ES feature matrix

Status vocabulary: Status vocabulary. Edition pin: ECMAScript 2026 (17th edition) — Sources · HTML 17.0.
Oracle: Test262 (in-scope).
Update rule: change status only with tests + PR. Do not claim a newer edition without re-pin.

Rows start honest for a greenfield engine. partial reflects early scripty smokes where applicable.

Syntax & language

Feature	Status	Notes / tests
Lexer / tokenizer	`partial`	`src/syntax/lexer.zig`
Parser (statements / expressions)	`partial`	`src/syntax/parser.zig`
Strict mode	`partial`	Default/strict edge cases incomplete
Classes (methods, heritage, static)	`unsupported`	—
Private fields / methods / accessors	`unsupported`	—
`async` / `await`	`partial`	Promises exist; full async fn semantics TBD
Generators / `yield`	`unsupported`	—
Async generators	`unsupported`	—
Arrow functions	`partial`	Smoke coverage only
Destructuring	`partial`	Incomplete
Rest / spread	`partial`	Incomplete
Default parameters	`partial`	Incomplete
Optional chaining `?.`	`unsupported`	—
Nullish coalescing `??`	`unsupported`	—
Logical assignment `&&=` `\|\|=` `??=`	`unsupported`	—
Numeric separators	`unsupported`	—
BigInt literals	`unsupported`	—
Template literals (incl. tagged)	`partial`	Incomplete
`for-of` / `for-await-of`	`unsupported`	—
`using` / explicit resource management	`unsupported`	In-scope: reached Stage 4 and is in ES2026 (ECMA-262 17th ed.)

Types & values

Feature	Status	Notes / tests
undefined / null / boolean / number / string	`partial`	`src/vm/values.zig`
Object / Array	`partial`	Simple property model
Function	`partial`	Host + JS functions
Symbol	`unsupported`	—
BigInt	`unsupported`	—
Property attributes	`partial`	Not full descriptor model
Prototypes	`partial`	—
Exotic objects path	`unsupported`	—

Execution & runtime semantics

Feature	Status	Notes / tests
Bytecode + interpreter	`partial`	`src/vm/*`
Lexical environments	`partial`	—
`this` binding	`partial`	—
`new` / constructors	`partial`	—
try / catch / finally	`partial`	—
Exceptions / `Error` throw	`partial`	—
Promises + jobs	`supported`	`testdata/smoke/promise_then.js`, microtask order
Microtask ordering vs timers	`supported`	`testdata/smoke/microtask_order.js`

Built-in groups (summary)

Detail: Built-ins.

Group	Status	Notes
Object / Function / Array basics	`partial`	—
String / Number / Boolean / Math	`partial` / `unsupported`	Math largely missing
Date / JSON / Error	`unsupported` / `partial`	—
Promise (built-in surface)	`partial`	then/jobs; not full static API
Symbol / Map / Set / Weak*	`unsupported`	—
RegExp	`unsupported`	—
TypedArray / ArrayBuffer / DataView	`unsupported`	—
Proxy / Reflect	`unsupported`	—
Iterator helpers (ES2025+)	`unsupported`	—
Set methods (ES2025+)	`unsupported`	—
Intl	`unsupported`	Scope decision: implement or refuse

Modules (language)

Feature	Status	Notes / tests
ESM parse / link / evaluate (local)	`partial`	Relative only; smokes
Cyclic modules	`unsupported`	—
Top-level await	`unsupported`	—
Import attributes	`unsupported`	As required by pin
`import.meta`	`partial`	Minimal / host-dependent

GC

Feature	Status	Notes
Precise STW mark–sweep + freelist	`partial`	Design in repo `docs/vm-gc.md`; auto collect exists
Incremental GC	`unsupported`	Post language-gate OK

Annex B (opt-in)

Feature	Status	Policy
Annex B syntax/semantics (aggregate)	`unsupported`	Opt-in per concrete row when added

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All in-scope rows above (and their detailed built-in rows) must be supported or dogfooded, with Test262 blockers at zero. See Scope.

Get started

v0.0.1-dev program

I1 — ES Engine

I2 — Bun-exclusive

I3 — Deno-exclusive

Reference

ES feature matrix

ES feature matrix

Syntax & language

Types & values

Execution & runtime semantics

Built-in groups (summary)

Modules (language)

GC

Annex B (opt-in)

Exit bar for I1

​ES feature matrix

​Syntax & language

​Types & values

​Execution & runtime semantics

​Built-in groups (summary)

​Modules (language)

​GC

​Annex B (opt-in)

​Exit bar for I1

ES feature matrix

Syntax & language

Types & values

Execution & runtime semantics

Built-in groups (summary)

Modules (language)

GC

Annex B (opt-in)

Exit bar for I1