lib: undoing accidental changes

Some Changes I just sent wasn't related to the PR in question,
so I'm undoing then (in events.js and the addition of linkedMap.js)
Also, fixed the [SymbolAsyncIterator] function returned by
eventsToAsyncIteratorFactory, that was referencing a no longer
available variable

lib/events.js

@@ -27,7 +27,6 @@ const {
   ArrayPrototypeShift,
   ArrayPrototypeSlice,
   ArrayPrototypeSplice,
-  ArrayFrom,
   Boolean,
   Error,
   ErrorCaptureStackTrace,
@@ -64,7 +63,6 @@ const {
     ERR_UNHANDLED_ERROR
   },
 } = require('internal/errors');
-const getLinkedMap = require('internal/linkedMap');
 
 const {
   validateAbortSignal,
@@ -388,19 +386,30 @@ EventEmitter.prototype.emit = function emit(type, ...args) {
   if (handler === undefined)
     return false;
 
-  const listeners = ArrayFrom(handler);
-  const len = handler.length;
-  for (let i = 0; i < len; ++i) {
-    const result = listeners[i].apply(this, args);
+  if (typeof handler === 'function') {
+    const result = handler.apply(this, args);
 
     // We check if result is undefined first because that
     // is the most common case so we do not pay any perf
-    // penalty.
-    // This code is duplicated because extracting it away
-    // would make it non-inlineable.
+    // penalty
     if (result !== undefined && result !== null) {
       addCatch(this, result, type, args);
     }
+  } else {
+    const len = handler.length;
+    const listeners = arrayClone(handler);
+    for (let i = 0; i < len; ++i) {
+      const result = listeners[i].apply(this, args);
+
+      // We check if result is undefined first because that
+      // is the most common case so we do not pay any perf
+      // penalty.
+      // This code is duplicated because extracting it away
+      // would make it non-inlineable.
+      if (result !== undefined && result !== null) {
+        addCatch(this, result, type, args);
+      }
+    }
   }
 
   return true;
@@ -433,29 +442,36 @@ function _addListener(target, type, listener, prepend) {
 
   if (existing === undefined) {
     // Optimize the case of one listener. Don't need the extra array object.
-    existing = events[type] = getLinkedMap().push(listener);
+    events[type] = listener;
     ++target._eventsCount;
-  } else if (prepend) {
-    existing.unshift(listener);
   } else {
-    existing.push(listener);
-  }
+    if (typeof existing === 'function') {
+      // Adding the second element, need to change to array.
+      existing = events[type] =
+        prepend ? [listener, existing] : [existing, listener];
+      // If we've already got an array, just append.
+    } else if (prepend) {
+      existing.unshift(listener);
+    } else {
+      existing.push(listener);
+    }
 
-  // Check for listener leak
-  m = _getMaxListeners(target);
-  if (m > 0 && existing.length > m && !existing.warned) {
-    existing.warned = true;
-    // No error code for this since it is a Warning
-    // eslint-disable-next-line no-restricted-syntax
-    const w = new Error('Possible EventEmitter memory leak detected. ' +
-                        `${existing.length} ${String(type)} listeners ` +
-                        `added to ${inspect(target, { depth: -1 })}. Use ` +
-                        'emitter.setMaxListeners() to increase limit');
-    w.name = 'MaxListenersExceededWarning';
-    w.emitter = target;
-    w.type = type;
-    w.count = existing.length;
-    process.emitWarning(w);
+    // Check for listener leak
+    m = _getMaxListeners(target);
+    if (m > 0 && existing.length > m && !existing.warned) {
+      existing.warned = true;
+      // No error code for this since it is a Warning
+      // eslint-disable-next-line no-restricted-syntax
+      const w = new Error('Possible EventEmitter memory leak detected. ' +
+                          `${existing.length} ${String(type)} listeners ` +
+                          `added to ${inspect(target, { depth: -1 })}. Use ` +
+                          'emitter.setMaxListeners() to increase limit');
+      w.name = 'MaxListenersExceededWarning';
+      w.emitter = target;
+      w.type = type;
+      w.count = existing.length;
+      process.emitWarning(w);
+    }
   }
 
   return target;
@@ -548,10 +564,39 @@ EventEmitter.prototype.removeListener =
       const list = events[type];
       if (list === undefined)
         return this;
-      if (list?.remove(listener)) {
-        if (list.length === 0) {
+
+      if (list === listener || list.listener === listener) {
+        if (--this._eventsCount === 0)
+          this._events = ObjectCreate(null);
+        else {
           delete events[type];
+          if (events.removeListener)
+            this.emit('removeListener', type, list.listener || listener);
+        }
+      } else if (typeof list !== 'function') {
+        let position = -1;
+
+        for (let i = list.length - 1; i >= 0; i--) {
+          if (list[i] === listener || list[i].listener === listener) {
+            position = i;
+            break;
+          }
+        }
+
+        if (position < 0)
+          return this;
+
+        if (position === 0)
+          list.shift();
+        else {
+          if (spliceOne === undefined)
+            spliceOne = require('internal/util').spliceOne;
+          spliceOne(list, position);
         }
+
+        if (list.length === 1)
+          events[type] = list[0];
+
         if (events.removeListener !== undefined)
           this.emit('removeListener', type, listener);
       }
@@ -675,7 +720,19 @@ EventEmitter.prototype.listenerCount = listenerCount;
  * @returns {number}
  */
 function listenerCount(type) {
-  return this._events?.[type]?.length || 0;
+  const events = this._events;
+
+  if (events !== undefined) {
+    const evlistener = events[type];
+
+    if (typeof evlistener === 'function') {
+      return 1;
+    } else if (evlistener !== undefined) {
+      return evlistener.length;
+    }
+  }
+
+  return 0;
 }
 
 /**

lib/internal/readline/eventsToAsyncIteratorFactory.js

@@ -102,6 +102,6 @@ module.exports = function eventsToAsyncIteratorFactory(readable, {
     get queueSize() {
       return queueSize;
     },
-    [SymbolAsyncIterator]() { return result; },
+    [SymbolAsyncIterator]() { return this; },
   };
 };