[cramforce]

An EventEmitter used both through its static type and through an untyped reference aborted the process. A typed on followed by an untyped emit of the same event, or a typed emit from a class body reaching a listener added through any (the shape of function-local class expressions whose instances escape untyped), hit scr_trap("scriptc: computed event collided with a fixed event"), and an untyped emit('error', ...) trapped unconditionally.

Root cause: a listener entry held either a typed adapter (called with the emit site's fixed tuple as C variadics) or a checked-dynamic thunk (called with the untyped argument vector), and the emit core trapped when an entry lacked the form the emit carried.

Runtime (scr_events_emitter.c):

• An entry may carry both forms. scr_emitter_on_dyn keeps the listener's thunk beside its typed adapter, so typed emits call the adapter and untyped emits call the thunk with the arguments as given (extra arguments included).
• scr_emitter_emit_mixed carries both the untyped arguments and a compiler-converted typed tuple, for untyped emits of an event that has listeners with typed parameters. scr_emitter_has_typed says whether the conversion is needed.
• scr_emitter_on_any / scr_emitter_emit_any serve registrations and emits through untyped values: runtime-built typed adapters under error and the meta events; emit('error') emits to errorMonitor first, then to listeners, and with none throws an Error payload itself and primitive payloads as ERR_UNHANDLED_ERROR. Untyped newListener/removeListener listeners receive the listener function when it was registered through an untyped value.
• The emit core throws a catchable error instead of trapping when an entry has no usable form.
• The meta-event argument vectors and rebuilt listener values sit behind a hook that only scr_emitter_on_any installs, and scr_emitter_on_flex/emit_flex keep their plain behavior for computed names and the worker registries, so programs without untyped emitter calls link none of the new dynamic code.

Compiler:

• The class dispatch of compiled emitters (non-stream) routes untyped on/once/prepend* under an event typed code emits or listens to with typed parameters through emitter.onDyn with a typed adapter for the event's tuple, and untyped emit of such an event converts its arguments to the tuple (a mismatch throws the checked conversion's TypeError) when hasTyped says a typed listener is registered. These helpers exist only in programs that have such events and untyped emitter calls.
• listenerCount, eventNames, removeAllListeners, listeners, rawListeners, setMaxListeners and getMaxListeners called through an untyped value on a compiled emitter (a program class extending EventEmitter, or new EventEmitter()) answered "is not a function"; they now dispatch to the native registry with Node's results. In TypeScript the last four names join the dyn-dispatch method set so such calls lower to a dispatch.

Explicit refusals remain for what is not modeled, documented on the EventEmitter limitations page: listeners() through an untyped value of an event with a typed listener, untyped emit('error') of a non-Error object with no listener, untyped emits whose arguments do not convert to a typed listener's tuple (TypeError before any listener runs), and typed listener functions as the second meta-event argument (undefined).

Scope: under the scope-B plan, this PR keeps only the typed/untyped listener sharing and the catchable throw in place of the trap. The follow-up that answered EventEmitter methods read as values (o.on, EventEmitter.prototype.on in JavaScript, constructor-function emitters, dyn.emitterMethod, corpus 6600–6602) was reverted in 3f3e90b, because those forms belong to Node islands. Reading EventEmitter methods as properties through an untyped value still answers undefined, as the limitations page says. main (0237d70) is merged in.

Evidence (Linux sandbox, final branch against main 0237d70, both trees built with their own runtime pack):

• Corpus 6580–6584 pin the behavior against Node in the plain and sanitized lanes. Differential -t "658[0-4]|emitter" 18 passed, sanitized 6 passed, -t "event|5137|6469|648[0-2]|6494|cjs-class-hierarchy" 56 passed.
• packages/runtime/test and packages/compiler/src/ir: 492 passed, 1 failed (bigint runtime builds for wasm32, the known wasm32-wasi environment failure in the sandbox).
• pnpm lint, pnpm format:check, pnpm test:ts7 --baselines-only pass; the self-hosted --emit=ir build of packages/compiler/src/native/cli.ts reports no diagnostics.
• Zero-cost gate (scripts/zero-cost-gate.mjs, bench, self and TypeScript corpus, 2718 programs): 2502 identical, 216 differ. The self-hosted compiler is identical. 209 differ only in the executable, because the emitter runtime unit they link changed (scr_ee_add in 207, scr_ee_emit_core in 6; growth +0.01% to +3.3%). Six bench workloads are among them (channel-messages, atomics-contended, intern-table, thread-slots, typed-array-scan-workers, worker-messages: +120 to +128 B each); their IR and LLVM are identical. 7 differ in IR/LLVM: 6469, 6480, 6481, 6482, 6494 and cjs-class-hierarchy-npm make untyped calls on compiled emitters, and their class dispatch now calls the new entry points (the intended change); fs-extra-package differs only by the shim's absolute checkout path. Compile time: bench geomean -0.27% [95% CI -1.71%, +0.96%], self-hosted -1.6%, both within tolerance.
• Earlier, on 139542b: a typed emit loop (20M emits to three listeners, plus periodic on/off), 21 interleaved runs: median 928 ms vs 899 ms (no slowdown; the difference is layout noise).

Overlap: #1544 (opt/ee-class-value-crash) also touches EventEmitter handling through untyped values (builtin-class-dyn.ts, relational.ts, lowerer.ts, lower-classes.ts); this change touches none of those files.

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Project	Deployment	Actions	Updated
scriptc	Ready	Preview, v0	Oct 21, 2026 3:44pm UTC