Parity with txiki.js and Elsa (2026-09-28)

txiki.js and Elsa are small JavaScript runtimes built on QuickJS. This report lists every API they offer and marks, for each one:

whether it belongs to Ecma TC55’s Minimum Common Web API (WinterTC, 2025 snapshot);
its status in Zinc and its Zinc equivalent.

Zinc compiles TypeScript to C++ and has no JS engine, so a few rows cannot apply.

The inventory was taken from the sources:

txiki.js: master @ 8f14257 (2026-09-14). types/src/*.d.ts, src/js/** and website/docs/**.
Elsa: master @ 1982c3d (2022-11-29). js/*.js, core/ops/*.go and cmd/. Elsa is dormant.

Status

exists: in Zinc before this work.
added: added by this work.
partial: available with documented gaps, whether it existed or was added.
missing: not in Zinc.
n/a: needs a JS engine.

The WinterTC column marks the rows of the minimum common API. Those rows came first. In the columns for txiki and Elsa, ✓ means supported, ~ partly, and – absent.

Summary

Rows	exists	added	partial	missing	n/a	total
WinterTC minimum common API	3	21	12	9	0	45
Other Web APIs (txiki / Elsa globals)	0	2	4	7	0	13
`tjs` namespace and Elsa ops	7	29	9	13	2	60
Standard library modules (`tjs:*`, Elsa `std/`)	0	3	4	7	0	14
CLI	5	1	2	3	3	14
All	15	56	31	39	5	146

A row is one line of the tables below. Some lines group several interfaces: the 13 stream classes, the 4 timer functions and the 3 global error hooks are one row each.

Before this work, 15 rows existed in Zinc.
Now, 102 do: 15 existed, 56 were added and 31 are partial. Some partial rows existed before (console, performance, zinc:storage, zinc:events, zinc:net serve).
Not covered: 39 rows are missing and 5 cannot apply.
Of the 45 WinterTC rows, 36 are covered (3 existed, 21 added, 12 partial). The 9 missing ones are:
- streams;
- compression streams;
- the text streams;
- URLPattern;
- the WebAssembly Table, Tag / Exception and streaming functions;
- globalThis / self;
- the global error hooks.

The Zinc side is covered by conformance programs in tests/conformance/: web, fetch_web, fetch, socket, sys_process, fs_ext, os_info, path, sqlite, ffi and wasm. Each one prints the same bytes on the sim and natively (macos; ps1 and esp32 profiles where the capabilities allow). The Web API rows are also checked against Node 24 and against WPT data; see the Web APIs chapter.

1. WinterTC minimum common API

API	txiki	Elsa	WinterTC	Zinc	Zinc equivalent / notes
`AbortController`, `AbortSignal` (`abort`, `timeout`, `any`, `reason`, `throwIfAborted`)	✓	–	✓	added	global (`lib/std/web.ts`)
`Event`	✓	–	✓	added	global; options, phases, `preventDefault` / passive, `composedPath`
`EventTarget`	✓	–	✓	added	global; `once` / `passive` / `signal` / `capture`, exceptions to `reportError`
`CustomEvent`	✓	–	✓	added	global, `CustomEvent<T>` with `{ detail }`
`ErrorEvent`	✓	–	✓	added	global
`MessageChannel`, `MessagePort`	✓	–	✓	partial	global; same thread, no transfer list, no structured clone of the data
`MessageEvent`	✓	–	✓	added	global (`data: unknown`)
`PromiseRejectionEvent`	✓	–	✓	partial	the class exists, but the runtime does not fire `unhandledrejection` (it reports and exits)
`DOMException`	✓	–	✓	added	global, names, legacy `code` and constants
`Headers`	✓	–	✓	added	global (`lib/std/fetch.ts`): validation, sort-and-combine, `getSetCookie`
`Request`	✓	–	✓	added	global; method normalization, body rules, `clone`, body transfer
`Response`	✓	–	✓	partial	global; `error` / `redirect` / `json`; no `body` stream
`FormData`	✓	–	✓	partial	global; multipart serialize, urlencoded parse (no multipart parse)
`Blob`	✓	–	✓	partial	global; `text` / `bytes` / `arrayBuffer` / `slice`; no `stream()`
`File`	✓	–	✓	added	global
`CompressionStream`, `DecompressionStream`	✓	–	✓	missing	needs streams + zlib (≈2 d: miniz as a plugin)
`ReadableStream`, `WritableStream`, `TransformStream` + 10 controller / reader / strategy classes	✓ (polyfill)	–	✓	missing	≈1–2 weeks: a Zinc port of the reference implementation, then `Response.body`, `Blob.stream`, text streams
`TextEncoder`	✓	✓	✓	added	global; `encode`, `encodeInto`
`TextDecoder`	✓	✓	✓	partial	global; UTF-8 only (all its labels), `fatal`, `ignoreBOM`, `stream`; other encodings missing (≈1 d for UTF-16 + windows-1252)
`TextEncoderStream`, `TextDecoderStream`	✓	–	✓	missing	after streams (≈0.5 d)
`URL`	✓	–	✓	added	global; WHATWG parser, WPT urltestdata 896/896, setters 278/278
`URLSearchParams`	✓	–	✓	added	global; `keys()` / `values()` / `entries()` return arrays
`URLPattern`	✓	–	✓	missing	≈3 d (needs a small regex engine: Zinc has no regex)
`Crypto` / `crypto`	✓	–	✓	added	global; `getRandomValues` (OS entropy), `randomUUID`
`SubtleCrypto`	✓ (all)	–	✓	partial	`digest` SHA-1 / 256 / 384 / 512 in Zinc; no keys, sign, encrypt (≈1 week with a vetted C library, e.g. Monocypher + BearSSL)
`CryptoKey`	✓	–	✓	partial	the class only
`Performance` / `performance`	✓	–	✓	partial	`now()` existed; `timeOrigin`, `mark`, `measure` missing (≈0.5 d)
`WebAssembly.Module`, `Instance`	✓ (WAMR)	–	✓	added	`zinc:wasm` on wasm3 (plugin), `WebAssembly` global
`WebAssembly.Memory`	✓	–	✓	partial	exported memory `read` / `write` / `byteLength`; no `grow`, no imported memory
`WebAssembly.Global`	✓	–	✓	partial	read exported globals only
`WebAssembly.Table`	✓	–	✓	missing	≈1 d over wasm3 internals
`WebAssembly.Tag`, `Exception`, `JSTag`	~	–	✓	missing	wasm3 has no exception handling
`WebAssembly.CompileError`, `LinkError`, `RuntimeError`	✓	–	✓	added	from `zinc:wasm`
`WebAssembly.compile`, `instantiate`, `validate`	✓	–	✓	added	`WebAssembly` global
`WebAssembly.compileStreaming`, `instantiateStreaming`	✓	–	✓	missing	after streams; `instantiate(await res.bytes())` works
`atob`, `btoa`	✓	~	✓	added	global, forgiving-base64
`setTimeout` / `clearTimeout` / `setInterval` / `clearInterval`	✓	–	✓	exists	deterministic virtual clock in tests
`queueMicrotask`	✓	–	✓	exists
`console`	✓	~	✓	exists	log / info / debug / warn / error / trace / time / count / assert / table; `group`, `dir`, `countReset` missing
`structuredClone`	✓	–	✓	partial	global; plain data through JSON
`reportError`	–	–	✓	added	global; prints `Uncaught …` and goes on
`navigator.userAgent`	✓	–	✓	added	global `navigator`
`fetch()`	✓	~ (GET text)	✓	added	global; http(s) through libcurl / esp_http_client, `data:`, abort, timeout
`globalThis`, `self`	✓	✓ (`window`)	✓	missing	Zinc rejects `globalThis` (Z1015): no dynamic global object
`onerror`, `onunhandledrejection`, `onrejectionhandled`	✓	–	✓	missing	the runtime reports uncaught errors and exits (crash policy); a hook is ≈1 d

2. Other Web APIs (globals in txiki or Elsa, outside the WinterTC list)

API	txiki	Elsa	Zinc	Zinc equivalent / notes
`WebSocket` client	✓	–	added	`zinc:socket` `WebSocket` (not a global; `ws://` only, no TLS)
WebSocket server (`tjs.serve` websocket)	✓	–	added	`zinc:socket` `serveWebSocket`
`WebSocketStream`	✓	–	missing	after streams
`EventSource`	✓	–	missing	≈0.5 d over fetch once bodies stream
`XMLHttpRequest`	✓	–	missing	legacy; fetch covers it
Direct Sockets `TCPSocket`, `TCPServerSocket`, `UDPSocket`, `PipeSocket`	✓	–	partial	`zinc:socket` (callback API rather than streams)
`TLSSocket`, `TLSServerSocket`	✓	–	missing	needs a TLS library (≈3 d with mbedTLS)
`Worker`, `BroadcastChannel`	✓	–	missing	the runtime has threads natively; a message-passing Worker ≈1 week
`localStorage`	✓	–	partial	`zinc:storage` (`get` / `set` / `remove` / `keys`, persisted; NVS on esp32)
`sessionStorage`	✓	–	missing	a Map does it
`FileReader`	✓	–	missing	legacy; `Blob.text()` / `bytes()`
`encodeURIComponent` / `decodeURIComponent` / `encodeURI` / `decodeURI`	✓	✓	partial	globals from `zinc:web` (ECMAScript, missing from Zinc’s lib before)
`EventEmitter` (Elsa)	–	✓	partial	`zinc:events` `Emitter<T>` (typed, one channel) and `EventTarget`

3. `tjs` namespace and Elsa ops

API	txiki	Elsa	Zinc	Zinc equivalent / notes
`tjs.args`	✓	✓ (`Elsa.args`)	exists	`sys.args()`
`tjs.exePath`	✓	–	missing	≈1 h (`_NSGetExecutablePath` / `/proc/self/exe`)
`tjs.version`, `engine.versions`	✓	–	missing	≈1 h
`tjs.pid`	✓	–	added	`sys.pid()`
`tjs.ppid`	✓	–	missing	≈15 min
`tjs.exit`	✓	–	exists	`sys.exit(code)`
`tjs.cwd`, `tjs.chdir`	✓	✓ (`Elsa.cwd`)	added	`sys.cwd()`, `sys.chdir()`
`tjs.env` (get / set / delete / keys)	✓	✓ (`Elsa.env`)	added	`sys.env`, `setEnv`, `unsetEnv`, `envKeys`
`tjs.hostName`	✓	–	added	`os.hostname()`
`tjs.homeDir`, `tjs.tmpDir`	✓	–	added	`os.homedir()`, `os.tmpdir()` / `fs.tmpdir()`
`tjs.kill(pid, sig)`	✓	–	added	`sys.kill(pid, 'SIGTERM')`
`tjs.addSignalListener`	✓	–	added	`sys.onSignal('SIGTERM', cb)` on the event loop
`tjs.removeSignalListener`	✓	–	missing	≈15 min
`tjs.spawn` with stdin / stdout / stderr pipes	✓	–	exists	`zinc:process` `spawn` / `run` (plugin)
spawn stdio `inherit` / `ignore`, `uid` / `gid`	✓	–	partial	always piped
`Process.wait()` / exit status / term signal, `kill`	✓	–	exists	`p.exited`, `p.code` (128 + signal), `p.kill()`
`tjs.exec` (execvp)	✓	–	missing	≈30 min
`tjs.system.cpus`	✓	–	added	`os.cpus()`, `os.availableParallelism()`
`tjs.system.loadAvg`	✓	–	added	`os.loadavg()`
`tjs.system.uptime`	✓	–	added	`os.uptime()`
`tjs.system.networkInterfaces`	✓	–	added	`os.networkInterfaces()`
`tjs.system.userInfo`	✓	–	added	`os.userInfo()`
memory totals (not in txiki)	–	–	added	`os.totalmem()`, `os.freemem()`, plus `arch`, `type`, `release`
`tjs.stdin`	✓	–	partial	`sys.onStdin(cb)` (chunks); no stream, no raw mode
`tjs.stdout`, `tjs.stderr`	✓	–	added	`sys.write`, `sys.writeErr` (and `console`)
`isTerminal`	✓	–	added	`sys.isatty(fd)`
`setRawMode`, terminal width / height	✓	–	missing	≈0.5 d (termios, TIOCGWINSZ)
`tjs.open` → `FileHandle` (read / write at offsets, truncate, sync, stat)	✓	–	missing	whole-file functions only; ≈1 d
`tjs.readFile`	✓	✓	exists	`fs.readText` / `fs.readBytes` (added)
`tjs.writeFile`	✓	✓	exists	`fs.writeText` / `fs.writeBytes` (added), `appendText`
`tjs.stat`, `tjs.lstat`	✓	✓ (`Elsa.stat`)	added	`fs.stat`, `fs.lstat`
`tjs.statFs`	✓	–	missing	≈30 min
`tjs.readDir`	✓	–	added	`fs.readDir` (with types), `fs.list`
`Elsa.walk`	–	✓	partial	recurse over `fs.readDir`
`tjs.makeDir` (recursive)	✓	✓	added	`fs.mkdir(path, true)`
`tjs.makeTempDir`	✓	–	added	`fs.mkdtemp(prefix)`
`tjs.makeTempFile`	✓	–	missing	≈30 min
`tjs.remove` (recursive)	✓	✓	added	`fs.remove(path, true)`
`tjs.rename`, `tjs.copyFile`	✓	–	added	`fs.rename`, `fs.copyFile`
`tjs.realPath`, `tjs.readLink`, `tjs.symlink`	✓	–	added	`fs.realpath`, `fs.readlink`, `fs.symlink`
`tjs.link`	✓	–	missing	≈15 min
`tjs.chmod`	✓	–	added	`fs.chmod`
`tjs.chown`, `lchown`, `utime`, `lutime`	✓	–	missing	≈1 h
`tjs.watch`	✓	–	added	`fs.watch` / `unwatch` (polling every 100 ms; FSEvents / inotify ≈1 d)
`Elsa.exists`	–	✓	exists	`fs.exists`
`tjs.lookup` (DNS)	✓	–	added	`zinc:socket` `lookup(host)`
`tjs.connect('tcp' \| 'pipe')`	✓	–	added	`zinc:socket` `connect`, `connectUnix`
`tjs.connect('udp')` / `listen('udp')`	✓	–	added	`zinc:socket` `udp()`
`tjs.listen('tcp' \| 'pipe')`	✓	–	added	`zinc:socket` `listen`, `listenUnix`
`tjs.connect('tls')` / `listen('tls')`	✓	–	missing	needs a TLS library (see §2)
`tjs.serve` (fetch-handler HTTP server)	✓	✓ (`Elsa.serve`)	partial	`zinc:net` `serve(port, handler)`: Request / Reply records with headers (added); not `Request` → `Response` objects, no HTTP/2 or TLS
`Elsa.runPlugin` (Go `.so`)	–	✓	partial	native plugins are compiled in (`plugins/`); runtime loading through `zinc:ffi`
`tjs.engine.compile` / `serialize` / `evalBytecode` / `gc`	✓	–	n/a	no JS engine (AOT C++)
`tjs.setImportMap`	✓	–	n/a	modules are resolved at compile time
`tjs.createConsole`	✓	–	missing	≈0.5 d
`tjs.Error` (errno errors)	✓	–	partial	messages start with the errno code (`ENOENT: stat path`)
permissions (`--fs`, `--net`, `--env`)	–	✓	partial	compile-time capabilities (`requires`, Z5003 / Z5005) instead of run-time flags
`Elsa.mode` / tests registry	–	✓	added	`zinc test <dir>` (below)
HTTP/2 / HTTP/3 in fetch	✓	–	partial	libcurl negotiates HTTP/2 over TLS where built with nghttp2
cookie jar, proxy variables	✓	–	partial	libcurl honours `*_proxy`; no cookie jar

4. Standard library modules

Module	txiki	Elsa	Zinc	Zinc equivalent / notes
`tjs:path`	✓	–	added	`zinc:path` (POSIX; the same results as Node’s `path.posix`); no win32 flavour
`tjs:sqlite`	✓	–	added	`zinc:sqlite` plugin, bundled amalgamation 3.53.4
`tjs:ffi`	✓	–	partial	`zinc:ffi` plugin: scalar and string signatures, memory helpers; no structs, callbacks or variadics (≈3 d with libffi)
`tjs:assert`	✓	–	added	`zinc:assert`
`tjs:hashing` (md5 … sha3)	✓	✓ (`std/hash`)	partial	SHA-1 / 256 / 384 / 512 in `zinc:web`; md5, sha224, sha512/t, sha3 and HMAC missing (≈1 d)
`tjs:uuid` (v1–v7)	✓	✓ (`std/uuid`)	partial	v4 via `crypto.randomUUID()`; v7 ≈1 h
`tjs:getopts`	✓	–	missing	≈0.5 d
`tjs:ipaddr`	✓	–	missing	the URL host parser covers IPv4 / IPv6 parsing; CIDR helpers ≈1 d
`tjs:posix-socket`	✓	–	missing	raw sockets, ≈1 d over the socket plugin
`tjs:readline`	✓	–	missing	line editing, history, colours: ≈2 d (needs raw mode)
`tjs:utils` (`inspect`, `format`)	✓	–	partial	`console` formats like Node’s `inspect`, but it is not exposed as a function (≈1 h)
`tjs:wasi`	✓	–	missing	wasm3’s WASI layer as an option of the wasm plugin (≈1 d)
Elsa `std/encoding/hex`, `std/bytes`	–	✓	missing	`toHex` exists in `zinc:web`; the rest ≈0.5 d
Elsa `std/fmt/colors`	–	✓	missing	≈1 h

5. CLI

Command	txiki	Elsa	Zinc	Zinc equivalent / notes
run a program	✓ `tjs run`	✓ `elsa run`	exists	`zinc run` (native or `--target sim`)
type-check	–	✓ `elsa dev`	exists	`zinc check` (TypeScript + Zinc rules)
test runner	✓ `tjs test`	✓ `elsa test`	added	`zinc test <dir>`: every `test-.ts` / `.test.ts`, pass = exit 0, with `zinc:assert`
bundle	✓ `tjs bundle`	✓ `elsa bundle`	n/a	whole-program compilation replaces bundling
standalone executable	✓ `tjs compile`	✓ `elsa pkg`	exists	every `zinc build` is a native executable; `zinc export` packages it with assets
app packages	✓ `tjs app`	–	exists	`zinc export` / `zinc deploy`
`eval` of an expression	✓	–	n/a	no engine; `zinc run` of a file
REPL	✓	✓	missing	a compile-per-line REPL on the sim target is possible (≈3 d); a native REPL needs an interpreter (see `docs/reports` VM design)
`tjs serve FILE`	✓	–	missing	≈0.5 d (a server template calling `zinc:net serve`)
`elsa install` (shims in `~/.elsa`)	–	✓	missing	≈1 h
dev mode	–	✓ `elsa dev`	exists	`zinc dev` (hot reload, red box, inspector)
TypeScript	~ (stripped by esbuild)	~ (esbuild)	partial	Zinc is typed TypeScript, a strict subset: no `eval`, regex or reflection (see chapter 2)
import maps / URL imports	✓	✓	n/a	compile-time module resolution only
`--memory-limit`, `--stack-size`	✓	–	partial	the heap is a fixed budget per profile (`zinc.json` `targets.<id>.heap`)

What remains, with estimates

Ordered by value for server-style programs:

Streams: ReadableStream / WritableStream / TransformStream, then streaming Response.body / Request.body, Blob.stream(), TextEncoderStream / TextDecoderStream and WebSocketStream. About 1–2 weeks. This is the biggest WinterTC gap.
TLS for sockets and wss://, through mbedTLS or the OS (SecureTransport is deprecated). About 3 days, plus certificates on embedded targets.
CompressionStream / DecompressionStream with miniz (MIT). About 2 days after streams.
Web Crypto keys: HMAC, AES-GCM, ECDSA / Ed25519, PBKDF2 / HKDF with a vetted library. About 1 week. HMAC and PBKDF2 alone take about 1 day in Zinc.
Global error hooks: onerror / unhandledrejection events before the crash policy. About 1 day.
FileHandle (positional I/O), statFs, makeTempFile, link, chown, utime. About 1.5 days.
Terminal: raw mode, window size, tjs:readline. About 2.5 days.
Workers with message passing on the existing native threads. About 1 week.
FFI through libffi: structs, callbacks, variadics. About 3 days.
WebAssembly: Table, memory.grow, WASI. About 2 days.
URLPattern, with a small regex engine. About 3 days.
Small items: exePath, version, ppid, exec, removeSignalListener, uuid v7, getopts, colours, serve CLI, console.group / dir. About 2 days in all.

Known compiler limits met on the way

Worked around in the new modules, not fixed:

A generic method called with a lambda does not get its template argument deduced in C++ (db.transaction<T>).
A throwing call inside an array spread or an object literal, in an async function, emits a return; inside a value-returning lambda.
await inside call arguments is evaluated before the earlier arguments.
Zinc classes cannot be iterable ([Symbol.iterator]), so for…of needs entries() arrays.
Rest parameters are refused (Z9009), so path.join takes up to six segments.
Printing an absent string (null / undefined) natively prints an empty string.

Fixed in the compiler and runtime by this work:

?? on nullable strings;
a computed '' being mistaken for null;
integer literals in bitwise operators on the f32 / fx12 profiles;
JSON.stringify calling toJSON;
f64 literals and parameter defaults in the sim under fixed point;
constructor unknown[] contexts;
library any calls in the strict profile;
the event loop exiting while a callback had just started work.

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