feat(runtime): DOMException and CustomEvent as lazy globals - #452
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DOMException (Web IDL §4.3) arrives as a new lazy builtin: a class grafted onto Error.prototype with branded accessor attributes, the legacy code table, and the constants on interface object and prototype. CustomEvent is defined in events.js next to the Event it extends and placed by the lazy tier through the shared exports cache, so only the placement is deferred — Events::Init now runs the file via GetExports and reads the backing EventTarget from the exports bag. Builtins reach each other through a new internal require tier: registry rows marked internal-only resolve for the require builtins receive and nowhere else, the Node internal-module idiom the js README planned for. The four name-patched-Error stand-ins (abort-signal, performance, structured-clone, base64) now throw real DOMExceptions, required at first throw so the builtin never runs on a clean path, and the native serializer builds the same class for its DataCloneError with the old shape kept as a teardown fallback. With the tier in place the interim internals parameter loses its only two users: kListenerChanged and setListenerErrorReporter move into events.js's exports behind internal/events, and the builtin wrapper drops back to Node's five parameters (exports, require, module, binding, primordials). A consumer that runs before its producer now fails loudly at the require instead of silently reading a missing key. Not implemented: the spec's [Serializable] slot — a DOMException inside a cloned graph still degrades like any custom Error subclass, since v8::ValueSerializer has no hook for a plain JS class. Shared suites (self-gating, skip where the APIs are absent) land in the tests submodule; unguarded canaries on this runtime keep a regression from turning them into silent skips.
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughChangesThe runtime removes the per-isolate Builtin runtime changes
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The submodule update preserves the existing DOMException coverage and adds the CustomEvent suite without introducing an actionable merge-blocking risk; the PR is merge-ready after normal checks. Sequence Diagram(s)sequenceDiagram
participant Runtime
participant BuiltinLoader
participant EventsBuiltin
participant LazyGlobals
participant AbortSignal
Runtime->>BuiltinLoader: Initialize builtin execution
BuiltinLoader->>EventsBuiltin: Load internal/events
EventsBuiltin-->>BuiltinLoader: Export event capabilities
BuiltinLoader-->>LazyGlobals: Return cached CustomEvent export
LazyGlobals-->>Runtime: Publish CustomEvent global
AbortSignal->>BuiltinLoader: require("internal/events")
BuiltinLoader-->>AbortSignal: Return listener-change capability
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Full details: Docstring CoverageExplanation Docstring coverage is 21.21% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 33 functions across 19 files. (6 skipped: 6 unsupported.) ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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edusperoni
marked this pull request as ready for review
August 25, 2026 21:13
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In `@docs/abort-signal.md`:
- Around line 53-55: Update the AbortSignal documentation section covering lines
62-66 to remove the obsolete claim that DOMException is unavailable and abort
reasons are renamed Error instances. Document that AbortSignal.abort() and
AbortSignal.timeout() create DOMException values, including accurate instanceof
DOMException guidance.
In `@NativeScript/runtime/js/events.js`:
- Around line 154-164: Update the CustomEvent constructor’s detail property
definition so it is an own, non-writable property while preserving the existing
detail value and null fallback. Add a canary covering assignment to event.detail
and verify that the original payload remains unchanged.
In `@NativeScript/runtime/js/README.md`:
- Around line 38-41: Update the internal require initialization rule in the
README to state that a cache miss invokes NsBuiltinModules::GetExports and
initializes the registered builtin through BuiltinLoader::GetExports; remove the
incorrect claim that requiring before the producer runs is an
initialization-order failure.
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NativeScript/runtime/BuiltinLoader.cppNativeScript/runtime/BuiltinLoader.hNativeScript/runtime/Events.cppNativeScript/runtime/LazyGlobals.cppNativeScript/runtime/LazyGlobals.hNativeScript/runtime/NsBuiltinModules.cppNativeScript/runtime/NsBuiltinModules.hNativeScript/runtime/StructuredSerialization.cppNativeScript/runtime/StructuredSerialization.hNativeScript/runtime/js/README.mdNativeScript/runtime/js/abort-signal.jsNativeScript/runtime/js/base64.jsNativeScript/runtime/js/dom-exception.jsNativeScript/runtime/js/error-events.jsNativeScript/runtime/js/events.jsNativeScript/runtime/js/performance.jsNativeScript/runtime/js/primordials.jsNativeScript/runtime/js/structured-clone.jsNativeScript/runtime/js/text-encoding.jsTestRunner/app/sharedTestRunner/app/tests/RuntimeImplementedAPIs.jsdocs/abort-signal.mdeslint.config.mjstools/js2c-inputs.xcfilelist
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…racy detail is a readonly attribute in the IDL, unlike the base Event's fields that mutate during dispatch, so define it non-writable. The internal require tier's misdescribed failure mode is corrected in the README and abort-signal comment: a cache miss runs the producer on demand, so a consumer can never observe a missing capability. The docs that still described the pre-DOMException stand-ins (abort-signal, performance, structured-clone, index) now describe the real class.
This was referenced Aug 25, 2026
NathanWalker
approved these changes
Aug 25, 2026
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Follow-up to #448, the next two items of the web-globals plan:
DOMExceptionandCustomEvent, both behind the lazy-global tier.DOMException
New lazy builtin
dom-exception.js(Web IDL §4.3):Error.prototype—instanceof Errorholds andError.prototype.toStringrendersname: message— withname/message/codeas branded, enumerable prototype accessors (private fields double as the Web IDL brand check), the full legacy code table, the 25 constants on interface object and prototype,@@toStringTag, and stack capture.LazyGlobalson first read; until then nothing runs or allocates.Internal require tier
Sibling builtins construct DOMExceptions lazily via a new internal-only specifier tier:
kRegistryrows flaggedinternalOnlyresolve through therequirebuiltins receive and nowhere else (the module system refuses them, and a canary test pins that app code cannot name them). This is the Node internal-module idiom the js README had planned.All five existing stand-in throw sites now produce real DOMExceptions, with the builtin required at first throw so a clean path never runs it:
abort-signal.js— default abort ("AbortError") and timeout ("TimeoutError") reasonsperformance.js— SyntaxError / InvalidModificationError / DataCloneError failuresstructured-clone.js— transfer-list DataCloneErrorbase64.js— atob/btoa InvalidCharacterErrorStructuredSerialization.cpp— the native serializer's DataCloneError, built through the same exports cache (NativeScriptException shape kept as a teardown fallback)internals parameter removed
With the tier in place, the interim
internalsobject had exactly two users left, and both moved intoevents.js's exports behindinternal/events(kListenerChangedfor abort-signal's GC accounting,setListenerErrorReporterfor error-events). The builtin wrapper is back to Node's five parameters (exports, require, module, binding, primordials), and a consumer resolves the capability explicitly at therequire— a cache hit for consumers of eager producers, an on-demand run otherwise — so it can never observe a missing key the way the shared object allowed.CustomEvent
Defined in
events.jsnext to theEventit extends (same ES5 idiom), exported rather than installed:Events::Initnow runs the file throughBuiltinLoader::GetExportsand reads the backing EventTarget from the exports bag, so the lazyCustomEventrow is a cache hit — only the placement is deferred.Not implemented here
The spec's
[Serializable]slot for DOMException — implemented in the stacked follow-up #453 via V8'sIsHostObjectdelegate hook (Node's JSTransferable approach); within this PR alone a DOMException inside a cloned graph still degrades like a custom Error subclass.Tests
DOMExceptionandCustomEventsuites that skip with a visible pending spec where the APIs are absent, plus integration specs — gated per collaborating API — asserting AbortSignal reasons, atob failures and structuredClone failures are real DOMExceptions.RuntimeImplementedAPIs.jsso this runtime regressing the globals fails instead of skipping, plus the app-code-cannot-require-internal pin.Summary by CodeRabbit
DOMExceptionsupport, including legacy error codes and properErrorinheritance.CustomEventsupport with customizable event details.DOMExceptiontypes and names.DataCloneErrorbehavior for unsupported structured-clone operations.DOMExceptionandCustomEventfunctionality.