# 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](/docs/compatibility/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](/docs/compatibility/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.