EventEmitter.prototype methods (emit/on/…) are undefined — breaks the setPrototypeOf mixin pattern (pino)

[proggeramlug]

Summary

EventEmitter.prototype.emit (and .on, .once, etc.) resolve to undefined, even though EventEmitter instances dispatch those methods fine. So the common "mixin EventEmitter into a prototype" pattern — Object.setPrototypeOf(myProto, EventEmitter.prototype) — produces objects with no emit.

This breaks pino (one of the most-used npm loggers): lib/proto.js:77 does Object.setPrototypeOf(prototype, EventEmitter.prototype), then lib/levels.js:98 calls this.emit('level-change', …) → TypeError: emit is not a function (located via --debug-symbols).

Minimal reproduction

import { EventEmitter } from "node:events"

console.log("EE.prototype.emit:", typeof (EventEmitter.prototype as any).emit)  // undefined  (Node: function)
console.log("EE.prototype.on:",   typeof (EventEmitter.prototype as any).on)    // undefined  (Node: function)

const e: any = new EventEmitter()
console.log("instance.emit:", typeof e.emit)                                     // function  ✅ (instances work)
console.log("getProto(instance) === EE.prototype:", Object.getPrototypeOf(e) === EventEmitter.prototype) // true
console.log("getProto(instance).emit:", typeof Object.getPrototypeOf(e).emit)    // undefined ❌

// the pino mixin shape:
const proto: any = { foo() {} }
Object.setPrototypeOf(proto, EventEmitter.prototype)
const inst: any = Object.create(proto)
console.log("mixin inst.emit:", typeof inst.emit)                                // undefined ❌ (Node: function)

Root cause / context

This is the next layer beyond #5269 (which made native ctor-class exports expose a real .prototype object). The .prototype object exists but its methods aren't accessible on it: EventEmitter is handle-based (EventEmitterHandle / js_event_emitter_new), and instance emit/on dispatch natively keyed on the instance handle — but a plain property GET of emit on the prototype object resolves nothing.

class X extends EventEmitter {} already works (subclass instances dispatch emit), so the "non-direct-EventEmitter object behaves as an emitter" machinery exists for the subclass path; the setPrototypeOf mixin path doesn't hook into it.

What a fix needs

1. EventEmitter.prototype.emit/.on/… resolve to the native methods (so the property GET / proto-chain lookup finds them).
2. Those methods work with an arbitrary this (a plain object whose proto chain includes EventEmitter.prototype), i.e. lazily attach emitter state on first on/emit — mirroring how class … extends EventEmitter instances become emitters. Without (2), exposing the methods just moves the error to "native emit on a non-emitter this".

Impact

pino, and any library using the setPrototypeOf(proto, EventEmitter.prototype) mixin (a common pattern). Distinct from #5268 (that was the Object.create/__proto__ proto-resolves-to-undefined crash, fixed by #5269; pino now loads past it and fails here instead).