Fixes #13343 (#13360)

src/js/node/events.ts

@@ -438,12 +438,20 @@ function getEventListeners(emitter, type) {
   return getEventListenersForEventTarget(emitter, type);
 }
 
-function setMaxListeners(n, ...eventTargets) {
+// https://github.com/nodejs/node/blob/2eff28fb7a93d3f672f80b582f664a7c701569fb/lib/events.js#L315-L339
+function setMaxListeners(n = defaultMaxListeners, ...eventTargets) {
   validateNumber(n, "setMaxListeners", 0);
-  var length;
-  if (eventTargets && (length = eventTargets.length)) {
-    for (let i = 0; i < length; i++) {
-      eventTargets[i].setMaxListeners(n);
+  const length = eventTargets?.length;
+  if (length) {
+    for (let eventTargetOrEmitter of eventTargets) {
+      // TODO: EventTarget setMaxListeners is not implemented yet.
+      // Only EventEmitter has it.
+      if ($isCallable(eventTargetOrEmitter?.setMaxListeners)) {
+        eventTargetOrEmitter.setMaxListeners(n);
+      } else if ($isObject(eventTargetOrEmitter) && eventTargetOrEmitter instanceof EventTarget) {
+        // This is a fake number so that the number can be checked against with getMaxListeners()
+        eventTargetOrEmitter[eventTargetMaxListenersSymbol] = n;
+      }
     }
   } else {
     defaultMaxListeners = n;
@@ -527,9 +535,9 @@ function validateBoolean(value, name) {
 
 let AsyncResource = null;
 
+const eventTargetMaxListenersSymbol = Symbol("EventTarget.maxListeners");
 function getMaxListeners(emitterOrTarget) {
-  // TODO: apparently EventTarget in Node can have a max number of listeners?
-  return emitterOrTarget?._maxListeners ?? defaultMaxListeners;
+  return emitterOrTarget?.[eventTargetMaxListenersSymbol] ?? emitterOrTarget?._maxListeners ?? defaultMaxListeners;
 }
 
 // Copy-pasta from Node.js source code

test/js/node/events/event-emitter.test.ts

@@ -4,7 +4,7 @@ import { createRequire } from "module";
 
 // this is also testing that imports with default and named imports in the same statement work
 // our transpiler transform changes this to a var with import.meta.require
-import EventEmitter, { getEventListeners, captureRejectionSymbol } from "node:events";
+import EventEmitter, { getEventListeners, captureRejectionSymbol, setMaxListeners, getMaxListeners } from "node:events";
 
 describe("node:events", () => {
   test("captureRejectionSymbol", () => {
@@ -853,6 +853,23 @@ test("getMaxListeners", () => {
   expect(emitter.getMaxListeners()).toBe(20);
 });
 
+test("setMaxListeners", () => {
+  const emitter = new EventEmitter();
+  expect(emitter.getMaxListeners()).toBe(10);
+  emitter.setMaxListeners(20);
+  expect(emitter.getMaxListeners()).toBe(20);
+
+  setMaxListeners(30, emitter);
+  expect(emitter.getMaxListeners()).toBe(30);
+
+  const eventTarget = new EventTarget();
+  setMaxListeners(1, eventTarget);
+  expect(getMaxListeners(eventTarget)).toBe(1);
+
+  setMaxListeners(99, eventTarget);
+  expect(getMaxListeners(eventTarget)).toBe(99);
+});
+
 test("getEventListeners", () => {
   const target = new EventTarget();
   expect(getEventListeners(target, "hey").length).toBe(0);