Runtime gaps

Known cross-runtime gaps in gossamer’s bindings. Per-binding doc comments flag these inline; this page is the consolidated view.

The minimum runtime versions where gossamer’s test suite passes are visible as badges on the README. Older versions than those are considered unsupported.

Bun

• readable_stream.from_yielder / from_async_yielder — panics via the FFI’s ensureMethod guard. ReadableStream.from is not implemented on Bun. Tracked at oven-sh/bun#3700.
• text_decoder.build / text_decoder_stream.build with legacy single-byte encodings — return Error(UnsupportedEncoding) for 16 encodings Bun’s ICU data omits (iso-8859-2, -4, -5, -10, -13, -14, -15, -16, koi8-r, macintosh, windows-1250, -1251, -1254, -1256, -1258, x-mac-cyrillic). Node and Deno construct them. UTF-8 and both UTF-16 byte orders work everywhere.
• crypto/subtle.derive_bits with length: 0 — resolves with the full shared secret instead of an empty BitArray. Node and Deno resolve with an empty result. Fixed upstream in oven-sh/bun#32819; not yet in a Bun release.
• fetch_extra.response_type — returns ResponseDefault for responses fetched from synthetic sources (e.g. a fetched data: URL) where the Fetch spec, Node, and Deno return ResponseBasic.
• plural_rules.resolved_options — its locale field keeps full input tags like "en-US". Node and Deno normalize the same input to "en". Other Intl formatters (number_format, etc.) keep "en-US" across all three.
• date_time_format.format_to_parts for the Chinese calendar (zh-u-ca-chinese) with year-only options — on macOS, omits the RelatedYear segment that every other runtime/OS pairing emits before YearName (Bun’s JavaScriptCore links the system ICU on macOS and bundles its own on Linux). Option sets that include a month or day emit RelatedYear everywhere.
• date_time_format.format_range — uses regular U+0020 spaces around the en dash. Node and Deno use thin (U+2009) spaces. Assert via substring rather than strict equality if you compare formatted output across runtimes.
• web_socket.info for sockets built from http:/https: URLs — the url field keeps the original scheme where Node and Deno report the normalized ws:/wss: URL.

Deno

• blob.revoke_object_url — Deno throws on unparseable URL strings where the spec, Node, and Bun silently no-op. The FFI catches the throw, so the binding is a silent no-op on every runtime.

Node.js

• abort_signal.timeout(duration) — panics with RangeError: The value of "delay" is out of range for durations longer than 4_294_967_295 ms (~49.7 days, the u32 max). Deno and Bun accept values up to Int’s safe range.

All three runtimes

• plural_rules.select with BigInt — all three runtimes throw TypeError despite the ES2023 spec allowing BigInt inputs. gossamer doesn’t expose the BigInt overload of select; convert via big_int.to_int first when the value fits in Int’s safe range.

Browsers

gossamer’s source targets the current evergreen baseline (Chromium, Firefox, Safari). Browser-specific gaps would be noted here as they’re encountered. CI verifies against Node.js, Deno, and Bun only.

See also

• Conventions — gossamer’s API patterns.
• Coverage — what gossamer wraps.
• Contributing — how gossamer’s FFI handles divergence (Pattern 1: spec default at the FFI boundary; Pattern 2: diagnostic FFI throw).