Compatibility
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.
| 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) | ✅ |
| 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 |
| Object | Coverage |
|---|
Map | full — including groupBy and live iteration |
Set | full — including intersection, union, difference, symmetricDifference, isSubsetOf, isSupersetOf, isDisjointFrom |
WeakMap, WeakSet, WeakRef, FinalizationRegistry | full |
| Object | Coverage |
|---|
Promise | full — all, race, any, allSettled, withResolvers, async iteration |
AsyncIterator, AsyncGenerator | full |
| Microtask scheduling | ✅ |
| 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) |
| Object | Coverage |
|---|
Proxy | all 13 traps, revocable |
Reflect | all 14 static methods |
| Object | Coverage |
|---|
Error, TypeError, RangeError, ReferenceError, SyntaxError, URIError, EvalError | full |
AggregateError | full |
SuppressedError (Stage 3 explicit resource management) | full |
| 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.) |
| 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) |
| Object | Coverage |
|---|
DisposableStack, AsyncDisposableStack (Stage 3) | full |
Symbol.dispose, Symbol.asyncDispose | full |
using / await using declarations | full |
| 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 | ✅ |
- 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.Tail call optimization — proper tail calls (PTC) are optional in the spec; we don't implement them.
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.
