Spec surface

Phasis targets the current ECMAScript specification (ES2024+) and tracks TC39 proposals at Stage 3 and above. This page is the human-readable index of what's actually shipped.

Language

Feature	Status
Lexical declarations (let, const) with TDZ	✅
Block scope, function scope, module scope	✅
Arrow functions (with lexical this)	✅
Default parameters, rest parameters, spread	✅
Destructuring (array, object, nested, defaults, rest)	✅
Template literals, tagged templates	✅
Computed property names	✅
Shorthand properties and methods	✅
Classes — constructors, methods, getters/setters, static	✅
Class fields (public, private, static)	✅
Private methods and accessors	✅
super in methods and constructors	✅
Decorators (Stage 3)	✅
Static initializer blocks	✅
Optional chaining (?.), nullish coalescing (??)	✅
Logical assignment operators (&&=, ||=, ??=)	✅
Numeric separators (1_000_000)	✅
BigInt literals (123n) and operators	✅
Async functions, async generators, top-level await	✅
Generators (sync and async)	✅
for…of, for…in, for await…of	✅
Iterators and iterables (Symbol.iterator)	✅
Symbol primitives and well-known symbols	✅
ES Modules (import / export, dynamic import())	✅
import.meta	✅
import attributes (Stage 3)	✅
Strict mode + Annex B legacy behaviours	✅
Regular expressions (/u, /v, /d, named groups, lookbehind)	✅
Automatic semicolon insertion (ASI)	✅
Hashbang grammar (#!/usr/bin/env phasis)	✅
Proper tail calls in strict mode (ES2015, required by the spec)	✅

Standard library

Fundamental

Object	Coverage
Object	full — keys, values, entries, assign, create, freeze, seal, getOwnPropertyDescriptor(s), setPrototypeOf, getOwnPropertyNames, getOwnPropertySymbols, hasOwn, groupBy, fromEntries, etc.
Array	full — every prototype method including at, flatMap, flat, findLast, findLastIndex, toReversed, toSorted, toSpliced, with, group, groupToMap
String	full — at, codePointAt, match, matchAll, replaceAll, padStart, padEnd, trimStart, trimEnd, isWellFormed, toWellFormed
Number	full — isFinite, isInteger, isNaN, isSafeInteger, EPSILON, MAX_SAFE_INTEGER, etc.
BigInt	full — arbitrary-precision via bcmath
Boolean	full
Math	full — every method, every special-case for NaN / Infinity / -0
JSON	full — parse, stringify, custom replacers, reviver, indentation
Symbol	full — for, keyFor, all well-known symbols, Symbol.toPrimitive
Function	full — call, apply, bind, length, name, prototype semantics

Collections

Object	Coverage
Map	full — including groupBy and live iteration
Set	full — including intersection, union, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom
WeakMap, WeakSet, WeakRef, FinalizationRegistry	full

Async

Object	Coverage
Promise	full — all, race, any, allSettled, withResolvers, async iteration
AsyncIterator, AsyncGenerator	full
Microtask scheduling	✅

Binary data

Object	Coverage
ArrayBuffer, SharedArrayBuffer	full
DataView	full — getBigInt64, setBigInt64, etc.
Int8Array, Uint8Array, Uint8ClampedArray, Int16Array, Uint16Array, Int32Array, Uint32Array, BigInt64Array, BigUint64Array, Float16Array, Float32Array, Float64Array	full
Atomics — add, sub, and, or, xor, compareExchange, exchange, isLockFree, load, notify, pause, store, wait, waitAsync	full (single-agent only)

Reflection and proxies

Object	Coverage
Proxy	all 13 traps, revocable
Reflect	all 14 static methods

Errors

Object	Coverage
Error, TypeError, RangeError, ReferenceError, SyntaxError, URIError, EvalError	full
AggregateError	full
SuppressedError (Stage 3 explicit resource management)	full

Dates and time

Object	Coverage
Date	full
Temporal (Stage 3)	full — Now, Instant, PlainDate, PlainTime, PlainDateTime, PlainYearMonth, PlainMonthDay, ZonedDateTime, Duration, TimeZone, Calendar (incl. Hebrew, Chinese, Dangi, Ethiopic, etc.)

Internationalisation

Object	Coverage
Intl.Locale, Intl.Collator, Intl.DateTimeFormat, Intl.NumberFormat, Intl.PluralRules, Intl.RelativeTimeFormat, Intl.ListFormat, Intl.DisplayNames, Intl.Segmenter	full (delegates to PHP's intl extension when available)

Resource management

Object	Coverage
DisposableStack, AsyncDisposableStack (Stage 3)	full
Symbol.dispose, Symbol.asyncDispose	full
using / await using declarations	full

Other

Object	Coverage
RegExp (incl. /v set notation, named captures, lookaround, sticky/global flags)	full
Iterator helpers (Stage 3) — map, filter, take, drop, flatMap, reduce, toArray, forEach, some, every, find	full
ShadowRealm (Stage 3)	full
globalThis	✅

Web Platform APIs (WHATWG / W3C, not TC39)

Beyond pure ECMAScript, Phasis ships several layered packs of Web APIs that real-world JS libraries pre-check for. See Web APIs for the full surface and per-area conformance.

Pack	Globals	WPT
Web Platform	URL, URLSearchParams, URLPattern, TextEncoder, TextDecoder, atob, btoa, structuredClone, performance, console, setTimeout / setInterval / queueMicrotask, reportError, self (alias of globalThis), DOMException	100 %
Fetch	fetch, Request, Response, Headers, Body mixin, AbortController, AbortSignal, Blob, File, FormData, EventTarget, Event, full WHATWG Streams (ReadableStream, WritableStream, TransformStream, queuing strategies, BYOB), CompressionStream / DecompressionStream (zlib + optional brotli via ext-brotli), navigator	100 %¹
Crypto	crypto.getRandomValues, crypto.randomUUID, full SubtleCrypto (digest, HMAC, AES-GCM/CBC/CTR, RSA-OAEP/PSS/PKCS1, ECDSA P-256/384/521, ECDH, HKDF, PBKDF2)	100 %
WebSocket	WebSocket (constructor + RFC 6455 frame codec, replaceable transport via setWebSocketTransport)	100 %
XHR	XMLHttpRequest + XMLHttpRequestUpload + ProgressEvent (layered over the fetch transport, so policy hooks apply)	100 %
Event loop	setTimeout, setInterval, clearTimeout, clearInterval, queueMicrotask, AsyncContext (Stage 3)	n/a (oracle-tested)

¹ Excluding allowlisted subtests in the compression fixtures: the brotli cases, which need ext-brotli, and the cases that pass SharedArrayBuffer-backed input (EXPECTED_FAILURES in tests/Wpt/WptTest.php).

All other imported Web Platform Tests pass — see Web APIs for the conformance breakdown.

What's not yet implemented

• SharedArrayBuffer worker semantics beyond a single agent — multi-thread atomic notification across real OS threads requires pcntl and isn't on the roadmap. Single-agent atomics work.
• Intl.Segmenter with grapheme clusters that need ICU 76+ — depends on the host PHP's intl extension version.

Versioning

Phasis follows semver. The version line tracks ECMAScript spec drafts:

Phasis version	Spec target	Stage 3 proposals
0.x	ES2024	decorators, Temporal, explicit resource management, iterator helpers, set methods

A bump to 1.0 is gated on every Stage 4 proposal in the ES2025 draft being implemented and on a stable Promise drain semantics.