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JavaScript APIs

Supported JS APIs

Feature Flags

The generated crate supports three feature flags:

FeatureDefaultDescription
logging✅ OnEnables wasi:logging for console API
http✅ OnEnables wasi:http for fetch API
sqlite❌ OffEnables node:sqlite with embedded SQLite

WIT–JS Type Mappings

WIT TypeJS TypeNotes
charstring—
stringstring—
s8, u8, s16, u16, s32, u32number—
s64, u64bigint—
f32, f64number—
option<T>T | undefinedNested options encoded differently
list<T>T[]—
result<T, E>{ tag: "ok", val: T } | { tag: "err", val: E }—
tuple<A, B, C>Array—
enum { a, b, c }"a" | "b" | "c"Matches WIT case names
flags { a, b, c }{ a: boolean, b: boolean, c: boolean }Keys are camelCase
record { .. }ObjectField names are camelCase
variant { .. }{ tag: "x", val: X }val is undefined for unit cases

Mapping Limitations

  • Maximum of 26 function parameters
  • Anonymous interface exports/imports are not supported
  • Imported individual functions into the world are not supported (only whole interfaces)

Available JavaScript APIs

Web Platform APIs

Console

Depends on wasi:logging (if logging feature is enabled), otherwise core WASI.

  • assert, clear, count, countReset, debug, dir, dirXml, error, group, groupCollapsed, groupEnd, info, log, table, time, timeEnd, timeLog, trace, warn

HTTP (fetch)

Requires http feature flag. Depends on wasi:http.

  • fetch, Headers, Request, Response, FormData, Blob, File

URL

  • URL (including createObjectURL, revokeObjectURL)
  • URLSearchParams

Streams

Implemented via web-streams-polyfill .

  • ByteLengthQueuingStrategy, CountQueuingStrategy
  • ReadableStream, ReadableStreamDefaultReader, ReadableStreamBYOBReader, ReadableStreamDefaultController, ReadableByteStreamController, ReadableStreamBYOBRequest
  • WritableStream, WritableStreamDefaultController
  • TransformStream, TransformStreamDefaultController

Timers

  • setTimeout, clearTimeout, setInterval, clearInterval, setImmediate

Abort Controller

  • AbortController, AbortSignal, DOMException

Encoding

  • TextEncoder, TextDecoder, TextDecoderStream, TextEncoderStream

Messaging

  • MessageChannel, MessagePort

Events

  • Event, EventTarget, CustomEvent

Intl (Internationalization)

Minimal en-US implementation — all locale inputs are accepted but resolved to en-US. When the timezone feature is enabled (default), DateTimeFormat supports all ~590 IANA timezones via chrono-tz.

  • Intl.DateTimeFormat — format(), formatToParts(), resolvedOptions(), supportedLocalesOf()
  • Intl.NumberFormat — format(), formatToParts(), resolvedOptions(), supportedLocalesOf()
  • Intl.Collator — compare(), resolvedOptions(), supportedLocalesOf()
  • Intl.PluralRules — select(), selectRange(), resolvedOptions(), supportedLocalesOf()
  • Intl.getCanonicalLocales(), Intl.supportedValuesOf()

Crypto (global)

  • crypto.randomUUID, crypto.getRandomValues

Structured Clone

Via ungap/structured-clone :

  • structuredClone

Node.js-Compatible Modules

node:assert

  • ok, equal, notEqual, strictEqual, notStrictEqual
  • deepEqual, notDeepEqual, deepStrictEqual, notDeepStrictEqual, partialDeepStrictEqual
  • throws, doesNotThrow, rejects, doesNotReject
  • ifError, match, doesNotMatch, fail
  • AssertionError, CallTracker
  • strict — strict mode variant

node:async_hooks

  • AsyncLocalStorage — run, exit, getStore, enterWith, disable, snapshot, bind
  • AsyncResource — runInAsyncScope, asyncId, triggerAsyncId, bind
  • createHook — stub (returns enable/disable no-ops)
  • executionAsyncId, triggerAsyncId, executionAsyncResource — stubs

⚠️ Limitation: Context is not propagated across await boundaries (QuickJS internal behavior).

node:buffer

  • Buffer, Blob, File, SlowBuffer
  • resolveObjectURL, isAscii, isUtf8
  • INSPECT_MAX_BYTES, kMaxLength, kStringMaxLength, constants

node:child_process (stub)

All spawn/exec functions throw ENOSYS — WASI does not support process creation.

  • ChildProcess, exec, execFile, fork, spawn, execSync, execFileSync, spawnSync

node:cluster (stub)

Clustering not supported in WASM.

  • isPrimary, isMaster, isWorker, fork, disconnect, setupPrimary

node:constants

Merged constants from os.constants, fs.constants, and crypto.constants (signal numbers, errno values, file flags, etc.)

node:crypto

  • Hashing: createHash, createHmac, hash, getHashes
  • Ciphers: createCipheriv, createDecipheriv, getCiphers
    • Supported ciphers: aes-128/256-cbc, aes-128/256-ctr, aes-128/256-gcm, aes-128/192/256-wrap, id-aes128/192/256-wrap, id-aes128/192/256-wrap-pad, des-ede3-cbc, des3-wrap, chacha20-poly1305
  • Signing: createSign, createVerify (Ed25519, ECDSA with P-256, P-384, secp256k1)
  • Keys: createPublicKey, createPrivateKey, createSecretKey, KeyObject, generateKeyPairSync, generateKeyPair
  • ECDH: createECDH, ECDH, diffieHellman, getCurves
  • Certificate: Certificate (verifySpkac, exportPublicKey, exportChallenge)
  • Random: randomBytes, randomFillSync, randomFill, randomInt, randomUUID, pseudoRandomBytes, prng, rng
  • KDF: pbkdf2, pbkdf2Sync, scrypt, scryptSync, hkdf, hkdfSync
  • Primes: generatePrime, generatePrimeSync, checkPrime, checkPrimeSync
  • Other: timingSafeEqual, getFips, setFips, secureHeapUsed

node:dgram

UDP datagram sockets built on WASI sockets.

  • dgram.createSocket(type[, listener]) — udp4 or udp6
  • socket.bind, socket.send, socket.sendto, socket.connect, socket.disconnect, socket.close
  • socket.address(), socket.remoteAddress()
  • socket.setTTL, socket.setRecvBufferSize/getRecvBufferSize, socket.setSendBufferSize/getSendBufferSize
  • socket.ref()/socket.unref() — no-op
  • Events: message, listening, close, error, connect

⚠️ Multicast operations throw ENOSYS.

node:diagnostics_channel

  • channel, subscribe, unsubscribe, hasSubscribers, tracingChannel
  • Channel — subscribe, unsubscribe, publish, bindStore, unbindStore, runStores, hasSubscribers, name
  • TracingChannel — subscribe, unsubscribe, hasSubscribers, traceSync, tracePromise, traceCallback
  • Built-in HTTP diagnostics channels: http.client.request.created, http.client.request.start, http.client.request.error, http.client.response.finish

node:dns

DNS resolution via WASI sockets.

  • lookup, lookupService, resolve, resolve4, resolve6
  • resolveAny, resolveCname, resolveCaa, resolveMx, resolveNaptr, resolveNs, resolvePtr, resolveSoa, resolveSrv, resolveTxt, resolveTlsa
  • reverse, setServers, getServers, setDefaultResultOrder, getDefaultResultOrder
  • Resolver class
  • promises — promise-based API
  • Error constants: NODATA, FORMERR, SERVFAIL, NOTFOUND, NOTIMP, REFUSED, BADQUERY, BADNAME, BADFAMILY, BADRESP, CONNREFUSED, TIMEOUT, EOF, FILE, NOMEM, DESTRUCTION, BADSTR, BADFLAGS, NONAME, BADHINTS, NOTINITIALIZED, LOADIPHLPAPI, ADDRGETNETWORKPARAMS, CANCELLED, ADDRCONFIG, V4MAPPED, ALL

node:domain

Deprecated sync-only error-handling domains.

  • domain.create()/domain.createDomain(), domain.active, domain._stack
  • Domain class (extends EventEmitter): run, add, remove, bind, intercept, enter, exit, dispose, members, parent
  • process.domain — reflects active domain
  • Error decoration: error.domain, error.domainEmitter, error.domainBound, error.domainThrown

⚠️ No async context propagation via async_hooks.

node:events

  • EventEmitter — on, once, off, addListener, removeListener, removeAllListeners, emit, listenerCount, eventNames, listeners, rawListeners, prependListener, prependOnceListener, setMaxListeners, getMaxListeners
  • Static: once, on, getEventListeners, getMaxListeners, setMaxListeners, addAbortListener, errorMonitor, captureRejections
  • Event, EventTarget, CustomEvent

node:fs

Comprehensive filesystem API on WASI filesystem.

  • Sync: readFileSync, writeFileSync, appendFileSync, openSync, closeSync, readSync, writeSync, ftruncateSync, fsyncSync, fdatasyncSync, statSync, lstatSync, fstatSync, statfsSync, readdirSync, accessSync, existsSync, realpathSync, truncateSync, copyFileSync, linkSync, symlinkSync, readlinkSync, chmodSync, fchmodSync, lchmodSync, chownSync, fchownSync, lchownSync, utimesSync, futimesSync, lutimesSync, unlinkSync, renameSync, mkdirSync, rmdirSync, rmSync, mkdtempSync, opendirSync, readvSync, writevSync, cpSync
  • Async (callback): readFile, writeFile, appendFile, open, close, read, write, stat, lstat, fstat, statfs, ftruncate, fsync, fdatasync, readdir, access, exists, realpath, truncate, copyFile, link, symlink, readlink, chmod, fchmod, lchmod, chown, fchown, lchown, utimes, futimes, lutimes, unlink, rename, mkdir, rmdir, rm, mkdtemp, opendir, watch, watchFile, unwatchFile, readv, writev, cp, openAsBlob
  • Streams: createReadStream, createWriteStream
  • Classes: Stats, Dirent, Dir, FSWatcher, StatWatcher, ReadStream, WriteStream
  • Constants: F_OK, R_OK, W_OK, X_OK, O_RDONLY, O_WRONLY, O_RDWR, O_CREAT, O_EXCL, O_TRUNC, O_APPEND, and more

node:fs/promises

  • FileHandle, open, readFile, writeFile, appendFile, unlink, rename, mkdir, rmdir, rm, stat, lstat, readdir, opendir, access, realpath, truncate, copyFile, link, symlink, readlink, chmod, lchmod, chown, lchown, utimes, lutimes, mkdtemp, cp, watch, statfs, constants

node:http / node:https

Requires http feature flag. Client uses wasi:http (TLS transparent). Server uses wasi:sockets for TCP-level HTTP/1.1.

  • http.request, http.get, http.METHODS, http.STATUS_CODES, http.maxHeaderSize, http.validateHeaderName, http.validateHeaderValue
  • http.Agent, http.globalAgent
  • http.OutgoingMessage, http.ClientRequest, http.IncomingMessage
  • https.request, https.get
  • http.createServer, http.Server, http.ServerResponse
  • Server-side IncomingMessage with method, url, headers, rawHeaders, httpVersion, socket, etc.
  • node:_http_common — _checkIsHttpToken, _checkInvalidHeaderChar
  • Supports: keep-alive, chunked transfer encoding, content-length bodies, sequential pipelining, idle connection cleanup

⚠️ Not yet supported: HTTP Upgrade, 1xx events, server-side timeout enforcement, https.createServer().

node:http2 (stub)

  • connect, createServer, createSecureServer, Http2ServerRequest, Http2ServerResponse

node:inspector (stub)

No V8 inspector in WASM.

  • Session, open, close, url, waitForDebugger, console, Network

node:module

  • require, createRequire, builtinModules, isBuiltin, runMain, _nodeModulePaths

node:net

TCP sockets and servers on WASI sockets.

  • net.createServer, net.createConnection, net.connect
  • net.isIP, net.isIPv4, net.isIPv6
  • net.getDefaultAutoSelectFamily/net.setDefaultAutoSelectFamily — stubs
  • net.Socket (extends stream.Duplex): connect, write, end, destroy, resetAndDestroy, setTimeout, setNoDelay, setKeepAlive, address, ref, unref; properties: remoteAddress, remotePort, remoteFamily, localAddress, localPort, localFamily, bytesRead, bytesWritten, connecting, pending, readyState; events: connect, ready, data, end, close, error, timeout, drain, lookup
  • net.Server (extends EventEmitter): listen, close, address, getConnections, ref, unref; properties: listening, maxConnections; events: listening, connection, close, error, drop
  • net.BlockList, net.SocketAddress, net.Stream

⚠️ Not supported: IPC/Unix domain sockets, cluster integration.

node:os

  • arch, platform, type, release, version, machine, hostname, homedir, tmpdir, endianness
  • cpus, loadavg, freemem, totalmem, uptime, availableParallelism
  • networkInterfaces, userInfo, getPriority, setPriority
  • EOL, devNull, constants

node:path

  • sep, delimiter, basename, dirname, extname, isAbsolute, join, normalize, relative, resolve, parse, format, matchesGlob, toNamespacedPath, posix

node:perf_hooks

  • performance — now(), timeOrigin, mark(), measure(), getEntries(), getEntriesByName(), getEntriesByType(), clearMarks(), clearMeasures(), toJSON()
  • PerformanceEntry, PerformanceObserver
  • monitorEventLoopDelay, createHistogram, constants

node:process

  • Properties: argv, argv0, env, pid, ppid, platform ('wasi'), arch ('wasm32'), version, versions, config, features, execArgv, execPath, exitCode, stdout, stderr
  • Methods: exit, cwd, nextTick, hrtime, hrtime.bigint, uptime, cpuUsage, memoryUsage, kill, abort, emitWarning
  • User/Group: getuid, getgid, geteuid, getegid, getgroups, setuid, setgid
  • Extends EventEmitter — supports on('uncaughtException'), on('unhandledRejection'), etc.

node:punycode

  • decode, encode, toASCII, toUnicode, ucs2, version

node:querystring

  • stringify/encode, parse/decode, escape, unescape, unescapeBuffer

node:readline

  • createInterface, Interface, clearLine, clearScreenDown, cursorTo, moveCursor, emitKeypressEvents
  • readline/promises — promise-based API

node:repl (stub)

  • start, REPLServer, Recoverable, builtinModules

node:sqlite

Requires sqlite feature flag. Synchronous API with embedded SQLite engine.

  • DatabaseSync — prepare, exec, close, open, isOpen, isTransaction, createSession, applyChangeset, enableLoadExtension, function, aggregate, backup
  • StatementSync — run, get, all, iterate, columns, setReadBigInts, setAllowBareNamedParameters, sourceSQL, expandedSQL
  • Session — changeset, patchset, close
  • Constants: SQLITE_CHANGESET_OMIT, SQLITE_CHANGESET_REPLACE, SQLITE_CHANGESET_ABORT

⚠️ loadExtension() throws — native extensions cannot be loaded in WASM.

node:stream

  • Readable (with from, fromWeb, toWeb, wrap, map, filter, flatMap, take, drop, toArray, forEach, reduce, some, every, find)
  • Writable, Duplex, Transform, PassThrough, Stream
  • pipeline, finished, compose, duplexPair, addAbortSignal
  • getDefaultHighWaterMark, setDefaultHighWaterMark, isDisturbed, destroy
  • stream/consumers — arrayBuffer, blob, buffer, json, text
  • stream/promises — promise-based pipeline and finished

node:string_decoder

  • StringDecoder

node:test

Built-in test runner.

  • test, describe/suite, it, before, after, beforeEach, afterEach
  • mock — function mocking
  • run — programmatic test execution

node:timers

  • setTimeout, setInterval, setImmediate, clearTimeout, clearInterval
  • timers/promises — promise-based setTimeout, setInterval, setImmediate

node:tls (stub)

TLS is handled transparently by the WASI-HTTP layer.

  • SecureContext, TLSSocket, Server, connect, createServer, createSecureContext, checkServerIdentity, getCiphers, rootCertificates
  • DEFAULT_MIN_VERSION, DEFAULT_MAX_VERSION, DEFAULT_ECDH_CURVE

node:trace_events

  • createTracing({ categories }) — creates a Tracing handle
  • Tracing#enable()/Tracing#disable(), Tracing#enabled, Tracing#categories
  • getEnabledCategories()

⚠️ No native trace sink — API-surface compatibility only.

node:tty

  • isatty, ReadStream, WriteStream

node:url

  • URL, URLSearchParams
  • parse, resolve, format (legacy)
  • fileURLToPath, pathToFileURL, urlToHttpOptions

node:util

  • format, inspect, deprecate, debugLog, log
  • Type checks: isArray, isBoolean, isNull, isNullOrUndefined, isNumber, isString, isSymbol, isUndefined, isRegExp, isObject, isDate, isError, isFunction, isPrimitive, isBuffer
  • promisify, callbackify
  • parseEnv, styleText, getCallSite, getCallSites, toUSVString, _extend
  • TextEncoder, TextDecoder

node:v8

  • getHeapStatistics, getHeapSpaceStatistics, getHeapSnapshot, getHeapCodeStatistics
  • setFlagsFromString, writeHeapSnapshot, takeCoverage, stopCoverage
  • serialize, deserialize, Serializer, Deserializer, DefaultSerializer, DefaultDeserializer

node:vm

  • runInNewContext, runInContext, runInThisContext, createContext, isContext, compileFunction
  • Script, createScript
  • SourceTextModule (experimental — limited export const/export let/export var support)

node:worker_threads (stub)

Workers not supported in single-threaded WASM.

  • isMainThread, parentPort, workerData, threadId, resourceLimits
  • Worker, BroadcastChannel, MessagePort, MessageChannel
  • markAsUntransferable, moveMessagePortToContext, receiveMessageOnPort
  • getEnvironmentData, setEnvironmentData

node:zlib

  • Classes: Deflate, Inflate, Gzip, Gunzip, DeflateRaw, InflateRaw, Unzip, BrotliCompress, BrotliDecompress
  • Factory: createGzip, createGunzip, createDeflate, createInflate, createDeflateRaw, createInflateRaw, createUnzip, createBrotliCompress, createBrotliDecompress
  • Async: gzip, gunzip, deflate, inflate, deflateRaw, inflateRaw, unzip, brotliCompress, brotliDecompress
  • Sync: gzipSync, gunzipSync, deflateSync, inflateSync, deflateRawSync, inflateRawSync, unzipSync, brotliCompressSync, brotliDecompressSync
  • crc32, constants, codes

Internal / Compatibility Modules

  • internal/url — isURL
  • internal/http — kOutHeaders symbol
  • base64-js — byteLength, toByteArray, fromByteArray
  • ieee754 — read, write

Built-in Language Features (from QuickJS)

These come from QuickJS itself and are available globally without any import:

Globals: parseInt, parseFloat, isNaN, isFinite, quickMicrotask, decodeURI, decodeURIComponent, encodeURI, encodeURIComponent, escape, unescape, Infinity, NaN, undefined

Full built-in objects with all standard methods: Object, Function, Error, Generator, Iterator, Array, Number, Boolean, String, Symbol, Map, Set, WeakMap, WeakSet, GeneratorFunction, Math, Reflect, RegExp, JSON, Promise, AsyncFunction, AsyncIterator, AsyncGeneratorFunction, AsyncGenerator, Date, BigInt, ArrayBuffer, SharedArrayBuffer

Typed Arrays: Int8Array, Uint8Array, Int16Array, Uint16Array, Int32Array, Uint32Array, BigInt64Array, BigUint64Array, Float32Array, Float64Array, Float16Array

Other: DataView, Atomics, Performance, WeakRef, FinalizationRegistry, Callsite, Proxy

Additional Resources

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