-first defaults.