Add three foundational ES2015 features to the JS engine:
- Symbol: unique identity values, well-known symbols (iterator, toPrimitive,
hasInstance, toStringTag, species, isConcatSpreadable), Symbol.for/keyFor
registry, symbol-keyed properties, coercion guards, and computed member
access support.
- WeakMap: object-keyed map with get/set/has/delete, TypeError for
non-object keys, and proper prototype chain setup.
- Proxy: get/set/has/deleteProperty/ownKeys/apply/construct traps,
Proxy.revocable with internal revoke slot, and function proxy support.
Also fixes 14 code review issues including: template literal Symbol TypeError
propagation, abstract equality for symbols, comparison/arithmetic TypeError
guards, delete on symbol-keyed properties, Symbol.iterator support in
destructuring and for-of, and replacement of __proxy__/__target_fn__ sentinel
properties with proper internal slots.
Box JsFunction inside JsValue enum to reduce enum size from ~200 to ~48 bytes,
fixing stack overflow in deep recursion tests caused by accumulated frame bloat.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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