Fetch: deviations from the WHATWG standard

This document lists the differences between the RSG runtime and the Fetch Standard. Each difference has an ID, such as F1 for fetch() or H1 for Headers. Items marked SDK are fixable in @roku-sdk; the other items are firmware behavior.

You can reproduce each result by running the fetch-spec-conformance example app.

In the Node.js 24 reference run, 24 of 25 checks pass; only F2 fails (a Roku extension). Streaming, CORS, redirect modes, and referrer policy are untested.

fetch()

The following table lists the differences in the global fetch() function.

ID	Standard	RSG
F1	Invalid `init` rejects with `TypeError`	Rejection fails `instanceof TypeError`
F2	Not part of the standard	`fetch.isFeatureSupported`, `fetch.apiVersion` typed but `undefined` (SDK)

Headers

The following table lists the differences in the Headers class.

ID	Standard	RSG
H1	`new Headers()`	Throws (SDK)
H2	Sequence init	Throws; record init only
H3	Case-insensitive names	Case-sensitive
H4	`append` combines values	Keeps first value
H5	Missing name: `get()` returns `null`	`undefined`
H6	Invalid names throw	Accepted
H7	Values normalized for whitespace	Not normalized
H8	Iterable; `entries`, `forEach`, `getSetCookie`	Missing
H9	`keys()`/`values()`: sorted, lower-cased iterators	Arrays, insertion order

Request

The following table lists the differences in the Request class.

ID	Standard	RSG
RQ1	Body methods, `clone`	Missing
RQ2	`mode`, `credentials`, `cache`, `redirect`, `referrer`, `referrerPolicy`, `integrity`, `keepalive`, `signal`, `duplex`	Missing
RQ3	Relative URLs resolved	Kept as-is
RQ4	Forbidden method throws `TypeError`	Throws `Error`

`Response`

The following table lists the differences in the Response class.

ID	Standard	RSG
RS1	Global `Response`	Missing (SDK)
RS2	`new Response(body, init)`	Does not accept any arguments
RS3	`error`, `json`, `redirect` statics	Missing
RS4	`statusText`, `type`, `redirected`, `body`, `bodyUsed`, `clone`, `formData`	Missing
RS5	`blob()` returns `Blob`	Returns `ArrayBuffer`
RS6	Reused body rejects with `TypeError`	Rejects with `Error`

`AbortController` / `AbortSignal`

The following table lists the differences in the AbortController and AbortSignal classes.

ID	Standard	RSG
A1	Global `AbortController`	Typed, but constructor throws (SDK)
A2	`addEventListener`, `onabort`, `throwIfAborted`	Missing
A3	`abort`, `timeout`, `any` statics	Missing

Missing globals (G1)

The RSG runtime does not define the following globals: ReadableStream, WritableStream, TransformStream, Blob, File, FormData, URL, URLSearchParams, TextDecoder, DOMException, Event, EventTarget, and structuredClone.